Digestion and Nutrition

THE HUMAN BODY How It Works Digestion and Nutrition THE HUMAN BODY How It Works Cells, Tissues, and Skin The Circulatory System Digestion and Nutrition The Endocrine System Human Development The Immune System The Nervous System The Reproductive System The Respiratory System The Senses The Skeletal and Muscular Systems THE HUMAN BODY How It Works Digestion and Nutrition Robert Sullivan . or sales promotions. some addresses and links may have changed since publication and may no longer be valid. — (The human body: how it works) Includes bibliographical references and index. 2. All links and Web addresses were checked and verified to be correct at the time of publication.chelseahouse. Title. Digestive organs. including photocopying.com Text design by Erika Arroyo. ISBN 978-1-60413-367-7 (hardcover) 1. Because of the dynamic nature of the Web. Nutrition. associations. institutions. Digestion. p. QP145.S86 2008 612. electronic or mechanical. You can find Chelsea House on the World Wide Web at http://www. No part of this book may be reproduced or utilized in any form or by any means. or by any information storage or retrieval systems. recording.DIGESTION AND NUTRITION Copyright © 2009 by Infobase Publishing All rights reserved. Please call our Special Sales Department in New York at (212) 967-8800 or (800) 322-8755. Erik Lindstrom Cover design by Ben Peterson Printed in the United States of America Bang FOF 10 9 8 7 6 5 4 3 2 1 This book is printed on acid-free paper. (Robert James) Digestion and nutrition / Robert Sullivan. 3. without permission in writing from the publisher.3—dc22 2008030741 Chelsea House books are available at special discounts when purchased in bulk quantities for businesses. contact: Chelsea House An imprint of Infobase Publishing 132 West 31st Street New York NY 10001 Library of Congress Cataloging-in-Publication Data Sullivan. Robert J. cm. For information. . I. Houston. M. Cooley. Absorption.Contents Introduction Denton A. and Elimination Chewing and Swallowing The Stomach and Small Intestine The Large Intestine and Elimination Common Health Problems Guides to Healthy Eating 6 1 2 3 4 5 6 7 8 9 10 12 23 32 41 52 67 76 80 98 99 110 111 114 115 120 Appendix: Conversion Chart Glossary Bibliography Further Resources Picture Credits Index About the Author . President and Surgeon-in-Chief of the Texas Heart Institute Clinical Professor of Surgery at the University of Texas Medical School.D. Texas Introduction to Digestion and Nutrition Nutrition and Major Nutrients Minor Nutrients and Metabolism Digestion. we take the body for granted. From a purely physical standpoint. it is a source of strength. pain is a very effective alarm system that lets us know the body needs attention. sulfur. Our cells and tissues are constantly wearing out and being replaced without our even knowing it. We are also made of many minerals. In fact. sodium. If the pain does not go away. we do not normally think about these things. When it is working properly. and reproductive systems. including the musculoskeletal. If we cut ourselves. When something goes wrong. the blood-clotting system works to seal the cut right away. endocrine. We can compare the healthy body to a welldesigned machine whose parts work smoothly together.000 times per day and we breathe more than 10 million times per year. We can also compare it to a symphony orchestra in which each instrument has a different part to play. and organs. In fact. beauty. Related organs are combined into systems. our bodies tell us through pain and other symptoms. the elements of the body are organized into cells. cardiovascular. Although the heart beats about 100. however. potassium. At best. In order of size. much of the time. and iron. Even without medical help. and the immune  . gastrointestinal. our bodies are made mainly of water. we tend to ignore it. tissues. and wonder.Introduction The human body is an incredibly complex and amazing structure. nervous. phosphorous. respiratory. the body has an amazing ability to heal itself. When all of the musicians play together. they produce beautiful music. including calcium. chlorine. we may need to see a doctor. magnesium. Today. researchers are doing a lot of work at the cellular level. polio. Scientists recently finished mapping the human genome. If the entire heart is diseased. they cannot always be cured with surgery. the introduction of modern vaccines allowed us to prevent childhood illnesses. which is a set of coded . the use of mechanical hearts will probably be common in patients who would otherwise die of heart disease. and many other bacterial diseases.Introduction  defense system sends out special blood cells that are programmed to heal the area.” After penicillin and other antibiotics became available in the 1930s and 1940s. During the past 50 years. and other contagions that used to kill or cripple thousands. Now that these diseases can be avoided. Even a simple scratch could become infected and lead to death from “blood poisoning. Until the mid-twentieth century. and connections. we can replace it altogether. Because chronic diseases tend to involve many organ systems or even the whole body. In the future. either with a donor heart or with a mechanical device. In my own field of cardiovascular surgery. people are living long enough to have long-term (chronic) conditions such as cancer. we are able to open the heart and repair its valves. arteries. these repairs can be done through a tiny “keyhole” incision that speeds up patient recovery and leaves hardly any scar. tuberculosis. plagues such as the “Spanish flu” epidemic of 1918–1919. which killed 20 to 40 million people worldwide. and arthritis. These days. infections and contagious diseases related to viruses and bacteria were the most common causes of death. doctors were able to treat blood poisoning. chambers. trying to find the underlying causes of chronic illnesses. smallpox. are unknown except in history books. Also. flu. heart failure. diabetes. In many cases. doctors have gained the ability to repair or replace almost every part of the body. pneumonia. water. or other serious disorders. sex. The average person knows more about the human body than ever before. and refuse to smoke. we tend to be stressed. we can do something about most of these risk factors. In western Europe and the United States. abusing alcohol. in making medical decisions and in taking care of their own health. overweight. the human genome will help researchers prevent and treat disease at its source. heart disease. and environment. I encourage you to learn as much as you can about your body and to treat your body well. or using drugs. get enough sleep. Fortunately. or use addictive drugs. and out of shape. is an excellent introduction . We can also help clean up our environment. but is not always good for our bodies. the most important things we can do for our bodies are to eat right. overuse alcohol. By showing how the body is made. including our age. Our modern lifestyle offers many advantages. dIgestIon and nutrItIon “instructions” programmed into our cells. are beyond our control. Other important risk factors include our lifestyle. The body’s long-term health depends on many factors. along with their doctors. The Human Body: How It Works. These days. while you are young. At any age. These simple steps will lower our chances of getting cancer. Each cell contains 3 billion “letters” of this code. Some risk factors. people are more aware of health-related matters. Patients want to understand their medical conditions and treatment options. These things may not seem too important to you now. thanks to the Internet and other forms of media coverage. and food often contain hazardous chemicals and industrial waste products. They want to play a more active role. This book series. within the cells themselves. Many of us have unhealthy habits such as smoking cigarettes. behavior. Our air. but the habits and behaviors that you practice today will affect your physical well-being for the rest of your life. and family history of certain diseases. called risk factors. exercise regularly. Houston. Denton A.Introduction  to human biology and anatomy. President and Surgeon-in-Chief of the Texas Heart Institute Clinical Professor of Surgery at the University of Texas Medical School. Texas .D. I hope that it will awaken within you a lifelong interest in these subjects. Cooley. M. she has been thinking about the chocolate shake all morning. first physically into smaller and smaller pieces. besides. fries. and a chocolate shake. She knows the burger and fries have lots of fat and salt that she does not need. and taste and breaks it down. Amy stops for lunch at a fast-food restaurant. and she knows that the meal will be served fast and that the food will be safe. smell. These nutrients are relatively simple chemicals that can pass through the cells in the walls of the digestive tract and into the blood. which transports them to all the cells of the body. She is in a hurry. This process takes the food we can see. her digestive system processes the hamburger. After Amy eats her lunch. She has a form of lactose intolerance that sometimes results in abdominal cramping and diarrhea after ingesting milk products. She orders a burger.1 Introduction to Digestion and Nutrition On the way home from her morning classes. and at least she knows what she gets here. But she is in a hurry. and chocolate milkshake into nutrients her body can use. The food may not be the tastiest in the world or very good for her. and then chemically into nutrients that can be used by the cells. Amy has eaten in this kind of place hundreds of times before. fries. She also knows the shake is risky for her. but it will get her through until dinner. 10 . Introduction to digestion and nutrition Digestion is the physical and chemical breakdown of 11 food into forms that can be used by the body’s cells. The process begins in the mouth when a bite of food is chewed, thereby breaking it down into smaller pieces and mixing it with saliva. The food mass is then swallowed. The food has been reduced to a smaller size, but it is still not small enough. Digestion continues in the stomach and intestines until the food particles are an appropriate size and the nutrients can travel to the body’s cells. The process by which nutrients pass through the walls of the digestive tract and into the blood is called absorption. The blood transports the nutrients to the cells of the body, where they are absorbed to provide energy and needed structural materials. As you read through the chapters, you will follow Amy’s lunch on its journey through her body. You will read about what is really in her food, how it is digested, or broken down, and how it is absorbed into the cells. The hamburger and fries she eats contain a lot of fat and salt, and the milkshake will most likely make her feel sick. You will also learn how this is related to her lactose intolerance. You will read about why we need nutrients. Why do we need a variety of carbohydrates, proteins, lipids, vitamins, and minerals? If we cannot absorb food until it is broken down into much smaller pieces, how does it get into the body? There is also a discussion of accessory organs that contribute to digestion, such as the liver and pancreas. Finally, this book will discuss some nutritional controversies and health problems related to the digestive tract and nutrition. Digestive anatomy and physiology are integrated as much as possible throughout the chapters. As you read about the anatomy of a specific portion of the digestive tract, the physiology, or the way this portion works, is discussed. 2 Nutrition and Major Nutrients Why Do hUMANS hAve To eAT? Humans and other animals need to eat because they need resources that their bodies cannot provide. Food provides the material for the structural needs of the body, such as replacing worn-out cells and tissues, building more muscle tissue, and growth. In order to fulfill these needs, the body also needs the energy that food provides. This energy is used to make and break chemical bonds in complex biochemical compounds, to hold these compounds together, and to change them. The digestive system and its accessory organs have evolved to supply individuals with the energy they need to work with these chemical bonds. There are three types of chemical bonds. An ionic bond forms between charged atoms where positive and negative charges attract each other. These bonds are fairly strong, but not so strong that energy is needed to alter them. A hydrogen bond is a type of weak chemical bond. It bonds substances together during chemical reactions or fine-tunes the structure of complex compounds so that they can function properly. Hydrogen bonds also exist between water molecules and anything mixed 12 nutrition and Major nutrients 13 in water. Hydrogen bonds allow the water molecules to support the compounds that are dissolved in the solution, but are weak enough to allow the compounds to diffuse through the water. Hydrogen bonds are so weak that the chemicals held with them can separate just by drifting off into the surrounding water. The third type of chemical bond, a covalent bond, requires energy to make or break it. Covalent bonds are formed when atoms share electrons. The electrons from two or more atoms are found in the space around the nuclei of the atoms, forming a tight bond, almost like a wall. Energy released by the breaking of chemical bonds must be put into a form that cells can use. The chemical energy used by cells is stored in the bonds of adenosine triphosphate (ATP), an RNA nucleotide. The three phosphates in ATP are attached to the adenosine in series so that the molecule looks like this: A-P-P-P (Figure 2.1). The phosphates are negatively charged and repel each other. Attaching the second and third phosphate requires energy to force the phosphates onto the molecule. The energy stored in ATP is the energy in the bonds that hold the repelling phosphates together. When the energy is needed, the third phosphate is removed, and the energy that was holding the phosphate onto the ATP molecule is used to make or break a covalent bond. The loss of the phosphate from the ATP produces adenosine diphosphate (ADP). ADP can become ATP by extracting energy from a nutrient and using it to attach another phosphate. These energy transport molecules function like rechargeable batteries, with the difference being that the energy is mostly discharged each time the ATP is used. TypeS of NUTrieNTS There are major and minor nutrients. Major nutrients—carbohydrates , proteins , and lipids —serve as energy sources or as building blocks for larger biochemical compounds. Minor nutrients, which include all vitamins and minerals , assist the chemical reactions that occur with major nutrients. some energy sources or building blocks will be missing. Cells obtain the energy they need to carry on their life functions from the breakdown of atP.14 dIgestIon and nutrItIon figure 2. the energy released can be used by the cell for anything from replication and division to making proteins and extracting nutrients from food. A balanced diet includes all of the necessary major and minor nutrients.1 atP is an energy–storage compound that contains three phosphate groups. . If the diet is not balanced. When the bond between the last two phosphate groups is broken. and the body will not function properly. and polysaccharides . which is made of glucose and fructose. are simple sugars. Each one has glucose as at least one of its sugar units. or complex sugars. and galactose. or complex carbohydrates. a group of molecules that include sugars and starches . Monosaccharides Monosaccharides. The body’s sugar biochemistry is based on the breakdown of glucose. Because disaccharides are too large to pass through cell membranes. is found in anything “malted” and is also the sugar primarily used to make beer. Most of the sugars used in the body are six-carbon sugars. lactose. such as glucose. the ratio of carbon to hydrogen to oxygen is 1:2:1 such that there is one carbon to two hydrogens to one oxygen. and maltose. Lactose. provide energy for the body when the molecules are broken down. and oxygen. All carbohydrates contain carbon. hydrogen. Polysaccharides Polysaccharides. so their formula is written as C6H12O6. Maltose. There are three types of disaccharides: sucrose. Fructose and galactose feed into the pathway of these chemical reactions. Sucrose. Usually. There are two . is common table sugar.nutrition and Major nutrients 15 Carbohydrates Carbohydrates. disaccharides . they must be broken down into monosaccharides before they can be used by the body. made of glucose and galactose. fructose. Disaccharides Two monosaccharides bonded together form a disaccharide. is the sugar found in dairy products. are composed of many monosaccharides linked in a chain. made of two glucose molecules. They are categorized by size: monosaccharides . Polysaccharides must be digested to their individual glucose units for the body to be able to use the energy. Glycogen is similar to amylopectin. although the primary source is beef. As mentioned earlier. which may lead to increased fat production. The liver can convert amino acids into glucose. Both plants and animals use polysaccharides as a form of short-term energy storage. There are two types of starch.1 dIgestIon and nutrItIon types of polysaccharides of importance to the body: starches and glycogen.and disaccharides are found in fruits. they are converted to glycogen or fat and stored. depending on their source and the types of chemical bonds holding them together. Amylose is easily digestible and has a simple structure resembling a bunch of strings made up of glucose molecules linked together in a straight line. Starches are storage carbohydrates found in plants. a process called gluconeogenesis. These are made up of glucose subunits and have slightly different forms. the liver breaks down glycogen to release glucose. . and is more difficult for the body to digest. honey. including a large number of crosslinkages between the strings. Starches are found in grains. and root vegetables. Glycogen is the storage carbohydrate form found in animals. amino acids are converted to glucose instead of being used in protein synthesis. Simpler sugars provide a spike in absorbed sugars. and milk. This longer time provides a steady supply of monosaccharides for absorption and metabolism. sugarcane. If carbohydrates are not immediately needed. When glucose is broken down. If not enough glucose is available. legumes. Amylopectin has a more complex structure. some of the energy released from the chemical bonds goes into the synthesis of ATP from ADP molecules. sugar beets. Mono. but less complex. molasses. Glycogen is present in all animals. carbohydrates are used for energy. Polysaccarides in food take longer to digest and absorb than simple sugars or dissacharides. depending on the complexity of the structure: amylose and amylopectin. If adequate sugar is not available in the diet. this means that the item is made mostly of sugar. they form part of a balanced diet that fills our nutritional needs. and minerals. keratin. which are strandlike in appearance. They include collagen. vitamins. and the contractile proteins of muscles. lipids. Proteins are made of long chains of 20 different kinds of amino acids. it is considered roughage or fiber. In general. including muscle. depending on the sequence of the amino acids. and not much of anything else. so it is not digestible. It is a major component of wood. The chains of amino acids bend and twist to a three-dimensional form. Fibrous proteins. It cannot be broken down into smaller units by the human digestive system. Collagen provides strength to the tendons and ligaments that hold bones and muscle together. When we ingest cellulose. and they are basic components of hormones and enzymes. Keratin is found in the outermost layer of skin.” proTeiNS Proteins have many functions in the body. Although we get no nutritional value from cellulose. . they form many different structural parts. are called structural proteins. The function of a protein depends on its structure. where it “seals” YOUR HEALTH: EMPTY CALORIES sometimes foods are described as having empty calories. When carbohydrates are ingested along with proteins.nutrition and Major nutrients 1 Cellulose is a type of polysaccharide found in plants. The structure of proteins ranges from small and simple to large and very complex. They can be used for energy. Fiber also helps to regulate the digestive tract and keep people “regular. it binds cholesterol in the intestine and helps us eliminate this chemical. probably sucrose. the structure and appearance of proteins can be classified as fibrous or globular. 1 dIgestIon and nutrItIon the skin surface. such as premature aging. such as human growth hormone. The most complete sources of dietary proteins are found in animal tissues because they contain all the essential amino acids. which are compact. These eight amino acids are tryptophan. and isoleucine. Plants can also provide amino acids. Contractile proteins of muscles allow muscle tissue to contract. the production of proteins is equal to the breakdown of proteins. Enzymes are globular proteins that increase the rate of chemical reactions in the body. or shorten. the production of protein exceeds protein breakdown. preventing evaporation of water from underlying tissues and keeping invading microorganisms out. If they are not supplied. Globular proteins. methionine. they must be supplied in the diet. which helps regulate growth in the body. and the . proTeiNS AND DieT Of the twenty different amino acids. Nitrogen balance is an evaluation of the amount of protein in the body. but you may have to eat more than one kind of plant food at one meal to supply all the essential amino acids at the same time. problems in fighting infections. Protein deficiencies in adults cause a number of problems. there are eight. In a healthy person. valine. and it is used to determine an individual’s nutritional status. and bleeding in joints and the digestive tract. It is also a major component of hair and nails. called essential amino acids. Some are found in hormones. Protein deficiency during childhood can result in developmental problems that restrict both mental and physical development. that the human body cannot synthesize. proteins cannot be made. threonine. spherical proteins. and the nitrogen balance is said to be neutral. In a person who is growing or repairing tissue damage and has adequate amino acid resources for protein production. lysine. leucine. which results in a protein deficiency. have a wide variety of functions. histadine. Because humans cannot make them. The terms lipids and fats can usually be used interchangably. while fats are more solid at room temperatures. which is not good. The principal dietary lipids in the body are cholesterol (a steroid) and triglycerides. phospholipids. make up a major portion of adipose tissue. Saturated triglycerides contribute more to the buildup of plaque in arteries and are considered less healthy than unsaturated fats. These forms of triglycerides behave slightly differently in the body. The fatty acid portion of the triglyceride is the “fat” in the molecule and gives it the lipid characteristics. except those derived from coconuts or the palm tree. and thus they are difficult to carry in the blood. and unsaturated triglycerides are found in nearly all plants. is said to be a saturated fat. or the triglyceride. Phospholipids are mostly tied up in cell membranes and do not play a significant role in energy metabolism. If any of the hydrogen atoms are missing. the fatty acid is unsaturated. the person is said to be in negative nitrogen balance. This tissue provides the body with insulation to keep warm and cushions joints and organs for protection. Lipids are categorized as triglycerides. Fatty acids are chains of 12 to 30 carbon atoms. which are made in the liver to store excess energy from carbohydrates. Triglycerides. If all the possible hydrogen atoms are attached to the chain. If proteins are being broken down faster than the body can replace them. Attached to the carbon atoms are hydrogen atoms. fATS AND LipiDS Lipids are insoluble in water. Saturated triglycerides are found in all animal tissues. Negative nitrogen balance means that the person needs supplemental proteins and amino acids to achieve a neutral or positive nitrogen balance. and steroids. the fatty acid. Just as there are . Lipids are frequently liquid.nutrition and Major nutrients 1 person is said to be in positive nitrogen balance. Triglycerides are composed of three-carbon glycerol molecules with a fatty acid molecule attached to each of the three carbons. and linoleic acid. which is water-based. and triglycerides and sent into the blood to deliver these fats to the body’s tissues. growth retardation. If part of the plaque breaks off from the vessel wall. When this blockage occurs in the blood vessels of the heart. just not in excess. especially corn and safflower oils. and cardiac. thus. Linoleic acid is found in vegetable oils. a depressed immune system. these floating lipids attach to fatty deposits called plaque on the walls of blood vessels (Figure 2. Linoleic acid is also called omega-6 fatty acid and α-linolenic acid is called omega-3 fatty acid. anemia. there are two types of essential fatty acids that must be supplied by the diet: linoleic acid and α-linolenic acid (α is the Greek letter alpha). such as cholesterol and triglycerides.2). all dietary fats are needed by the body. different proteins give different characteristics to these lipid-protein mixtures. where it may get stuck and completely block the smaller vessel. especially if there is an increase . a heart attack results. oleic acid. If the fats separate from their protein carriers. liver. for the body to carry lipids. neither one of them is good or bad. Essential fatty acid deficiencies contribute to dermatitis. infertility. If the plaque becomes large enough. DID YOU KNOW? Fats are not soluble in water. and α-linolenic oil is found in rapeseed oil. If this blockage occurs in the brain. the lipids and proteins tend to separate. cholesterol. it can close off part of the blood vessel.) In the blood. in the blood. the proteins act as carriers for the fats.20 dIgestIon and nutrItIon essential amino acids that must be supplied by the diet. it can travel to capillaries. the lipids are mixed with proteins that can dissolve in water. stearic acid. a stroke results. they can no longer travel in the blood or mix well in cells. which are called hDL (high-density lipoprotein) and LDL (low-density lipoprotein). and respiratory problems. About 90% of the body’s dietary fat intake consists of the fatty acids palmitic acid. (this is analogous to the separation of water and oil in salad dressing. LdL is assembled in the liver from proteins. It is estimated that Americans consume about a bit less than 6% of their fats as trans fats. as in hypertension. this plaque can grow large enough to block the flow of blood through the vessel. in blood pressure. extra fat in the body can accumulate in blood vessels and form plaque. These are unsaturated fatty acids that have some of the harmful properties of saturated fats. Plaque that occurs in the major vessels of the heart can cause a heart attack.2 Plaque (yellow) blocking the aorta. LdL has earned the name “bad cholesterol. the arrangement of the hydrogens in these molecules produces damage to the heart and blood vessels. thus. Although trans fats contain unsaturated fatty acids. The figure 2. a digestive fluid. The advantage of using trans fats in food products for commercial use is that they have a longer shelf life and allow prepared foods to stay fresher longer. Because HdL removes cholesterol from tissues and does not significantly contribute to the buildup of plaque. this is slightly less than 3% of our caloric intake. they are removed from the blood by the liver and the cholesterol is made into bile.” .” HdL protein is made in the liver and released into the bloodstream without any lipids. it has earned the name “good cholesterol.nutrition and Major nutrients 21 TrANS fATS Some triglycerides contain what are called trans fats. When the HdL proteins are full of cholesterol. Its job is to scavenge cholesterol from the body’s tissues and blood vessels. They also found in prepared meats and hard margarine. from cell repair to muscle contraction. such as cakes. a steroid hormone from the adrenal cortex. but this compound cannot be absorbed by humans and does not contribute to dietary fats. are both steroids. Testosterone and estrogen. Cholesterol forms the chemical framework of steroid hormones. and breads. Cholesterol is also found in cell membranes. both major and minor. Cholesterol. is both made in the liver and ingested in food from animal sources. Plants have a counterpart to cholesterol called phytosterol. . pies. Aldosterone. These fatty acids contribute as much to the clogging of arteries as saturated fats. but they are not. which are reproductive hormones. Steroids are another type of lipid that have hydrocarbon rings.22 dIgestIon and nutrItIon hazard to consumers is that they think they are substituting unsaturated fats for saturated ones in their diets. Trans fats are most frequently found in prepared foods. where it makes them pliable. Vitamins and minerals are types of minor nutrients and will be discussed in Chapter 3. and lipids. proteins. ConneCtions The body takes food and breaks it down into the nutrients it can use. Nutrients serve as building blocks for larger chemicals and the energy that fuels all of the body’s processes. assists in the renal conservation of sodium. Its presence in the membranes of red blood cells allows the cells to squeeze through small capillaries. cookies. one of the most important steroids. The major nutrients include carbohydrates. Vitamins do not supply energy or serve as building blocks for other compounds. modify. Fatsoluble vitamins are stored in the body and may reach toxic levels if a person ingests too much of them.3 Minor Nutrients and Metabolism Although sugars. This chapter examines these nutrients and also includes a brief discussion of the way we actually extract energy from nutrients through biochemical pathways. they work with the chemicals that make.1 for details on these vitamins.) Vitamin D is made in the skin when it is exposed to ultraviolet light from the sun. Nutri23 . D. Vitamins are classified as either fat or water soluble. viTAMiNS Vitamins and minerals are classified as minor nutrients. proteins. vitamins and minerals also play a vital role in our diet. These compounds are vital to the body. and K. Instead. (See Table 3. E. The four fat-soluble vitamins are A. and fats receive a lot of attention in discussions of nutrition. and lipids. and metabolize the major nutrients. proteins. These vitamins are absorbed the same way as other fats (see Chapter 6). but are needed in much smaller amounts than carbohydrates. A common blood thinner taken after a heart attack or stroke inactivates vitamin K and decreases the blood-clotting factors from the liver. including vitamin C and several B vitamins. Vitamin K is found in many leafy vegetables. Vitamin K is involved in the process of blood clotting. inability of blood to clot Scurvy K Production of blood clotting factors Antioxidant C (Ascorbic acid) B Complex Energy carriers in metabolism Participates in DnA synthesis Participates in DNA synthesis Metabolism problems Anemia Anemia B12 Folic acid . The decrease in clotting factors results in a lower tendency to clot and helps prevent a second heart attack or stroke.1 ImporTanT VITamIns viTAMiN A (Retinol) D E iMporTANCe Used for production of chemicals in vision Calcium absorption Antioxidant probLeM exCeSS Neurological problems Neurological problems Neurological problems Neurological problems None—excess secreted in urine None—excess secreted in urine None None probLeM DefiCiT Night blindness “Soft” bones Damage from chemical free radicals Bleeding. and it is also produced by the bacteria that inhabit the intestines (see Chapter 7). Except for storage of vitamin B12 in the liver.24 dIgestIon and nutrItIon tional supplementation of vitamin D is usually necessary during childhood to ensure proper bone growth. none of the water-soluble vitamins are stored Table 3. There are many water-soluble vitamins. in very low concentrations. Metabolism is the . Excess amounts of these vitamins are excreted in the urine. Vitamin B12 is only found in meat. and molybdenum. producing a goiter. Iodine deficiencies result in marked swelling of the thyroid gland and neck. is found in citrus fruits. Thyroid hormone controls the body’s metabolic rate. also called ascorbic acid. and phosphate provide strength to bones and teeth. phosphate. while folic acid is present in leafy vegetables. but no extra folic acid. iodine. People with a deficiency of this hormone have a lower-thannormal metabolic rate. Care should be taken if supplements are used. copper. sulfur. sodium. The body also needs trace metals . chloride. potassium. including calcium. Iodine is a vital part of the hormone made by the thyroid gland. MeTAboLiSM Once nutrients have entered the body cells. such as China. Countries that do not add iodine to their salt. have a high incidence of goiter.Minor nutrients and Metabolism 25 in the body. including zinc. Vitamin C. Calcium. Iron is important in hemoglobin and other oxygen-carrying compounds. they take part in a wide range of biochemical reactions. magnesium. affecting growth and development in childhood and overall body metabolism in adults. MiNerALS The body needs several minerals. During pregnancy. Other vitamins can be found in a variety of fruits and vegetables. as metals such as selenium and chromium are toxic in excess. selenium. Humans usually have about one year’s supply of vitamin B12 stored in the liver. Individuals in the United States usually receive adequate iodine from iodized salt. fluorine. manganese. women are especially prone to folic acid deficiency and need to take supplemental vitamins to help maintain the development of the fetus. magnesium. and iron. . Anabolic reactions usually require the addition of energy to proceed. The rest of the ATP is made by harnessing the energy of the electrons of hydrogen atoms. Phosphorylation is the process of adding a phosphate group (PO4-) to an atom or group of atoms. This energy can be used to add a third phosphate onto ADP to form ATP. a process called substrate phosphorylation. The energy released from one reaction can run another reaction.1). the bonding of amino acids to make proteins. Metabolic reactions either make molecules or structures or break them down. This process accounts for relatively little of the ATP produced. there is energy left over. sum of the chemical reactions that occur in cells. for example.2 dIgestIon and nutrItIon figure 3. When some chemical reactions occur.1 anabolism and catabolism are both metabolic processes. Energy is extracted from compounds in two ways. Catabolism refers to reactions in which large or complex molecules are broken down into smaller ones (Figure 3. Catabolic reactions tend to release energy from the compounds. anabolism is the synthesis of larger molecules from smaller ones. A substrate is a compound being acted upon by an enzyme. while catabolism is the breakdown of larger molecules into smaller ones. Anabolism refers to reactions in which larger molecules are made from smaller ones. If the person eats less than this. 2. when it receives an electron. Oxygen is used in this process.2 on page 2 shows the number of calories burned through different activities. YOUR HEALTH: CALCULATING BMR to estimate the number of calories the body needs each day.2). but only at the end. If a person changes their level of activity. the result is the number of calories a person should burn in a day to maintain body weight. The addition of two electrons to oxygen attracts two hydrogen ions (protons) from the surrounding medium. storing twice the energy of carbohydrates. table 3.. or is recovering from an illness. the person will gain weight. the number of calories should be adjusted appropriately. The overall process by which energy for metabolism is extracted from nutrients is called cellular respiration. If the person eats more calories than this. Because triglycerides hold a large number of hydrogen atoms. Males should then proceed to the next step. the person will lose weight. Females should first multiply the kilogram figure by 0. fatty acids are much more efficient as energy storage molecules. 1. is actively growing. then proceed to step 2. while those of anaerobic cellular respiration do not require oxygen. . This second method of producing ATP is called oxidative phosphorylation. The reactions of aerobic cellular respiration require oxygen.Minor nutrients and Metabolism 2 These atoms are split. the basic metabolic rate (BMr) must be calculated. and the result is water (H2O). Calculate body weight in kilograms (pounds divided by 2. Multiply this number by 24. and the electrons are passed through a series of reactions resulting in a large amount of ATP. 2 glucose is broken down to carbon dioxide and water by some reactions of glycolysis. Pyruvic acid loses a carbon and becomes acetyl Coa. the result is 34 molecules of atP. First. a -carbon sugar. glucose.2 dIgestIon and nutrItIon figure 3. is broken into two 3-carbon molecules of pyruvic acid. which can be used as a source of energy for the life processes of cells. and the electron transport chain. which produces atP. . electrons from the Krebs cycle enter the electron transport chain. the Krebs cycle. the acetyl Coa enters the Krebs cycle. 5 mph Tennis (singles) of CalorIes burned 240 410 660 1. the Krebs cycle runs twice Table 3. Pyruvic acid loses a carbon dioxide and forms an acetyl group that combines with a form of vitamin B6. the Krebs cycle.2). 10 mph Jumping rope Swimming. Glucose enters glycolysis as a 6-carbon sugar and comes out as two 3-carbon molecules of pyruvic acid. the Krebs cycle.2 approxImaTe number by aCTIVITy ACTiviTy Bicycling. 6 mph Bicycling. resulting in a compound called acetyl CoA.280 750 275 500 240 440 400 per Hour 100 Lb perSoN 160 270 440 850 500 185 325 160 295 265 150 Lb perSoN 200 Lb perSoN 312 534 962 1. Cellular respiration most commonly involves the breakdown of glucose for ATP production using three connected chemical pathways: glycolysis. are aerobic processes in that they cannot continue in the absence of oxygen.5 mph Jogging. This compound enters the second phase of glucose oxidation.664 1. Glycolysis is sometimes an anaerobic process—the reactions can continue in the absence of oxygen. This process also results in the production of two ATP molecules. Because two pyruvic acids produce two acetyl groups. 50 yds/min Walking.000 358 650 312 572 535 . 12 mph Jogging. 25 yds/min Swimming. Other times glycolysis. 4. 5. and the electron transport chain (Figure 3. 2 mph Walking.Minor nutrients and Metabolism 2 All multicelled organisms must carry on aerobic respiration because they cannot survive on the small amount of energy produced by anaerobic processes. as well as the Krebs cycle and the electron transport chain. proteins. and the resulting series of chemical reactions results in the removal of electrons from hydrogen atoms to send to the third phase. Several intermediate chemicals produced during the Krebs cycle can be removed for amino acid synthesis. The waste product of the Krebs cycle is carbon dioxide. The final chemical in the series receives a new acetyl group and the cycle begins again. It is possible to make a total of 38 ATP molecules through the three pathways. Metabolic pathways for carbohydrates. These amino acids can also be fed into the Krebs cycle through these intermediate chemicals. the electron transport chain. During this process. and the production of a single ATP molecule through substrate phosphorylation. the body can use nutrients to make needed compounds. ConneCtions Humans need to eat to gain energy for chemical reactions involving a type of chemical bond called a covalent bond. the maximum number of ATP molecules is seldom produced. is a series of chemical reactions that pass electrons from one chemical to the next. The acetyl group is added to an existing compound in the Krebs cycle. Thus. the electron transport chain. 34 ATP molecules can be produced for each glucose molecule that started the process. The pyruvic acid can also be used to form the amino acid alanine. where all of the ATP is needed for muscle contraction. Because many of the intermediate compounds are used for other purposes. growth. and lipids intersect. which can be transformed into other amino acids. The last pathway.30 dIgestIon and nutrItIon for each glycose molecule broken down. This bond keeps complex biological chemicals together and requires energy that is crucial for repair. or development. or to convert the nutrients to compounds that can . except in skeletal muscle. Carbohydrates exist as monosaccharides. Biologically important polysaccharides come either from plants as starch or from animals as glycogen.Minor nutrients and Metabolism 31 be burned for energy. Deficiencies of vitamins or minerals compromise cell metabolism. proteins. Monosaccharides include glucose. and maltose. Proteins are made from a mixture of 20 amino acids and fulfill a variety of functions in the body. Cholesterol and triglycerides are important dietary lipids. and galactose. Both vitamins and minerals are important in metabolizing the major nutrients of carbohydrates. and lipids. depending on the number of sugar units. Triglycerides are an important form of long-term energy storage and are made from excess carbohydrates. . lactose. disaccharides. fructose. Disaccharides include sucrose. and polysaccharides. Other sugars. and Elimination Let’s get back to Amy and her lunch. sugars. and fats) can be absorbed by the cells in the walls of the digestive tract. proteins.1). Glucose is the simple sugar used most in metabolism.4 Digestion. and anything that enters it must pass through the cells that make up the walls of the tube in order to enter the bloodstream and be transported to the body’s tissues. it is processed and broken down gradually so the nutrients (e. the fries. and are made up of two monosaccharides 32 . how do the nutrients in these foods get to the tissues in her body that need them? This may sound strange. and the shake contain carbohydrates. and chocolate shake. and beer.. or simple sugars. fries. such as those in table sugar. As food passes through the digestive tube. Absorption. Carbohydrates must be broken down to monosaccharides. The question is: When Amy eats her hamburger. The digestive tract is a long tube (about 30 feet when relaxed) with openings at both ends (Figure 4. milk. This tube is contained within the body. but foods that are inside the digestive tract are not yet actually in the body. The hamburger bun. The starch molecules in the bread and potatoes are made up of hundreds of monosaccharides.g. which was discussed in Chapter 1. are disaccharides. As a result of this . small and large intestines. the digestive system includes the mouth. so any disaccharides not broken down to monosaccharides are used by bacteria living in the intestines. bonded together. Anything larger than a monosaccharide cannot be absorbed through the walls of the digestive tube.1 the digestive system is a tube within the body. stomach. absorption. and elimination 33 figure 4. with an opening at the mouth (for intake) and an opening at the anus (for excretion).digestion. esophagus. and rectum. the saturated fatty acids will be transported to the tissue of the body and stored there. (Triglycerides cannot pass through any cell membrane intact. the walls of the organs are made up of four tissue layers: the mucosa. also called lipids.” the body will build up a supply of triglycerides that contains whichever type of dietary fatty acids have been ingested. muscularis. The fatty acid chains can be either saturated or unsaturated. while triglycerides are broken apart every time they enter or leave a cell. may or may not be broken down to get them into the cells lining the digestive tube. which is discussed in Chapter 8. This layer is composed of three parts: the epithelium. (Different types of fats were described in Chapter 2. for example.) Cholesterol is absorbed whole. the lamina propria. or adventitia (Figure 4. These are symptoms that may occur when a person is lactose intolerant. These . Proteins are composed of hundreds of amino acids and must be broken down into individual amino acids in order to be absorbed into the cells lining the digestive tube. The innermost part of the mucosa is the epithelium.) Triglycerides are composed of a single glycerol and three fatty acid chains. submucosa. The innermost layer of the digestive tube is the mucosa. STrUCTUre of The DigeSTive TUbe Throughout the digestive tube.2). The body will use these amino acid building blocks to make body proteins. but cholesterol can. and the muscularis mucosa. as does the oil in which the fries are prepared. Because the fatty acid chains are absorbed through the digestive tube “as is. Most of the epithelial layer is made up of a single layer of cells called columnar epithelial cells. and serosa. Fats. If a person eats food that is high in saturated fatty acids. The beef of the hamburger also contains fats.34 dIgestIon and nutrItIon bacterial metabolism. some people experience abdominal cramping and diarrhea. The meat in the burger is a good source of protein. 2 the walls of the digestive tube are made up of four layers: the mucosa. the muscularis (external muscle layer).digestion. absorption. the submucosa. cells are lined up like columns with one end exposed to the material in the digestive tube and the other end forming the connection between the epithelial layer and the tissue beneath . and the serosa. and elimination 35 figure 4. The submucosa also has some nerves to assist in regulating the digestive process. which are flat and resemble a pancake with a nucleus in the center. which helps protect the tissue underneath them. This protective layer of cells is found in the upper part of the digestive tube. mucussecreting cells called goblet cells because of their unique shape (narrow bottom and wide top) are found throughout the tube. Strong chemicals that are ingested may also be harmful until they are neutralized in the stomach. Everything absorbed into the body must pass through these cells.3 dIgestIon and nutrItIon the lining. . At the beginning of the digestive tube. to protect the tissue from abrasion and prevent further damage to the body. the epithelium is made up of squamous epithelial cells. Beneath the epithelium is the lamina propria. This layer. These adaptations to the submucosa will be discussed in the following chapters. lymph nodules to screen for foreign material that may cause antibodies to be made. the tissue within the wall of the tube would be exposed and subject to further damage and infections from ingested material. The muscularis mucosa has a thin layer of smooth muscle around the lamina propria. depending on the part of the tube. and sometimes glands. similar to the lamina propria but thicker. has connective tissue and blood vessels. In addition to the columnar cells. The second major layer of the digestive tube wall is the submucosa. If a single layer of cells lined this part of the digestive tract and these cells were to die. can be stacked up. This layer helps move food through the digestive tube. a layer of connective tissue that supports the absorptive cells. which are specialized for protection. These cells. when the intestinal contents are dehydrated into feces. as well as on the body surface. The mucus becomes especially important farther along in the tube. This layer contains loose connective tissue with blood and lymphatic capillaries to carry material away from the columnar cells and to the body’s tissues. The muscularis has nerves between the two layers of smooth muscle that assist in regulating peristalsis. Contraction of the outer layer pushes digestive contents through the tube. the covering is called the serosa.3). is sent to the pharynx and then into the esophagus. The only difference is the name given to the covering. The serosa/ adventitia of both cattle and pigs is used commercially as the outer covering or casing on sausages. SUMMAry of The DigeSTive proCeSS The process of taking food into the mouth is called ingestion. absorption. The resulting food mass. The inner layer of muscle is arranged in a circular pattern around the tube. meaning the connective tissue covering of the visceral organs in the abdominal cavity. Contraction of the inner layer nudges the material along with constrictions of the rings of muscle. This layer is made of dense. the outer covering is called the adventitia. The parallel arrangement causes waves of constriction that press on the tube. This layer is similar to the muscularis mucosa. On the esophagus. pushing the material. the ingested food is broken down into smaller pieces and mixed with saliva. In the mouth. In addition to the physical breakdown of food into smaller pieces. and elimination 3 The third layer of the digestive tube wall is the muscularis. The outer layer of muscle cells runs parallel to the tube. some chemical digestion begins in the mouth. especially for . but is much thicker and has two layers of smooth muscle. fibrous connective tissue throughout the tube. Contraction of these muscle layers propels the contents through the digestive tube via a process called peristalsis (Figure 4. called a bolus . and certain types of hot dogs. kielbasa. This covering is also called the visceral peritoneum. based on the location of that part of the tube. At the end of the digestive tube. The last and outermost major layer of the digestive tube is called the serosa.digestion. or adventitia. most enter the bloodstream and go either to the body’s tissues or to the liver. The figure 4. The pancreas contributes enzymes that break down what is left of starch. A specific description of this part of the process can be found in Chapter 5. The digested food at this stage is called chyme. the walls of the esophagus alternately constrict and relax to move the bolus of food toward the stomach. It consists of a combination of ingested food. When nutrients leave the digestive tract. It is pushed down the esophagus by waves of contraction called peristalsis. A large amount of mucus present in the stomach protects the cells of the stomach lining from this acid. The contents of the stomach are squirted into the small intestine at regular intervals. including disaccharides.3 dIgestIon and nutrItIon starches. protein fragments. Nearly all the absorption of nutrients occurs in the small intestine. The liver is an accessory organ to the digestive tract that regulates much of what is removed from the blood. Additional digestive juices enter the small intestine from the pancreas and gallbladder.3 (opposite page) With swallowing. . The stomach acts as a blender. and stomach juices. mixing the food with digestive juices secreted by specialized cells in the stomach lining. One of the digestive chemicals produced in the stomach is hydrochloric acid at a concentration strong enough to eat away shoe leather. The nutrients are then absorbed into the lining cells. food leaves the mouth and enters the esophagus. A detailed description of this part of the process can be found in Chapter 5. saliva. Most of the water that enters the digestive tract with food or from the digestive juices of the stomach and pancreas is actively removed from the tube by the large intestine. Locally produced hormones control this process. occurs at the surface of the columnar cells lining the tube. and triglycerides. The final breakdown of the ingested food. Bile from the gallbladder aids in the absorption of fats in the small intestine. The esophagus transports the bolus of food to the stomach. and elimination 3 . absorption.digestion. this basic unit is a monosaccharide. Each type of nutrient has a basic building block that can be absorbed. Whatever has not been broken down or absorbed in the digestive process is eliminated through the rectum and the anus. The large intestine salvages most of the water from the intestinal contents and prepares the solid waste for elimination. A large number of goblet cells located in this portion of the tube produce the mucus necessary to move the feces through the rest of the tract. ConneCtions Nutrients must be broken down to a size that allows them to be absorbed into a microscopic cell. Lipids in the form of triglycerides are broken into glycerol and fatty acid chains. The mouth and esophagus ingest and transport food. this is an amino acid. muscularis. The final breakdown of the food is completed in the small intestine where nutrients are absorbed. This is discussed further in Chapter 6. For proteins. and the stomach blends it with digestive juices. while cholesterol is absorbed intact. and a connective tissue covering called a serosa or adventitia.40 dIgestIon and nutrItIon removal of most of the water from the digestive tube creates the material that is eliminated from the body in the form of feces. For sugars. . submucosa. The wall of the digestive tract is made up of four major layers: mucosa. Each section of the digestive tube has specific functions. Chewing starts the breakdown of food to a manageable size that can pass into the cells lining the digestive tube. The lips have a circular skeletal muscle called the orbicularis oris. eventually. The 41 . The skin at the edges of the lips is thin. Other teeth called canines.5 Chewing and Swallowing Digestion starts when Amy takes a bite of her burger. or eyeteeth. from side to side. toward the back of her mouth so she can swallow the bolus. and swallows it. and. teeth called premolars and molars grind the food. With the help of the tongue. The oropharynx is where both food and air pass to enter the digestive tube and respiratory tract. This bolus is a mixture of saliva and the ingested food. as in a pucker or a smile. MoUTh The mouth starts with the lips in front and extends back to an area called the oropharynx. Her tongue moves the food around in her mouth. When Amy bites into her burger and bun. now a pulpy mass. help her tear up some of the food. While Amy chews. or a bolus. is formed into a rounded lump. teeth called incisors cut it into bite-size pieces. the food. allowing the natural red coloring of blood to tint the lips. chews. which allows lip movement. respectively. and generally finish growing at about two years. lips do not have any sweat glands.1 Humans are born with two sets of teeth: (a) deciduous (milk) teeth and (b) permanent teeth. which are gradually replaced by the permanent teeth. so they must be moistened on a regular basis or the skin may become dry. crack. . and possibly bleed. the deciduous teeth erupt from the gums around six months of age. at about age . children begin to lose their baby teeth.42 dIgestIon and nutrItIon figure 5. The first set of teeth consists of 8 incisors. preventing a person from inhaling and swallowing at the same time. when the wisdom teeth have emerged. Humans are born with two sets of teeth hidden in the upper and lower jaws.Chewing and swallowing 43 The sides of the mouth. of the mouth is called the palate. but kept moist by saliva. This muscle helps move food around in the mouth and also helps in forming facial expressions. called permanent teeth. 4 canines. the . The front part of the roof of the mouth is the hard palate and has bone above the tissue lining the mouth. the crown. totaling 32 teeth (Figure 5. contain a skeletal muscle called the buccinator. A complete set of permanent teeth consists of 8 incisors. If it is damaged. This type of epithelium is discussed in Chapter 4. 8 premolars. At about six months of age.1a). 4 canines. fingerlike projection of the soft palate at the rear of the mouth is called the uvula. The enamel cannot be replaced. called baby teeth.2). A small. The visible part of the tooth. The permanent teeth continue to emerge up to about age 25. The first set of teeth continues to penetrate through the gums up to about two years of age. the tongue presses against the hard palate. or roof. so it is not dry. TeeTh Amy’s teeth. not bone. and 8 molars (Figure 5. or cheeks. above the mouth lining. The second set of teeth. children begin to get their first teeth. is covered with hard enamel. The inside of each cheek is covered with a stratified squamous epithelium that is not keratinized like skin. The rear portion of the roof of the mouth is called the soft palate and has skeletal muscle. When a person chews and forms certain speech sounds. begins to push the baby teeth out when a child is about 7 years of age. until all 20 teeth have emerged. or deciduous teeth. The soft palate rises during swallowing to block the opening to the nasal cavity at the top of the oropharynx.1b). The top. are her second set of teeth. and 12 molars. just as with all adults. All teeth have basically the same structure (Figure 5. More of this portion of the tooth may be . the root contains blood vessels and nerves. which lies above the gum.44 dIgestIon and nutrItIon figure 5.2 teeth are made up of two sections: the crown. the crown covers the dentin. underlying tissues of the tooth may be exposed. which reaches into the root cavity. The neck of the tooth starts at the gum line and extends through the gum. and the root. canine. resulting in the degeneration and loss of the entire tooth. which lies below the gum. The shape of the crown determines whether the tooth is an incisor. or molar. individuals perceive a fifth taste that is stimulated by an amino acid called glutamate. Some of the papillae contain taste buds. in the oropharynx. The tonsils are aggregates of lymphoid tissue that screen the incoming food for microorganisms that might attack the body. At the back of the mouth. extends through the crown. These muscles are not attached to bones. are used to change the tongue’s location. blood vessels. dentin can. the lymphocytes in the tonsils make antibodies that help defend the body from attack. Some of the skeletal muscles in the tongue are used to change its shape. and root of the tooth and makes up the bulk of the tooth. Below the neck. but are contained completely within the tongue. If these organisms are detected. which are attached to the bones of the skull and in the neck. sour. and nerves. Although enamel cannot be replaced. Other muscles. a mixture of connective tissue. ToNgUe The tongue moves the food around in the mouth. found in some foods as well as in the seasoning monosodium glutamate.Chewing and swallowing 45 exposed as the gum recedes with age. salty. Depending on the type of tooth. can hide in the tonsils and cause . so some repair of damage or decay takes place throughout a person's lifetime. forming the bolus of food and saliva. The tongue is also involved in speech. which are sensitive to tastes of sweet. neck. Dentin. a bonelike substance. or MSG. Some bacteria. the root of the tooth is embedded in the jawbone. and bitter. The surface of the tongue has projections of tissue called papillae. The central core of each tooth is filled with pulp. This pulp extends through the tooth to the base and forms the root canal. such as Streptococcus. teeth may have from one to three roots. Tonsils are found on the rearmost area of the tongue and in the surrounding soft tissue of the oropharynx. The root is held in place by a calcified type of connective tissue called cementum that attaches the tooth to a periodontal ligament. once the enamel is damaged. Plaque provides a safe haven for bacteria to live and metabolize the bits of trapped food. but still fairly large. This breaks the food into smaller. the bacteria break down the proteins of the tooth and cause tooth decay or cavities. these infections can be quite painful. and chew food. trapped sugars. may damage the seal between the tooth and the gums. the muscle that provides most of the force in biting. Most of the saliva is secreted by three pairs of salivary glands: the parotid. these bacteria continue to hide in the tonsils and cause infection again. SALivA As stated earlier. . digestion is a process that breaks down food to sizes that can be absorbed by cells. called tartar or calculus.4 dIgestIon and nutrItIon recurring throat infections. and mouth debris—sticks to teeth. These glands are found under the tongue and in front of the masseter muscle . submandibular. In extreme cases. chunks. If the infection is not treated properly. the sublingual glands produce a very mucoid secretion. The physical aspects of digestion in the mouth occur when we bite. The parotid glands produce a watery secretion. There are two components to the process: physical and chemical. Periodontal disease may result if the plaque builds up on the gums. this buildup. The combination of secretions from these YOUR HEALTH: THE IMPORTANCE OF BRUSHING YOUR TEETH tooth decay begins when dental plaque—a layer of bacteria. tear. and the submandibular glands make a combination of a watery and mucoid secretion. allowing bacteria to get into the gums and cause serious infections. Chemical digestion in the mouth involves saliva. and may sometimes lead to loss of the affected tooth or teeth. they may also be life-threatening. Bacterial waste consists of assorted acids that damage tooth enamel. and sublingual. serves as a passage for both air and food. Two enzymes in the saliva begin the chemical breakdown of food: amylase and lingual lipase. is exclusively part of the respiratory tract. In addition. phAryNx The oropharynx. Sometimes. the nasopharynx . at the back of the mouth.Chewing and swallowing 4 glands makes up normal saliva. The area above the oropharynx. The goblet cells secrete mucus that helps the bolus of food get to the esophagus and stomach. The area immediately below the oropharynx. Amylase starts the digestion of starch by breaking down the complex structure of starch molecules into smaller combinations of glucose units that are separated further along the digestive tube. The muscularis . the salivary glands will release saliva. If a person is dehydrated. and starting the chemical digestion of starches and some lipids. This epithelium has the first goblet cells found in the digestive tube. The oropharynx and the laryngopharynx are lined with stratified squamous epithelial cells to protect the underlying tissue from damage. the thought or smell of food will result in saliva release. such as excess acids or bacterial toxins. including cleansing the mouth. Because amylase works at an alkaline ph. if the small or large intestine is irritated by some substance. is just one of three parts of the pharynx . A person produces about 1 to 1. the saliva produced is thick and comes mostly from the sublingual glands. dissolving food to enhance taste. such as vinegar or citric juices. the laryngopharynx . Lingual lipase is a form of lipase that separates triglycerides into their components of glycerol and fatty acids. Saliva has several purposes. The salivary glands produce saliva when stimulated by the presence of food in the mouth or by certain acidic foods. saliva contains bicarbonate to maintain these conditions.5 liters) of saliva per day. moistening food to form a bolus.5 quarts (about 1 to 1. 4 dIgestIon and nutrItIon layer of the pharynx has two layers of smooth muscle.3 illustrates the anatomy of both the pharynx and the esophagus. the inner layer is longitudinal and the outer layer is circular. . The two layers work together to propel food by peristalsis to the stomach. figure 5. Figure 5.3 structures of the pharynx and esophagus. but in the opposite arrangement from that found throughout the rest of the digestive tube. the esophagus connects the pharynx to the stomach. Here. which is called the cardiac sphincter. closing off the windpipe. usually made up of smooth muscle cells. The presence of the food in the esopha- . the inner circular and the outer longitudinal. When a person swallows. The larynx rises. The esophagus is made up of four layers of tissues.) The cardiac sphincter loosely controls the opening of the esophagus into the stomach. causing a lid-shaped piece of cartilage and soft tissue called the epiglottis to cover the opening to the trachea. The esophagus is about 10 inches (25. This muscle assists the cardiac sphincter in limiting access to the stomach.Chewing and swallowing 4 eSophAgUS Once the bolus of food passes through the oro. that opens and closes a tube. First. Finally. The first third of the esophagus has skeletal muscle in the muscularis layer. the last third has smooth muscle. The muscularis has two layers of muscle. the mucosal and submucosal layers of the esophagus fold along the length of the tube when it is empty. (A sphincter is a circular muscle. the soft palate rises to close the connection with the nasal passage. SWALLoWiNg Swallowing is actually a complex process. Then. a series of reflexes occur that ensure that the action occurs properly. Next. located behind the windpipe. the innermost layer. The esophagus passes through the diaphragm located just above the stomach. as in the mouth and pharynx. is collapsed when empty. starts at the bottom of the laryngopharynx. the tongue blocks the possibility of reentry of the food into the mouth. and the middle portion has a mixture that gradually goes from skeletal to smooth muscle cells. is made up of stratified squamous cells. This muscular tube.4 cm) long. The epithelial lining.and laryngopharynx. it enters the esophagus. the esophagus has an outer layer called the adventitia that blends the tube covering with the surrounding tissue and holds the esophagus in place in the throat. and ends at the opening of the stomach. but not all of the muscle is the same type. Solid food passes to the stomach in 4 to 8 seconds. and grind food and saliva into a paste. this regurgitation can occur when a person vomits. When food is swallowed. All teeth have a common structure and have hard enamel to protect underlying tissues from decay and damage.50 dIgestIon and nutrItIon YOUR HEALTH: HEARTBURN heartburn occurs when the stomach contents pass back up into the esophagus. tear. or running. Further digestion is necessary and continues in the stomach and small intestine. It is fairly easy to overcome these barriers and bring stomach contents back up into the tube. If this occurs. . gus stretches the tube and causes the muscle contractions that result in peristalsis. the acid burns the epithelial layers of the esophagus and may cause scarring of the tissue. the bolus no longer resembles the food it started out as. Baby teeth start erupting from the gums at about 6 months of age and begin to be replaced by permanent teeth at about 7 years of age and continue to age 25. ConneCtions Digestion starts with the first bite of food. The nutrients have been partly digested. the cardiac sphincter and the diaphragm do not entirely close off the connection to the stomach. the esophagus does not fold when empty or propel food properly through peristaltic contractions. the stomach is overfull. or a person is obese. liquids in 1 to 2 seconds. the scarring also leaves the tissue susceptible to further damage due to the loss of the stratified epithelial layers that protect the underlying tissue. or about the strength of a car’s battery acid. Because the pH of the stomach fluids is usually below 4. pregnant. but they are still not ready to be absorbed into the body. Teeth cut. as will be described in the next chapter. floor. palate. The tongue helps to manipulate food during chewing. The saliva produced by salivary glands moistens the food and begins the chemical digestion of starches and triglycerides. in the form of a bolus. . and it is also essential in speech. Food.Chewing and swallowing 51 The mouth is bordered by the lips. Taste buds on the tongue are stimulated by different chemicals. cheeks. and pharynx. The process of swallowing is a reflex that propels food and prevents it from entering the respiratory tract. passes from the mouth to the pharynx and into the esophagus for passage to the stomach. 1) and turns the bolus of food into chyme. The stomach. The positioning of these layers allows the stomach to constrict in all directions. The muscularis in the stomach consists of three distinct layers. In the innermost layer. all of the nutrients that can be absorbed into the lining cells of the digestive tube will be absorbed.6 The Stomach and Small Intestine The bolus of food that enters the stomach contains some partially digested food and some food that has not been broken down at all. The outermost layer runs longitudinally. Below the esophagus. which is really a section of the digestive tube. The largest part of 52 . the stomach works to digest proteins in the food (Figure 6. making it look similar to a donut. is shaped somewhat like the letter J. Digestion of protein begins in the stomach. Before they leave the small intestine. Amylase and lingual lipase begin the digestion of starch and triglycerides. respectively. the fibers are oblique to the other layers The middle layer is arranged in a circular pattern. SToMACh The connection between the stomach and the esophagus is called the cardiac sphincter. three layers of smooth muscle make up most of the wall of the stomach. the body. The portion of the stomach above the body but below the connection to the esophagus is called the .the stomach and small Intestine 53 figure 6. is where most of the stomach’s digestive activity occurs.1 the stomach is located below the diaphragm. It connects to the esophagus at the cardiac sphincter and to the duodenum of the small intestine at the pyloric sphincter. the stomach. Folds of the mucosa called rugae increase the surface area of the organ. some of it stays in the fundus while the rest is mixed with stomach fluids.2). As the food in the body of the stomach leaves to enter the small intestine. A third type of cell found in the epithelia of the gastric pits is the chief cell. Parietal cells also secrete a chemical called intrinsic factor that is necessary for the absorption of vitamin B12 in the small intestine. When pepsinogen comes in contact with hydrochloric acid.54 dIgestIon and nutrItIon fundus. In this way. When food enters the stomach. it is converted into an active enzyme called pepsin. Pepsin begins the digestion of proteins by breaking large. more food is brought from the fundus to continue the digestive process. While the food is in the fundus. complex proteins into smaller molecules that will be further . while a full one is considerably larger. The epithelial cells extend into the underlying layers of the mucosa to form depressions called gastric pits (Figure 6. These folds expand the surface area of the inside of the stomach. When the stomach is empty. The acid digests everything. the fundus acts like a storeroom for excess food until there is space in the body of the stomach. especially after a large meal. especially the hydrochloric acid secreted by the parietal cells. large folds called rugae are created in the mucosa that can be seen without magnification. Goblet cells secrete mucus to protect the stomach lining from other secretions. The acid aids digestion by indiscriminately breaking up larger compounds into smaller ones. salivary amylase continues to break up starch. If intrinsic factor is not available. The mucosa of the stomach has several adaptations not found anywhere else in the digestive tract. These pits are lined with a mixture of columnar epithelial cells and special cells that secrete chemicals to aid in digestion. This cell secretes a chemical called pepsinogen. including bacteria and medications. An empty stomach is about the size of a fist. the vitamin is not absorbed and a syndrome called pernicious anemia results. If hydrochloric acid is not present. called the G cell. broken down in the small intestine. secretes a hormone called gastrin that is primarily responsible . The fourth specialized epithelial cell. pepsin will not be formed from pepsinogen and the digestion of protein will not begin.2 gastric pits.the stomach and small Intestine 55 figure 6. found in the lining of the stomach. a micrograph of gastric pits shows the cells up close. contain special cells that secrete chemicals used in digestion. In addition to the action of the stretch receptors. the acidic stomach contents. regULATiNg DigeSTioN iN The SToMACh Digestion in the stomach can be stimulated in a variety of ways. this control process includes the neutralization of stomach acid. When food enters the stomach. certain chemicals. Stomach digestion is also slowed by the actions of the small intestine. caffeine. such as caffeine and alcohol. These nerves relay a signal that stimulates gastrin secretion. In addition to continuing digestion in the intestine. Few materials are absorbed through the stomach lining. slowing production of pepsin and slowing down the initial breakdown of proteins. specialized nerves within the smooth muscle layers of the stomach. sight. cause stomach fluids to be produced. resulting in pressure on stretch receptors . The interaction of the stomach and small intestine ensures that the small intestine receives chyme in amounts that it can handle. The stomach functions to prepare food for further digestion and absorption in the small intestine. Stomach fluids are produced when the G cells are active. it stretches the walls of the stomach. The thought. The presence in the small intestine of protein fragments called peptides and fatty acids from triglyceride breakdown also inhibits the nervous system's stimulation of the G cells and slows the mixing of the stomach contents. and . or smell of food can stimulate the stomach to secrete digestive fluids. The hydrochloric acid would harm the intestinal lining and cause a type of ulcer (see the “Your Health” section concerning ulcers on page 58). When chyme.5 dIgestIon and nutrItIon for stimulating the other three types of cells. Glucose. enters the small intestine. Increasing amounts of hydrochloric acid in the stomach cause the parietal cells to decrease secretion of the acid. the nervous system stimulation of the G cells is inhibited. Highly alkaline food also causes stomach secretions to flow. The small intestine does not have the relatively thick protective layer of mucus found in the stomach. and twisted to fit into the abdominal cavity. and the ileum. Chyme from the stomach enters the duodenum portion of the small intestine. digestion is completed. which is about 10 inches long. The products of digestion are absorbed through the digestive tube lining and transported to the rest of the body’s tissues by the blood and lymphatic vascular systems. It may take hours to empty the stomach after a big meal. the pyloric sphincter regulates the amount of food that enters the small intestine. the jejunum. Water is absorbed in the stomach only if it contains a sufficient amount of dissolved glucose. Its opening and closing is controlled by the amount of food in the stomach and by feedback from the small intestine. the ileum. about one ounce of fluid at a time. The adaptations of the digestive tube wall in the small intestine involve the mucosa and submucosa. thereby . the pyloric sphincter cannot be easily forced open. is about 6 feet long. The last portion of the small intestine.the stomach and small Intestine 5 alcohol are three chemicals that are absorbed through the stomach lining. SMALL iNTeSTiNe In the small intestine. Both of these effects increase the contact of the tube’s contents with the epithelial layer. At the junction of the stomach and the small intestine. The jejunum. The small intestine has three sections: the duodenum. Unlike the cardiac sphincter. The small intestine is bent. The stomach empties slowly. or middle segment of the small intestine. folded. into the small intestine. The formulation of sports drinks for athletes takes advantage of this dual absorption to rapidly increase the body’s energy supply for muscle metabolism and to rehydrate the body after extensive sweating. is about 3 feet long. The mucosa is folded into circular folds that increase the surface area of the small intestine and force the intestinal contents to go through the tube in a spiral pattern. treatment usually involved removing the damaged part of the stomach. Currently.5 dIgestIon and nutrItIon increasing the chances of nutrients being absorbed into the lining cells.to 14-day supply of two antibiotics and a bismuth compound to enhance healing of the stomach “sore. the microorganism also makes enzymes that damage the mucosa and allow the hydrochloric acid to further damage the stomach lining in areas where ammonia is not present. a hole may be created in the wall of the stomach that would allow food and microorganisms access to the abdominal cavity. When a person has a gastric or peptic ulcer. ulcers were believed to be caused by stress. alcohol use. pylori burrows under the mucus layer in the stomach and produces ammonia. YOUR HEALTH: ULCERS Imagine the body attacking and damaging its own tissues. a bacterium called Helicobacter pylori is now believed to be the primary cause of ulcers and the cause of their recurrence. this damage to the mucosa may go through the lining to the blood vessels in the submucosa and result in significant bleeding in the digestive tract. or use of excessive amounts of aspirin. .” the antibiotics kill the bacteria while the bismuth salicylate protects the stomach lining from acid and inhibits growth of the bacteria. 5% of ulcers recurred. aspirin and other nonsteroidal anti-inflammatory drugs. are still believed to be a cause of ulcers. such as ibuprofen. resulting in a lifethreatening infection called peritonitis. this may lead to bleeding so severe that it compromises the body’s ability to deliver adequate oxygen to tissues. such bleeding results in severe anemia. until the 10s. but they are not the most common cause. damaging the mucosa. the hydrochloric acid attacks the walls of the stomach. ulcers are treated by giving the person a 10. If the damage is severe. which neutralizes stomach acid in the small area surrounding the bacteria. H. Before the bacterium was identified as the cause of ulcers. The membrane of each mucosal epithelial cell has projections from the surface called microvilli (Figure 6. The jejunum has no specialized microscopic adaptations in its submucosa. The Brunner’s glands secrete an alkaline mucus that helps to neutralize the acidic chyme from the stomach. The adaptations in the submucosa help to identify the three portions of the small intestine. The center of each villus contains two capillaries: a blood capillary and a lymphatic capillary. These fats are sent around to the body and are used by the body’s tissues as a source of energy or as structural materials needed for growth or repair of body tissues. . and ultimately into the blood. The fats in the lymphatic capillaries do not go directly to the liver.3). All blood drained away from the digestive tract goes directly to the liver. The ileum has clumps of lymphoid tissue called peyer’s patches in its submucosa. The duodenum has glands called brunner’s glands in the submucosa. enter the lymphatic capillary. This lymphoid tissue helps to screen the ingested material in a way similar to what the tonsils do. such as cholesterol and triglycerides. the liver is the body’s chemical processing plant and uses the nutrients from digestion for multiple purposes. The lymphatic capillary contains a fluid called lymph that will pass into the lymphatic system.the stomach and small Intestine 5 The mucosa also has fingerlike projections called villi. As will be discussed in Chapter 6. enter the blood capillary. These projections are a third way of increasing the surface area of the small intestine to aid in the digestion and absorption of digested material. The blood capillary contains blood and connects an artery to a vein. but are dumped into the bloodstream by way of the jugular and subclavian veins in the neck. such as sugars and amino acids. Materials that have been absorbed into the digestive tube’s lining pass into one of these capillaries. while fat-soluble material. which greatly increase the surface area for absorption. Water-soluble materials. 0 dIgestIon and nutrItIon . insulin and glucagon are two pancreatic hormones that work within the body to control blood glucose levels. . thus increasing the potential for nutrient absorption. which contains some mucus. which is stored in the gallbladder. The hormone cholecystokinin (CCK) causes the gallbladder to constrict and pump figure 6. The intestinal juice. About 1 to 2 quarts (1 to 2 liters) of this digestive fluid is produced each day. In addition. The chyme also causes the release of two hormones from the duodenum. The liver has several important functions in the body. a waste product of dead red blood cells. and bicarbonate to deliver to the duodenum to help digestion. helps digestion by emulsifying fats into smaller molecules for absorption. protein. Bile is composed of bile salts . Villi are fingerlike projections on the surface of the intestine. It regulates carbohydrate.the stomach and small Intestine 1 ACCeSSory orgANS: The Liver. causes cells at the beginning of the duodenum to secrete intestinal fluid. and microvilli are smaller projections stemming from the villi. the liver eliminates bilirubin .3 (opposite page) Villi and microvilli act to increase the surface area of the small intestine. it triggers several events. The pancreas produces hormones. When needed. DigeSTioN iN The SMALL iNTeSTiNe When acidic chyme enters the duodenum. and lipid metabolism and detoxifies body wastes and drugs that have entered the body. This fluid. by incorporating it into bile. and phospholipids. along with protein fragments and fatty acids in the chyme. digestive enzymes. The acid. AND pANCreAS The liver and the gallbladder are two important accessory digestive organs that work with the small intestine. is alkaline and helps to neutralize the acidic chyme and protect the duodenum from the effects of the acid. gALLbLADDer. bile is released from the gallbladder into ducts that connect to the small intestine. as well as other substances. cholesterol. triglycerides. but not into glucose molecules. the body has found an alternate way to transport fat droplets into cells. these droplets are then digested by enzymes called lipases and eventually form micelles. These include trypsin. and nucleic acids into intermediate-sized molecules. The bicarbonate neutralizes most of the hydrochloric acid from the stomach. the disaccharides. The nucleic acids. have not been broken down.2 dIgestIon and nutrItIon bile into the small intestine via the bile duct. CCK also causes the pancreas to secrete digestive enzymes into the duodenum. peptides. the small intestine contents are alkaline. thus. figure 6. the lipids combine with bile salts to form emulsion droplets. Digestive enzymes break starch. are broken into nucleotides (their building blocks) by enzymes called nucleases. which are short chains of amino acids. and carboxypeptidase. which can pass into the cell. The peptides that are formed as a result of the action of these enzymes are structurally very short and will be further broken down at the surface of villi and microvilli. Pancreatic amylase breaks down starch into smaller pieces. and nucleotides into their most basic components. After the neutralization occurs. they cannot easily diffuse across cell membranes. DNA and RNA. including the disaccharide maltose. such as sucrose (from table sugar and fruits) and lactose (from milk) that are ingested. The hormone secretin causes the pancreas to secrete large amounts of bicarbonate into the small intestine. The final digestion of material occurs at the villi. . proteins. First. Enzymes from the epithelial cells of the villi break down disaccharides. chymotrypsin. by several pancreatic enzymes that are collectively called peptidases. Dietary triglycerides are broken apart by pancreatic lipase. Thus far in the digestive process. elastase. The nucleotides will also be further digested at the surface of the villi.4 (opposite page) Because fats are not water soluble. Proteins are broken into peptides. creating the conditions needed for the digestive enzymes to work. the stomach and small Intestine 3 . Bile salts combine with these fats to form tiny spheres called micelles (Figure 6. they have been combined with cell proteins that help carry them in the lymph and blood.1 summary orgAN Mouth of THe dIgesTIVe proCess Digests starch Digests triglycerides Protects stomach lining Converts pepsinogen to pepsin: As pepsin. This combination of cholesterol.4). and lining cell proteins is called a chylomicron. By the time the fats leave the lining cells. The chylomicrons will circulate in Table 6. triglycerides. This material passes through the lining cell membranes and into the blood capillaries of the villi almost immediately. Cholesterol and long-chain fatty acids cannot diffuse through the cell membranes and must be handled differently. These spheres can pass through the cell membranes and transport the fats into the cells. Glycerol and short-chain fatty acids from triglycerides are absorbed by simple diffusion across the cell membranes in the digestive lining.4 dIgestIon and nutrItIon which makes them suitable for absorption. Lipid absorption is a more complicated process. This process works very efficiently because the final breakdown of nutrients occurs at the exact site of nutrient absorption. digests proteins Emulsifies fats Digests starch Digests triglycerides Digests nucleic acids Digests proteins Final steps in digestion SoUrCe: eNzyMeS/CheMiCAL ACTioN Saliva: Amylase Saliva: Lingual lipase Stomach Goblet cells: Mucous Parietal cells: Hydrochloric acid Chief cells: Pepsinogen Gallbladder Pancreas Bile salts Amylase Lipase Nucleases Peptidases Villi Assorted enzymes . 1 quart of saliva. 1 quart of bile. other materials are also absorbed through the lining of the small intestine. In addition to the nutrients discussed. and some water leave the small intestine and enter the large intestine.the stomach and small Intestine 5 the blood. calcium. but most of it enters into the system at various points during the digestive process to aid in the breakdown of food. About 9 quarts (8. magnesium. waste. Any leftover nutrients. The three layers of smooth muscle in the muscularis allow the stomach to compress its contents in all directions.5 liters) of water enter the small intestine each day. Eventually. and a chemical to aid in vitamin absorption. Digestive functions in the stomach are controlled by hormones secreted by the lining cells and by hormones (continues) . nitrate. potassium. carrying triglycerides to body tissues. The lining of the stomach contains specialized cells that secrete digestive enzyme precursors. 2 quarts of stomach (gastric) juices. 2 quarts of pancreatic juice. including the electrolytes sodium. acid. Much of the water that enters the large intestine is reabsorbed into the blood so that very little is excreted in the feces. Most of the water is reabsorbed through the small intestinal walls. Table 6. the chylomicron remnants will be picked up by the liver. The digestion of starch is halted by the hydrochloric acid in the stomach. and phosphates. The source of these fluids is approximately as follows: 1 to 2 quarts with food. and bicarbonate and trace elements such as iodate. chloride. iron. and 1 quart of intestinal juice. Some of this water is ingested with food (like Amy’s chocolate shake).1 summarizes the process of digestion. ConneCtions A bolus of food and saliva enters the stomach and is combined with digestive juices that are a mixture of strong acid and enzymes that begin the breakdown of proteins and lipids. blending the nutrients with digestive juices. proteins and lipids. and ileum. Structures found in the submucosa differentiate the three portions of the small intestine. The mucosa of the small intestine has villi that increase the surface area of the tube and provide the enzymes necessary for the final steps of digestion. . and bile to assist in lipid absorption. The small intestine is divided into three parts: the duodenum. jejunum. Few materials are absorbed through the stomach lining. enzymes to break down carbohydrates. These juices contain bicarbonate to neutralize stomach acid. Digestive juices are secreted into the duodenum from the gallbladder and pancreas. dIgestIon and nutrItIon (continued) originating in the first part of the small intestine. Vitamin K. These bacteria make vitamins that are absorbed and used by the body. but a type of digestion still takes place in the large intestine. various parts of the body can bleed two to three days after the bacteria are removed. About 1 quart (1 liter) is left and all but about 3 to 4 ounces (90 to 120 milliliters) of this water will be absorbed by the large intestine. The bacteria also make a variety of B vitamins that are used in the metabolism. is used by the liver to make proteins that play a role in blood clotting.7 The Large Intestine and Elimination The chyme that enters the large intestine is different from the chyme that enters the small intestine. Most of the 9 quarts (8. Vitamin K is so important to us that if these bacteria are removed by diarrhea or excessive antibiotic use. All of the nutrients that can be absorbed from the food have been absorbed.5 liters) of water that were present in the small intestine have also been removed by this point. producing the feces that will be eliminated from the body. which is one of those vitamins. Large numbers of bacteria that live in the large intestine finish digesting the chyme and use the nutrients for their own metabolism and growth.  . is about 3 inches (7. There are four major sections of the large intestine: the cecum. rectum. The cecum. It is wider than the previous sections of the digestive tube and can store material for 12 to 24 hours until elimination.5 meters) long and 2. shorter.1) is a tube about 5 feet (1.6 cm) long. On the left side of the abdomen is the descending colon. which is on the right side of the abdomen. It is open to the cecum at one end and closed at the other end. After chyme leaves the cecum. colon. section of the large intestine is the colon. which connects to the small intestine. The appendix has no function in digestion or absorption.4 centimeters) in diameter. . If the appendix bursts. which is attached to the cecum. the longest part of the large intestine. This section is divided into four regions based on the direction or shape of the tube. is a 6-inch-long (15 cm). it goes into the ascending colon. The colon begins to twist and bend down toward the middle of the body at this point. The large intestine is connected to the small intestine by the ileocecal valve. causing acute infections that are difficult to treat and may lead to death. dIgestIon and nutrItIon LArge iNTeSTiNe ANAToMy AND DigeSTioN The large intestine (Figure 7. parts of the large intestine. but has several large aggregates of lymphoid tissue and may play a role in the immune system. pouch-shaped portion of the tube that stores small amounts of chyme until it passes into the colon. The appendix can easily be twisted or blocked. the bacteria that inhabit the large intestine can gain access to the abdominal cavity. The appendix. This portion is called the sigmoid colon and the twisting brings the tube in line with the last two. The part of the colon that is in front of the stomach just under the diaphragm is called the transverse colon. and largest. causing an inflammation called appendicitis. The second. and anal canal. the rectum and the anal canal.5 inches (6. the Large Intestine and elimination  figure 7.1 the large intestine consists of the cecum, colon, rectum, and anal canal. It is the last place where the body will remove nutrients before the waste is excreted. There are several differences between the walls of the small and large intestines. First, the mucosa of the large intestine has no villi. The mucosal epithelium is made up of columnar cells and goblet cells. The mucus-secreting cells increase in number throughout the large intestine, which, in 0 dIgestIon and nutrItIon turn, increases the amount of mucus secreted. The mucus assists the passage of intestinal contents that are becoming increasingly dehydrated. The muscularis contains two layers of smooth muscle, but the outer layer is made up of three bands of muscle called the teniae coli. The regular constrictions of the teniae coli result in a muscle tone that gives the appearance of a series of pouches, or haustra, along the colon. The large intestine appears as though a piece of string were loosely tied around the diameter of the tube every couple of inches. As chyme travels through the large intestine, it moves from haustra to haustra with some mixing and storage at each stop. This process is called haustral churning and results in the physical digestion that occurs in the large intestine. As stated above, the chemical digestion that occurs in the large intestine is carried out by bacteria. These microorganisms are collectively called normal flora because they are normally found in the colon. E. coli, a bacterium that has received a lot of attention, is one of the organisms that normally exist in the large intestine. (It does not, however, normally exist in the urinary tract, where it is the most frequent cause of urinary tract infections.) The end of the intestinal tract is the anus, which is not far from the urethra, the opening for voiding urine. The transfer of bacteria from one opening to the other can result in a painful urinary tract infection. The intestinal bacteria use whatever carbohydrates have not been absorbed in the small intestine. The bacteria produce waste material that includes gases such as hydrogen, nitrogen, methane, carbon hydroxide, and dimethyl sulfide. About 1 pint (0.5 liter) of this gas is produced daily. The last component, dimethyl sulfide, is responsible for the strong odor of these gases. Some acids will also be produced and, in higher than normal concentrations, may cause abdominal pain and increase motility, or moveability of materials, in the large intestine, resulting in diarrhea. the Large Intestine and elimination 1 The bacteria also convert any amino acids that enter the large intestine into fatty acids and pass them in the feces. The bacteria convert bilirubin from the liver into a chemical called stercobilin, which produces the normal brown color of feces. If there is no bile coming from the liver or gallbladder, the feces are white or gray colored, and usually high in undigested fats because bile was not present to emulsify digestive fats. This whitish coloring and increased fat content indicates gallbladder problems. A person can live without the large intestine. In cases of cancer of the digestive tract, the large intestine can be removed and the person’s intestine attached to an opening in the abdominal wall. Feces are collected in a bag attached to the outside of the abdomen. This procedure is called a colostomy. Care must be given to supply the vitamins that are usually absorbed from the large intestine. DefeCATioN Defecation is the process of eliminating feces. Feces enter the rectum, which is about 8 inches (20 cm) long, and travel to the anal canal. The anal canal is short, about 1.5 inches (4 cm) long, and ends at the body opening called the anus. There are two muscle sphincters in the anal canal, one at the beginning and one at the end. They are both involved in the elimination of feces. By the time the content of the digestive tube has reached the anal canal, it is made up of 2 to 3 ounces (60 to 90 milliliters) of water, a mixture of inorganic salts, dead epithelial cells, bacteria (about 30% by weight), unabsorbed material, and undigested material. Defecation results from the movement of chyme/feces through the large intestine by mass peristaltic movements during the day, building up feces in the rectum. The feces cause the rectal wall to stretch, resulting in initiation of the defecation reflex. This reflex involves local nerves and the two sphincters of the anal canal. The sphincter at the begin- soluble types of fiber are found in beans. which helps to decrease the cholesterol in the body and lower the risk of heart disease and stroke. two-thirds of the cholesterol that enters the intestine is reabsorbed. ordinarily. When children become “potty trained. DiArrheA Diarrhea. the frequent elimination of fluid feces. Fiber keeps cholesterol in the digestive tube until elimination. and colorectal cancer. the signal is not received in time to voluntarily keep the second sphincter closed. allowing feces to enter the anal canal. and citrus fruits. In the case of an infant human. local nerves send a signal to the brain of the need to have a bowel movement. there are two types of fiber: soluble and insoluble. . made of skeletal muscle. Increased fiber in the diet also decreases the risk of developing obesity. barley. oat. apples. hemorrhoids. prunes. from teen to elderly. The defecation reflex causes this sphincter to open. diabetes mellitus. is a condition that occasionally happens to all of us. is under voluntary control and can remain closed. It can occur for a variety of reasons. A person who has become incontinent has lost the ability to keep the second sphincter closed. this fiber forms a gel that slows the movement of chyme through the intestine and binds cholesterol. this type of fiber is found in fruit skins and the bran of wheat and corn.” they are able to keep this sphincter closed until they choose to defecate. Osmotic diarrhea occurs when a large DID YOU KNOW? Fiber is important for digestion at any age. atherosclerosis. At this point.2 dIgestIon and nutrItIon ning of the canal is made of smooth muscle. broccoli. The second sphincter. Insoluble fiber speeds up motility in the intestine and helps people have regular bowel movements. Diarrhea can also occur when the mucosa becomes inflamed or damaged. The person’s tissues will become more acidic. more water than usual is retained in the tube. As stated in Chapter 6. and body proteins will not function normally. Two principal electrolytes are sodium and potassium. Whatever the cause. coli. and a related organism called Shigella cause diarrhea by this method. bicarbonate is released into the small intestine to neutralize hydrochloric acid from the stomach. This type of diarrhea can be caused by various drugs or by stress. instead of being removed.the Large Intestine and elimination 3 amount of unabsorbed material is retained in the intestine. The reabsorption of water that occurs in the intestines can be reversed by bacterial toxins. To keep this material in solution. The type of Salmonella bacteria that causes typhoid fever invades the intestinal wall. Inflammation of the digestive tube can result in large amounts of mucus and blood collecting in the intestine. If the loss is severe enough. Staphylococcus. Some of the substances lost as a result of diarrhea are electrolytes. resulting in water pouring into the intestines. If the diarrhea affects the small intestine. the acid-base balance of the blood and tissues will be affected. both damaging the wall and causing severe inflammation. Medications containing large amounts of sodium and magnesium sulfates will have this effect. Peristalsis can be increased to the extent that the chyme is forced through and out of the intestine. The microorganism that causes cholera produces a toxin that results in so much diarrhea that the person may die as a result of fluid loss. resulting in diarrhea. diarrhea results in the loss of fluid and other substances from the body. Loss of these chemicals causes electrical imbalances in the body that affect heart and nerve function. Types of E. . If the bicarbonate is not reabsorbed. necessary nutrients will be lost with the fluid. heart function will be compromised and the central nervous system will cease to work efficiently. Improper handling of food may also cause bacterial contamination. . As water is lost.to 24-hour incubation period before symptoms of severe diarrhea appear. are not cooked properly before they are eaten. the bacteria cannot grow and produce the chemical toxins that cause symptoms. resulting in death. For example. if food is left out in the summer heat. WhAT feCeS TeLL US AboUT The boDy Feces that have been eliminated from the body can be used to obtain information about the health of the person. the microorganism frequently damages the walls of the intestinal tract to the point that it can get through the lining cells and gain access to the rest of the body. the color of feces and the presence of increased fat can indicate gallbladder problems. if the infected chicken or fish is prepared on the same surface as other foods without that surface being adequately cleaned. people may become ill. This form of cancer causes bleeding into the digestive tract that can be detected in the feces.4 dIgestIon and nutrItIon Perhaps the most damaging effect of diarrhea is the loss of water. the person develops an infection of the bloodstream and possibly other organs of the body. If colorectal cancer is YOUR HEALTH: FOOD POISONING Food poisoning occurs when bacteria in food are not killed before being ingested. this type of infection can be life-threatening. which usually harbor salmonella. When this happens. it provides an ideal growth medium for staphylococcus bacteria. the bacteria can be transmitted to foods that might not be cooked to the same high temperatures as chicken. If chicken or fish. it is drawn from the body tissues to keep the blood liquid. salmonella has a 12. particularly anything containing dairy products. If food is kept refrigerated. eventually causing the body tissues to lose function and shut down completely. This material can also be used to screen for a type of malignancy called colorectal cancer. As stated above. also. and anal canal. ConneCtions Material to be digested enters the large intestine as chyme and leaves as feces. saving the person’s life. . bacteria finish digesting any nutrients that were not broken apart and absorbed in the small intestine. Colorectal cancer is the second leading cause of death in men and the third leading cause of death in women.the Large Intestine and elimination 5 detected early enough. These bacteria are normal and produce vitamins that the body needs. rectum. especially vitamin K for blood clotting. it can be eliminated. Along the way. The digestive tube of the large intestine is divided into four major parts: the cecum. colon. Lactose. most often in the jejunum. she cannot digest milk unless it is in the form of yogurt. Two common conditions are lactose intolerance and malabsorption. about 90%  . the enzyme that digests lactose. such as yogurt. or cottage cheese. This is important because the breast milk of humans contains more lactose than that of any other mammal. such as that chocolate shake she had with her lunch. most people produce lactase. hard cheese. These people can no longer tolerate milk or milk products except those that have been partially broken down. however. Drinking any milk products that contain lactose. LACToSe iNToLerANCe Because Amy has a form of lactose intolerance. the carbohydrate component of milk. lose the ability to produce lactase as they become adults. As babies. to be absorbed in the small intestine. glucose and galactose. must be broken into its two monosaccharides. In the United States. Many people.8 Common Health Problems There are many conditions that affect the way the body digests food. will result in discomfort. The bacteria also produce acid. 75% of African Americans. instant soups. cereals. The lactose that cannot be used by her body is used by the bacteria in her intestine. salad dressings. 50% of Hispanics. Drinking acidophilus milk or taking a pill containing lactase can also help avoid the digestive problems. whey (the liquid from milk). bloating. and casein. People whose ancestors depended on dairy farming tend to continue to be able to consume milk all their lives. which affects abdominal sensory nerves and causes the abdominal cramping. and 20% of Caucasians are lactose intolerant. she may experience diarrhea. Amy makes some lactase. because total absence of the enzyme is extremely rare. Biologists suggest that the persistence of the production of lactase into adulthood by some people may have occurred because of the development of dairy farming thousands of years ago. Anyone with lactose intolerance should avoid milk. a collection of conditions that cause problems in get- .Common Health Problems  of Asian Americans. which is milk protein. A short time after drinking the shake. People with lactose intolerance need to be careful not to become deficient in calcium or riboflavin. milk solids. The severity of the symptoms that Amy experiences depends on how much lactase her body makes. In addition. and abdominal cramps. Lactose is also found in breads. about 20% of prescription drugs and 5% of overthe-counter drugs contain lactose. a B vitamin. This accounts for the bloating feeling in the abdomen. MALAbSorpTioN Lactose intolerance is one of type of malabsorption syndrome. gas. instant potatoes. These bacteria ferment the sugar and produce hydrogen and carbon dioxide gases. so some of the sugar from the shake will be absorbed in the intestine. and nondairy powdered creamers. The sugar is retained in the small and large intestines and causes more water to be retained in the digestive tube than normal. such as lactose. If fats are not absorbed. and these chemicals are not absorbed. If the pancreas does not produce enough lipase. If the liver does not get enough building blocks for the proteins. or K. Malabsorption syndromes lead to deficiencies in nutrients. and they remain in the intestines and are excreted as part of the feces. neither are the fat-soluble vitamins A. deficiencies of vitamin A can result in night blindness. their concentrations. the liver makes most of the proteins found in blood. Long-term malabsorption will cause a deficiency in vitamin B12. a condition called steatorrhea. which also causes anemia. As a result. E. nutrients will not be used properly. As stated in Chapter 6. water will leave the blood and pool in body cavities. and it becomes frothy and very foul smelling. Albumin is an important blood protein in maintaining osmotic pressure between the blood and tissues. especially of albumin. The combination of inadequate amino acid absorption and insufficient iron results in iron deficiency anemia. If the gallbladder does not contribute bile to the small intestine. dIgestIon and nutrItIon ting nutrients from the digestive tract to the cells of the body. triglycerides are not broken down. Some forms of cancer and some parasitic infections can also cause these transport problems. micelles are not formed from cholesterol and long-chain fatty acids. or (4) congenital or developmental problems with the part of the circulatory system that transports absorbed water-soluble nutrients to the liver for processing (see Chapter 6). primarily in proteins and lipids. There are four kinds of malabsorption problems: (1) There can be a problem with the absorption of only one type of nutrient. If there is something wrong with this part of the circulatory system. If the albumin levels get too low. If lipids are not absorbed properly. (2) a problem with the production or delivery of gastric juices into the stomach. (3) a problem with the production or delivery of enzymes from the pancreas or bile from the gallbladder to the small intestine. D. will decrease. inadequate vitamin D will lead to decreased calcium . the volume of stool increases. and mediumlength fatty acids can be absorbed without being made into micelles.Common Health Problems  absorption and eventually to weakened bones. and abdominal distress. Therapy for malabsorption conditions depends on the cause of the problem. supplements of vitamins and trace minerals like calcium. The symptoms of malabsorption syndromes are similar and include weight loss. magnesium. ConneCtions Different conditions can affect the processing and availability of food. vitamin E deficiency can cause damage to cells from chemicals produced in metabolism. . and low levels of vitamin K can lead to bleeding due to a deficiency of blood-clotting factor. malabsorption may lead to a general failure to grow and develop normally. the body experiences problems. In very young children. Children who suffer from malabsorption may not grow to their full potential height due to inadequate nutrients during growth spurts. Short. anemia. and iron are used. Substitutions can be made for the triglycerides that cannot be absorbed. are not digested or absorbed. diarrhea. such as lactose. such as diarrhea and possibly nutritional deficiencies. If the malabsorption cannot be cured. If there is an underlying disease or abnormality. it must be addressed and the malabsorption will be eliminated. When specific types of nutrients. A third method bases obesity on a calculation called the body mass index (BMI). If a person’s body fat is more than 25% for a man or 30% for a woman. that person is considered obese.9 Guides to Healthy Eating Although the body needs nutrients from a wide variety of foods. This index calculates a 0 . Obesity can be measured in several ways. there have been different recommendations about what people should eat to maintain a healthy diet. For example. obeSiTy An estimated 60% of Americans are overweight and 25% of them are obese. instead of fat. Another method of measuring obesity is to measure percentage of body fat. the recommendations have changed accordingly. As experts have learned more about nutrition and the human body. For many years. This method does not take into account an athlete who may weigh more than a nonathlete because of muscle. One method states that a person who weighs more than 20% over the ideal weight according to the height/weight chart is obese. it does not need them in all the same amounts. the body requires more carbohydrates than fats. In the past.guides to Healthy eating 1 ratio of body weight to height and attempts to adjust for body size. These people probably eat less than normal and still gain weight. Many people have desk jobs instead of doing manual labor. instead of it being a natural part of their lives. More people watch sports instead of participate in them. so has a more sedentary lifestyle. People ride or drive rather than walk. A small number of people are genetically programmed to convert nutrients to fat. Obese = > 30 According to the World Health Organization (WHO). and hypertension has increased around the world. and gallbladder disease. Another group of people cannot control their eating. type 2 diabetes mellitus. sometimes consuming 20. fat has become a principal component of people’s diets. the incidence of diseases such as heart disease. no matter what. There are many reasons why people may become obese. obesity has become a worldwide problem that has significant effects on health. As modern conveniences in the home and workplace have spread. Over many years.000 calories at one meal. Because of obesity. Problems that were once considered limited to developed or industrialized countries now affect everyone. They have an increased risk of breast. humans developed methods of conserving fat to survive possible famines. An even smaller group of people have a very low metabolic rate because of thyroid problems and cannot metabolize nutrients properly. Obese individuals are also prone to pulmonary disease. varicose veins. Overweight = 25–30. Many others have to schedule time to exercise. and colon cancers. The incidence of obesity has increased for a variety of reasons. uterine. Although people . as follows: BMI = Body Weight in Pounds x 705 (Height in Inches)2 Normal = < 25. Some weight reduction programs have helped people lose weight through behavioral modification. The simplest way to prevent being overweight or obese is to eat less and exercise more. A more radical procedure. This band can be tightened or loosened as needed to restrict the size of the stomach. Eating a very low-calorie diet can also help people lose weight. this can lead to dehydration. A third surgical method. meaning more than 100 pounds (45 kg) overweight. and central nervous system complications. These programs usually last about twelve weeks and must be conducted under medical supervision. but nearly all of these drugs have been found to have harmful side effects and should not be taken for weight loss. The weight is immediately regained when the person is rehydrated. A more radical method of weight loss involves surgery. called vertical banded gastroplasty. which involves psychological counseling and exercise to achieve weight loss.2 dIgestIon and nutrItIon have increased their consumption of it. and when other methods have been unsuccessful. makes a small stomach within . potassium loss. called a gastric bypass. This method limits both the amount taken into the stomach and the amount of nutrients that can be absorbed through the small intestine. Several surgical interventions exist. they still have metabolisms that conserve fat whenever possible. This method should only be used when the person is morbidly obese.1). In one procedure. an adjustable gastric band can be placed around the stomach. however. Diets high in fat are valued in developing countries and have replaced local diets that have been in place for centuries. Some people resort to diet suppressant drugs. All of the procedures either limit the amount of food that can be taken into the digestive tract or limit the absorption of nutrients once the food gets into the system. involves stapling part of the stomach to make a smaller pouch and attaching a segment of the small intestine to this pouch (Figure 9. Diuretics provide short-term weight loss through loss of water. the person vomits it back out. which accounts for 90% of people with the condition. but is oriented as a triangular pie chart that is color coded for classifications of food. and thus the glucose cannot be used to produce energy. Actual removal of fat is achieved through liposuction and plastic surgery. Individuals with this condition must take insulin injections. If too much is ingested. These last two methods do not affect future eating. The result is similar to the earlier food pyramid that was proposed in 1992. Most people with type 2 .2b). fooD pyrAMiDS AND DiAbeTeS By the late 1980s. which accounts for 10% of people with the condition. which restricts the amount that can be eaten. The program also emphasizes personal activity. In 2006.guides to Healthy eating 3 the stomach. eating proportionately. oils. the U. moderation. Type 2 diabetes. Department of Agriculture (USDA) published revised recommendations entitled “MyPyramid” (Figure 9. is a disease in which either the amount of insulin produced is inadequate or the insulin receptors on the cells do not work properly. and gradual improvement. vegetables. the result is that too much glucose remains in the bloodstream. is a disease in which the body does not produce any insulin. such as grains. and meats and beans. This program provides consumers with help in establishing their own caloric needs and choices for healthy eating.S. variety in the diet. but remove existing fat. In both cases. In 1992. the federal government released nutritional recommendations in the form of the Food Guide Pyramid (Figure 9. milk. There are two major types of diabetes: type 1 and type 2. Diabetes is a condition in which glucose does not pass normally from the blood into certain body tissues.2a). the increased amount of fat in Americans’ diets was causing an increase in heart attacks and strokes. Sample diets tailored to an individual can be developed through an interactive component. fruits. Type 1 diabetes. although drastic.1 gastric bypass surgery is a radical way to fight obesity by making the stomach smaller. The increased body weight and sedentary lifestyles of many individuals are believed to be significant contributors to the development of type 2 diabetes.4 dIgestIon and nutrItIon figure 9. . it has worked for some people. It is only recommended for individuals who are more than 100 pounds overweight. diabetes are overweight. while many carbohydrates create conditions that ultimately harm the body. the vegetable group. eggs. and nuts group. and all carbohydrates are good. and pasta group. and fats. oils. and the meat. the dairy group.guides to Healthy eating 5 figure 9. these groups include the bread. and sweets are to be used sparingly. some fats may actually improve health. research at the Harvard School of Public Health has revealed that the government recommendations were based on some faulty assumptions. rice. and thus the Harvard researchers developed still another food pyramid (Figure 9. dry beans.2a the original food pyramid created by the united states government urges americans to eat from each of the five basic food groups each day. The Harvard alternative pyramid is called the Healthy Eating Pyramid.2c). fish. This guide takes into account the differences . cereal. In reality. Since the Food Guide Pyramid was first recommended. The original pyramid recommendations were based on the assumption that all fats and carbohydrates are equal: All fats are bad. the recommended numbers of servings are listed with each group. poultry. the fruit group.  dIgestIon and nutrItIon figure 9. the pyramid focuses on the number of times a day the food should be eaten. among types of fats and carbohydrates. . Instead of four tiers. not short-term weight loss. Instead of food being measured in terms of servings.2b “MyPyramid” provides consumers with some general guidelines for healthy eating. The new pyramid focuses on individual foods and is designed for lifelong health. there are seven (daily exercise has been added). 2c a food pyramid designed by researchers at Harvard university suggests that americans need to eat more whole grains. which ultimately results in heart attacks and strokes. or hardening of the arteries. fruits. Fats or oils derived from plants tend to have unsaturated fatty acids that are healthier than animal-derived fats that are high in saturated fatty acids. Fish oils. Saturated and trans fats contribute to the development of arteriosclerosis.guides to Healthy eating  figure 9. however. Unsatu- . and vegetables and less red meat and refined grains. tend to be healthier than beef fats.  dIgestIon and nutrItIon rated fats do not contribute to clogging our arteries. With the exception of oils from the palm plant or from coconuts, which are higher in saturated fats than other plant oils, unsaturated fats are healthier for the body. The original pyramid grouped all animal foods with nuts and dry beans and made no mention of plant oils. The recommendations were an effort to decrease fat intake, which was good, but they also decreased the intake of helpful fats, which was harmful. Carbohydrates create an interesting problem. When complex carbohydrates are broken down and absorbed from the digestive tract, their presence in the blood stimulates the release of insulin from the pancreas. Insulin facilitates the transfer of sugar (glucose) from the carbohydrates into the liver, muscle, and body fat. Once inside these three types of tissues, the sugar is metabolized or stored. If the body has more sugar than is needed for energy, the sugar is stored, mostly as triglycerides (see Chapter 2), a principal component of body fat. The more sugar a person eats, the fatter the DID YOU KNOW? Food prepared with unsaturated fats spoils faster than food prepared with saturated fats, so food manufacturers prefer to use saturated fats in their products. Many consumers are aware of the differences between the two types of fatty acids and prefer to buy products that they feel are healthier. thus, some food manufacturers no longer prepare their products with saturated fats. other companies have produced a modified unsaturated fat called a partially hydrogenated fat in which extra hydrogen atoms have been added to unsaturated fatty acids, converting them to a saturated form, but retaining the original chemical name indicating an unsaturated product. these altered fats can be found in some brands of shortening, margarine, and other products that were once derived from animal products. guides to Healthy eating  person gets. The more glucose the body has in the blood, the higher the levels of insulin released to handle the sugar. If a person eats a meal that gets glucose into the blood rapidly, the person’s blood glucose concentration increases quickly with a corresponding high insulin level. The current theory on the development of type 2 diabetes states that if these spikes of glucose and insulin occur frequently, the liver, muscle, and fat tissues may lose sensitivity to insulin. Thus, the body can no longer eliminate glucose from the blood adequately, resulting in the development of diabetes. Different types of carbohydrates are broken down and absorbed at different rates from the digestive tract. Whole grains break down slowly, while refined grains break down quickly, flooding the blood with glucose. As stated above, the rapid increase in the concentration of glucose in the blood may contribute to the development of diabetes. In addition, it also causes more of the glucose to be converted to fats for storage. This fat storage contributes to obesity if the energy is not used in exercise. The original pyramid did not differentiate between these types of carbohydrates. The average American diet is now fairly close to the federal government recommendations, but with a heavier emphasis on animal products than is recommended. Daily, a person eats about seven servings of bread, cereal, rice, or pasta; about five servings of meat, fish, poultry, eggs, nuts, or dry beans; three servings of vegetables; and three servings of milk, yogurt, cheese, and fruit. Fats and sweets have risen to the top tier. gLyCeMiC iNDex To determine which carbohydrates release glucose quickly and which ones release it slowly, more than 300 foods have been evaluated and put on a scale called the glycemic index . The higher the food is on the scale, the more quickly its glucose enters the bloodstream and the higher the spike of insu- 0 dIgestIon and nutrItIon lin that results. Such insulin spikes increase the probability of developing diabetes and obesity. The lower the food is on index, the more slowly it raises the blood sugar level and the more gradual the increase of insulin. The glycemic index was Table 9.1 glyCemIC Index examples fooD Rice (instant) Corn flakes Cheerios Bagel Saltines Macaroni and cheese Raisins Rye bread Banana Danish pastry Oatmeal cookies Orange juice Pita bread Pound cake Oatmeal cereal Ice cream Rice (parboiled) Macaroni Baked beans Grapes Spaghetti Apple Yogurt Milk Chickpeas gLyCeMiC iNDex 91 83 74 72 72 64 64 64 62 59 55 55 54 54 53 50 47 46 43 43 40 38 38 34 33 2). The chocolate shake contained whole milk.guides to Healthy eating 1 originally created to help patients with diabetes control their blood sugars. onions. salt. potassium sorbate. ketchup. they can cause long-term harm. and chocolate shake filled her up. natural and artificial flavors. and 760 mg of sodium.190 calories for lunch with 33. It is no longer confined to the developed countries. the WHO and the United Nations Food and Agriculture Organization (FAO) released a report stating that the ingestion of large amounts of sugars has become a worldwide problem. mono. water. sucrose. but eaten regularly. The index is useful to anyone wishing to choose among the options of the Healthy Eating Pyramid (Fig 9. . imitation vanilla flavor. nonfat milk solids. and pepper. dextrose. and sodium acid pyrophosphate.and diglycerides. 182 grams of carbohydrates. carrageenan. partially hydrogenated soybean oil. processed cocoa. The chocolate syrup in the shake was made from high fructose corn syrup. cellulose gum. 29 g of protein. The fries were made of potatoes. Amy consumed 1. The number of calories and the amount of fats and carbohydrates in this meal may be acceptable occasionally. cream. the carbohydrates to 64 g. and vanillin. fAST-fooD DiLeMMAS Amy’s lunch at the fast-food restaurant of burger. mustard. she would have consumed a total of 610 calories. 80 g of carbohydrates. If she had substituted a small-size diet soda for the shake. guar gum. She had 75 milligrams of cholesterol. and 990 mg of sodium in the meal (Table 9.2c). 25 mg of cholesterol. fries. but with what? Amy’s hamburger was made of a 100% beef patty along with the bun. Change the medium fries to a small size and the total calories drop to 480. but has spread to the developing countries. Glucose is rated at 100.6% of the fat as saturated fats. In March 2003. corn syrup solids. and the sodium to 680 mg. In all. salt. and vitamin A palmitate. natural beef flavor. “regular” corn syrup. pickles. increase the fruits and vegetables. ShAKe 580 14 g 1g 8g 13 g 50 mg 102 g MeD. No matter what the fad diet. Diseases such as heart disease. lower the amount of sodium (salt) in their diet. there are many fad diets being advertised.5 g 4g 0 mg 45 g SMALL frieS 230 11 g 0g 1.5 g 3.2 dIgestIon and nutrItIon largely due to increased urbanization and modernization of traditional diets. Some recommend eating all protein. and diabetes that were once considered limited to industrial countries have become worldwide epidemics. They promise dramatic weight loss over a short period of time.2 nuTrITIonal faCTs hAMb. Fat Sodium Protein Cholesterol Carbohydrates 250 9g 0. Their recommendations are close to the Healthy Eating Pyramid discussed earlier. and exercise regularly.5 g 3g 0 mg 29 g DieT SoDA 0 0g 0g 0g 20 mg 0g 0 mg 0g 520 mg 220 mg 140 mg 250 mg . stroke. The report recommended that people change their daily eating habits and increase their levels of exercise. and they fre- Table 9. frieS 360 18 g 0g 2. The organizations suggested that people reduce the intake of energy-rich foods that are high in saturated fat and sugar. while others recommend special drinks or pills.5 g 12 g 25 mg 35 g of fasT foods ChoC. fAD DieTS Currently. Calories Total Fat Trans Fat Sat. they recommend eating an extremely low number of calories. unsound weight loss programs tend to have some similar characteristics. usually without medical supervision. These diets also cause the body to increase its production of ketones that will cause the body’s pH to become more acidic and cause significant problems in diabetic individuals. People who use these diets to lose weight almost always gain the weight back because the changes the diets suggest are short-term changes that do not affect the person’s life on a long-term basis. but the weight will return immediately when normal hydration is restored. Any decrease in caloric intake will result in the body losing water during the first several days. but mostly from water loss. This can account for the loss of several pounds. 86% of people with anorexia .guides to Healthy eating 3 quently try to make adherents to the diet depend on certain foods. Before going on any diet. Each type of food is handled separately in the mouth. In addition. It is estimated that as many as 7 million women and 1 million men have the condition. Both of these concepts are false. Several diets suggest a diet high in proteins and fats and low in carbohydrates. If fats are used slowly. many of these diets do not include any exercise regimens. individuals should consult their physicians about their ideal body weight and the best way to achieve that weight. or cancel each other out in the intestine. stomach. Some of these diets suggest food combinations that they claim will either accelerate weight loss. Ketones are produced whenever fats are burned. the body can handle the resulting low ketone levels. According to the National Association of Anorexia and Associated Disorders (ANAD). It affects minorities and people of all socioeconomic levels. usually provided by the program for a fee. and intestine. ANorexiA NervoSA Anorexia nervosa is a disease approaching epidemic propor- tions in the United States. These diets will result in immediate weight loss. share one or a small number of desserts with the whole table. however. there are choices. these also taste great. but they are not healthy. For example. to determine portion sizes. the bread may taste good. If the main course is large. this alternative will be cheaper. a teaspoon of butter is equal to the tip of the thumb. but some of the oil used in cooking is always retained in the food and adds a lot of calories and grams of fat to the meal. use the following criteria: • • • • • • • 3 ounces of meat. but it is high on the glycemic index. do not force yourself to eat it all. avoid eating bread before a meal. is another option. and low in other needed nutrients. or poultry is about the size of a deck of cards. . low in fiber. Bring half of it home for a later meal. for making meals healthier when eating out. it is more difficult to learn about the nutritional content of food when eating in a restaurant. If possible. a cup of fresh fruit equals the size of a baseball. ordering and eating smaller portions is one way of eating healthy. for fries or heavy side dishes. Half a cup of rice is half a tennis ball. substituting lower-calorie foods. avoid fried foods. an ounce of cheese equals 4 dice. one medium potato is equal to the size of a computer mouse. fish. this both halves the cost of the meal and halves the calorie and fat intake. ask about how food is cooked and whether or not the sauce is made from cream. ask for sauces on the side. Consider ordering two appetizers instead of a large main course. and result in lower calories and fats. and then use exactly the amount wanted. Instead of ordering a big dessert. Cream sauces taste good.4 dIgestIon and nutrItIon EATING HEALTHY IN RESTAURANTS although it may be easy to read labels for food cooked at home. such as fruit or vegetables. one cup of vegetables is the size of a fist. People who suffer from anorexia nervosa will be malnourished. the person is always hungry. in fact. have an intense fear of weight gain (even when underweight). Everything must be perfect for that person. especially the way his or her body looks. patients will exhibit early aging. They may have trouble sleeping. including their ability to grow. To be diagnosed with anorexia. heal cuts or bruises.000 per case. they will lose bone mass to the extent that they will have osteoporosis. and display moody behavior. In the face of real starvation. which will affect most of their body functions. have a distorted view of his or her body weight or shape. Experts describe anorexic patients as having low self-esteem and as being depressed. That person may prepare fancy meals for others. the body can never be too thin. About 6% of anorexic patients die. he or she will view the body as overweight when it is obviously not. mostly from heart problems caused by low potassium levels. a person must be below 85% of his or her ideal weight. if female. but fights the impulse to eat. compulsive exercise (the person may actually be a successful athlete). absent or irregular menstruation. Some of the warning signs of the syndrome include: selfinduced starvation in the face of significant weight loss and fear of gaining any weight. and. The person who has anorexia may be described as a perfectionist. and fight infections. and. have missed three successive menstrual periods. Eventually. frequently obsessed with food. . sensitivity to cold (loss of body fat decreases insulation in the body). hair loss or excessive body hair. If they survive and the condition continues. Two-thirds of sufferers say that it lasts up to 10 years. To that person. Outpatient treatment may exceed $100. be chronically fatigued.guides to Healthy eating 5 report that the condition began before they reached age 20. and 10% report onset before 10 years of age. but appear to just pick at the food. reading the nutritional information on food labels is an important way to learn how many calories the food contains and the distribution of fats. • • . good source. more. high. “sugar free” foods cannot have more than 0. as follows: • • • • • “High protein” must have at least 10 g of protein per serving. less. extra lean. light.5 grams of sugar per serving. Food described as being “a good source of calcium” must have at least 100 mg of calcium per serving. the Food and drug administration (Fda) has also defined several health claims that can be used to describe food. reduced. and other substances. low. “reduced calorie” or “fewer calorie” foods must have at least 25% fewer calories per serving than a reference food. the federal government has set strict definitions for 12 terms that are used frequently on food labels. dIgestIon and nutrItIon INFORMED CHOICES ABOUT EATING the first and most important aspect in eating a healthy diet is learning about food. and healthy. “Low fat food” means it contains 3 g or less per serving. fewer. including free. “Light” may mean one-third fewer calories or half the fat of a reference food. lean. carbohydrates. Food with “more iron” means that it has at least 10% more than the minimum daily requirement. or a 50% reduction in sodium. guides to Healthy eating  ConneCtions Healthy eating requires eating certain foods in the correct proportions that the body needs. provide information on how to eat healthy. The incidence of type 2 diabetes. heart attack. and stroke in the United States can be attributed to the higher incidence of obesity and unhealthy eating among Americans. . Dietary guides. such as the Food Pyramid and the Healthy Eating Pyramid. 28 feet (ft) 0.62 mile (mi) 3.2 pounds (lbs) 0.454 kg 28.47 L 29.06 quarts 1 gallon (gal) 1 quart (qt) 1 pint (pt) Milliliter Microliter mL or cc µL 1 mL 0.394 inches (in) 1 mile (mi) 1 foot (ft) 1 inch (in) 1 inch (in) Centimeter cm Millimeter mm 1 mm 0.034 fluid ounce (fl oz) 1 fluid ounce (fl oz) 3.Appendix: Conversion Chart UNIT (METRIC) LENGTH Kilometer Meter km m METRIC 1 km 1m 1 cm TO ENGLISH ENGLISH TO METRIC 1.54 cm 25.000 gram) (one-millionth of a gram) VOLUME Liter L 1L 1.35 g (1/1.94 L 0.4 mm 0.035 ounces (oz) 1 pound (lbs) 1 ounce (oz) 0.785 L 0.039 inches (in) (one-millionth of a meter) Micrometer µm WEIGHT (MASS) Kilogram Gram Milligram Microgram kg g mg µg 1 kg 1g 2.57 mL (one-millionth of a liter) TEMPERATURE °C = 5/9 (°F – 32) °F = 9/5 °C + 32 98 .305 m 2.609 km 0. Acidophilus milk Milk product containing lactase. produced in the salivary glands and the pancreas. Acetyl group A two-carbon molecule made from pyruvic acid or the breakdown of fatty acids. triphosphate. Amylopectin Highly branched form of starch.Glossary Abdominal cavity Anatomical cavity below the diaphragm.  . excess levels of acetyl groups lead to ketone production. Adrenal cortex Outer portion of the adrenal gland that produces assorted steroid hormones. Absorption The process by which nutrients pass through the walls of the digestive tract and into the blood. Aldosterone Adrenal cortical hormone primarily responsible for the Amylases Enzymes responsible for the breakdown of starch. Adipose tissue Fat. Aerobic cellular respiration The pathways of cellular respiration that Albumin Primary blood protein that functions to control osmotic pressure between blood and tissues and as a carrier of ions. Amylose Unbranched form of starch. Adventitia Connective tissue covering of the digestive tube. also known as serosa. drugs. Adenosine diphosphate (ADp) Precursor molecule to adenosine Adenosine triphosphate (ATp) Molecule that provides energy used by cells to perform metabolic processes. functions as energy storage and insulation to retain body heat. Anabolism Synthesis of complex biochemicals in the body from simpler ones. mostly triglycerides. the digestive enzyme needed to break apart the sugar lactose found in milk. reabsorption of sodium in the kidneys. require oxygen. and assorted chemicals. buccinator Skeletal muscle used in chewing. If a portion of the plaque breaks off and moves through the vessel. Anorexia nervosa Syndrome resulting in severe weight loss. sites of exchange of materials between the vessels and surrounding tissues. . Capillaries Smallest vessels of the circulatory and lymphatic sys- tems. stored in the gallbladder. secreted bolus Rounded mass of food and saliva that is swallowed. damaging the surrounding tissue. brunner’s glands Glands found in the submucosa of the duodenum. Appendicitis Inflammation of the appendix. found in bile. Anal canal Short section of the large intestine that ends at the anus. Anemia Inability of the blood to deliver an adequate amount of oxygen to body tissues. Appendix Structure attached to the cecum of the large intestine. over a specific period of time. Calculus Another name for tartar. and secreted into the small intestine. Atherosclerosis Development of fatty plaque deposits in the blood vessels. The plaque collects in the lumen of the vessel. it increases the water solubility of digestive fats to facilitate absorption. it may clog the vessel. primarily arteries. basic metabolic rate (bMr) Rate at which the body expends energy bile Substance produced by the liver.100 dIgestIon and nutrItIon Anaerobic cellular respiration The pathways of cellular respiration that do not require oxygen. Calorie The unit of energy needed to raise the temperature of one gram of water by one degree Celsius. Antibodies Proteins produced by lymphocytes (white blood cells) that attack microorganisms and other foreign cells. a state of starvation with associated tissue degeneration and damage. bile salts Salts derived from cholesterol. the solubility of digestive fats. in bile. they increase bilirubin Breakdown product of the heme in hemoglobin. restricting blood flow through the vessel. Columnar epithelial cell Type of cell found lining the respiratory and Connective tissue Type of primary tissue containing cells. digestive tracts. Cholecystokinin (CCK) Hormone made in the duodenum that stimu- lates gallbladder contractions and pancreatic secretions. Chymotrypsin One of the pancreatic enzymes that break down proteins. Colon Longest part of the large intestine. fiber in the diet. fibers. Cellulose Polysaccharide that is not digestible. Carboxypeptidase One of several pancreatic enzymes that break down proteins. Cecum Pouch of tissue at the juncture of the small and large intestines. the digestive tract to body tissues. Colorectal cancer Cancer of the colon or rectum. excess cholesterol is related to increased risk of heart disease. Catabolism Breakdown of complex biochemicals in the body. a precursor of pepsin that assists in protein breakdown. they are ultimately removed from the blood by the liver. Chief cell A cell that makes pepsinogen. and an intracellular matrix. found in the lining of the stomach. are broken down to obtain energy for metabolism. where it increases flexibility. Cholesterol Lipid used to make steroidal hormones and found in cell membranes. Colostomy Removal of part of the colon and attachment of the end of the large intestine to a hole made in the abdominal wall. mainly glucose. Cellular respiration The process by which nutrients.glossary Carbohydrate General term for sugar or starch or similar 101 compound. Chylomicrons Combinations of proteins and lipids that travel from Chyme Material that leaves the stomach and enters the intestines. Cementum Chemical that holds teeth in place. Collagen Protein substance that gives strength to tissues. . Disaccharide Sugar made up of two monosaccharide molecules joined together. enzymes Proteins that increase the rate of chemical reactions.. and bicarbonate. using the energy contained in electrons. and maltose. contraction of the diaphragm causes the lungs to fill with air. chloride. e.g. including sodium. Crown The upper part of a tooth. a common sugar. energy is needed to make or break this type of bond. the part that is visible above the Defecation Process of elimination of feces. elastase A pancreatic enzyme that helps break down proteins. that help regulate the body’s metabolic processes. gums. Diuretics Chemicals that cause increased urination. electrolytes Substances. DNA (Deoxyribonucleic acid) Nucleic acid that contains the heredity information. type 2 involves a decrease in the sensitivity of the cells to insulin. sucrose. enamel Hard material that coats the outside of teeth. Dehydration Loss of water from the body resulting in increasing density of cell cytoplasm and compromised cellular functions. lactose. . potassium. frequently from bacteDermatitis Inflammation of the skin. rial metabolism. type 1 involves deficiencies in insulin production. Dental plaque Buildup of material on teeth. electron transport chain Series of oxidation and reduction reactions that result in the production of ATP. Dextrose Synonym for glucose. Diaphragm Skeletal muscle that divides the thorax from the abdo- men. Digestion The physical and chemical breakdown of food into nutri- ents that can be absorbed by the cells of the body. Diabetes mellitus Disease involving the clearance and proper metabolism of glucose.102 dIgestIon and nutrItIon Covalent bond Strong chemical bond based on the sharing of elec- trons around atoms in the bond. Duodenum First section of the small intestine. glucose levels. estrogen Reproductive hormone. fat Any organic chemical with no surface charges. fats are insoluble in water. usually from amino acids. fundus The part of the stomach below the connection to the gallbladder Organ that stores bile. covers the opening to the trachea dur- 103 ing swallowing. glycolysis Reaction pathway beginning the breakdown of glucose. essential fatty acids Fatty acids that must be included in the diet because humans cannot make them. part of triglycerides. glucagon Hormone produced by the pancreas that increases blood gluconeogenesis Making glucose from other biochemicals. usually concen- trating on one nutrient. epithelium Tissue that covers or lines body organs or structures. resembles starch from plants. glycogen Energy-compound storage found in animals. glycemic index Calculation giving an estimate of the amount that a food will increase blood glucose levels. stimulates the production of other stomach digestive juices. opposes the actions of insulin. and less of those that appear on the top. part of triglycerides. produces secondary sex charac- teristics in females.glossary epiglottis Part of the larynx. esophagus and above the body. also referred to as lipids. . gastrin Hormone secreted by the stomach lining. food pyramid Method of organizing the diet to emphasize greater intake of certain materials that appear at the bottom. fatty acid Chain of carbon atoms with hydrogen atoms attached. essential amino acids Eight amino acids that must be included in the diet because the body cannot synthesize them. may be in single or multiple layers. such as hydrochloric acid and pepsinogen. glycerol Three-carbon compound. may be saturated or unsaturated. fad diets Diets promising significant weight loss. does not require oxygen. high-density lipoprotein (hDL) Combination of proteins and choles- terol frequently called “good cholesterol”. inflammation Normal body reaction to cell damage.104 dIgestIon and nutrItIon goblet cells Mucus-producing cells found in the respiratory and digestive systems. . ionic bond Chemical bond formed by the attraction of positive and Jejunum Middle portion of the small intestine. hydrogen ion Hydrogen atom that is missing an electron and has a positive charge. hormones Chemicals released from glands in the body that control tissue and organ functions. hydrogen bond Chemical bond based on the unequal sharing of electrons. insulin Hormone that decreases the level of blood glucose and increases the storage of energy for the body. heart attack Blockage of a coronary artery resulting in damage to heart tissue and the compromise of cardiac function. negative ions. hemoglobin Chemical that carries oxygen in red blood cells. Keratin Protein that fills the skin cells and helps make the skin waterproof. ileum Last portion of the small intestine. scavenges cholesterol from tissues and returns it to the liver for elimination in bile. usually from the attack of a microorganism. causing damage to the lining of the throat. heartburn Regurgitation of stomach contents. resulting in weak positive and negative charges on the surface of a compound. into the esophagus. including hydrochlo- ric acid. ingestion The process of taking food into the body. growth hormone Pituitary hormone that regulates body growth up to puberty and contributes to carbohydrate metabolism throughout life. needed for the absorption of vitamin B12. intrinsic factor Substance produced by the parietal cells of the stom- ach lining. hemorrhoids Swelling of blood vessels around the anus. it transports triglycerides to tissues and organs. The Krebs cycle accepts acetyl groups and cycles them through a series of reactions. processes carbohydrates. they drain excess fluid from tissues and receive fat-soluble material from digestive tube epithelia. Lymph nodules Concentrations of lymphocytes found in tissues. needed to break down lactose. Lingual lipase Form of lipase made in the salivary glands of the mouth. system. nutritional deficiencies. and acetone. produces antibodies. Lymphatic capillaries Blind-ended. makes blood proteins and clotting factors. leads to . Liver Major organ of the abdomen. Lipids Another term for fats. Loose connective tissue Form of connective tissue found around blood vessels. cholesterol. beta-hydroxybutyric acid. Lamina propria Layer of the mucosa. Krebs cycle One of the pathways in aerobic respiration. the inner portion of the wall of the digestive tube. helps break down dietary triglycerides.” made of proteins. breaking the acetyl group to CO2 and water. the body’s “chemical factory”.glossary Ketones Acidic chemicals produced when excess acetyl groups. results in intestinal cramping and diarrhea. are present. Malabsorption Inability to absorb nutrients adequately. Increased levels of LDLs are associated with increased risk of heart attack and stroke. Low-density lipoprotein (LDL) “Bad cholesterol. 105 such as acetoacedic acid. and triglycerides. and detoxifies drugs and poisons. is not produced in adequate amounts. Highenergy electrons are stripped of intermediate chemicals for ATP production in the electron transport chain. they help screen for foreign material to protect the body from microorganisms. Lactose intolerance Condition in which the enzyme lactase. Laryngopharynx Part of the larynx extending from the back of the mouth to the larynx. smallest vessels of the lymphatic Lymphocyte Type of white blood cell that is involved in the immune response. access genetic information. part of the Nasopharynx Portion of the pharynx found at the back of the nasal passage. e. phosphate. sodium. glucose. contains a nitrog- enous base. galactose are monosaccharides. expressed as nitrogen content. obese Grossly overweight. oropharynx Portion of the pharynx found at the back of the mouth. Monosaccharide Simple sugar molecule. Minerals Metallic elements needed by the body. mucosa. and Mucosa Innermost layer of the wall of the digestive tube. Metabolism Sum of the anabolic and catabolic biochemical path- ways in the body. osteoporosis Abnormal process resulting in a decrease of bone density. . Micelles Mixture of lipids and bile salts that are absorbed from the small intestine into the epithelial cells. and iron. and a sugar. Nucleic acid Form of a biochemical that the body uses to store and Nucleotide Basic building block of nucleic acids.10 dIgestIon and nutrItIon Masseter muscle Muscle found in the cheek and used in chewing. mag- nesium. Microvilli Projections of the membranes of digestive epithelia that increase surface area in the small intestine. potassium. calcium.g. limits may be set by different criteria. Nitrogen balance Determination of an adequate amount of amino acids to support body growth and development. made of smooth muscle. fructose.. Muscularis Third layer of the wall of the digestive tube. Muscularis mucosa Thin layer of smooth muscle. orbicularis oris Skeletal muscle that makes up the lips. osmotic pressure Balance of dissolved material on both sides of a membrane that controls the passage of water between cells and their surrounding tissues. periodontal ligament Ligament that connects a tooth to the jaw. 7. pernicious anemia Deficiency of intrinsic factor. made in the stomach by chief cells. peptide Short chain of amino acids. parietal cells Cells found in the stomach epithelia that produce hydrochloric acid and intrinsic factor. peritonitis Inflammation of the peritoneum. pepsinogen Precursor to pepsin. peristalsis Waves of contractions of smooth muscles that move material through the digestive tube. serve as an anatomical marking for the ileum. similar to saturated fats.9 is acidic. and laryngopharynx. some of which contain taste buds. added. has phospholipids Mixture of phosphates and fatty acids that make up phytosterol Type of plant lipid analogous to cholesterol. peyer’s patches Lymphoid tissue.1 to 14 is alkaline. . begins the diges- tion of proteins. resulting in vitamin B12 deficiency. partially hydrogenated fat Fatty acids that have had hydrogens pepsin Digestive enzyme made from pepsinogen. A pH of 1 to 6. cannot be absorbed by animals.glossary oxidative phosphorylation Process used by the electron transport 10 system to generate ATP from the energy in electrons derived from the Krebs cycle. and 7 is neutral. oro-. ph Scale from 1 to 14 measuring the degree of acidity or alkalinity. pancreas Organ that produces hormones related to glucose metabo- lism (insulin and glucagon) and digestive chemicals. three parts: naso-. most of cell membranes. papillae Structures on the top surface of the tongue. pancreatic lipase Pancreatic enzyme that breaks down triglycerides. which is the membrane that covers the organs in the abdominal cavity. pharynx The passage between the mouth and the esophagus. Small intestine Site where digestion is completed and nutrients are absorbed into the blood and lymph. may be in a single layer or Staphylococcus Infectious bacteria. part food residue. glycogen. proteins Complex molecules made of linked amino acids. pulp Part of the tooth located at the center of the crown. frequent cause of food poisoning. Serosa Connective tissue covering of the digestive tube. rugae Folds of the lining of the stomach that allow for expansion. it closes off Squamous epithelial cell Flat cell. Salivary glands Paired glands around the mouth that produce mucoid or watery saliva. as adventitia. Smooth muscle Type of muscle not under voluntary control. pyruvic acid End product of glycolysis. such as starch. Saturated fat Form of fatty acids that contain the maximum num- ber of hydrogen atoms. stimulates gastric secre- tion and motility and pancreatic secretions. adjacent to the anus. part bacteria. frequent cause of food poisoning.10 dIgestIon and nutrItIon plaque Buildup of material on teeth. and cellulose. contains nerves. when constricted. blood vessels. which is then broken down by the Krebs cycle. . especially with dairy products. Starch Polysaccharide made by plants for energy storage. frequent cause of food poison- ing. makes up a significant part of the digestive tube wall. access to a portion of the digestive tube. Sphincter Circular smooth muscle. Secretin Hormone made in the duodenum. rectum End portion of the intestines. it is converted into lactic acid or to an acetyl group. composed of many glucose units linked together. Salmonella Infectious bacteria. and connective tissue. polysaccharide Multiple monosaccharides linked together. also known Shigella Infectious bacteria. stratified. contains connective tissue. long-term energy storage compound in animals. controls rate of metabolism. Trace metals Minerals that are required by the body in low Trans fats Unsaturated fats that have been partially hydrogenated and made into stiff. concentrations. blood vessels. Substrate phosphorylation Synthesis of ATP using the energy left Tartar White. or yellow-brown deposits on teeth. Tonsils Lymphoid tissue found on the back of the tongue and at the back of the mouth. and nerves. Testosterone Male hormone that stimulates sperm production and is responsible for secondary male sexual characteristics. also known as calculus. works on proteins. Triglyceride Type of lipid consisting of glycerol and three fatty acids. vitamins Chemicals that must be ingested in low concentrations. saturated-like fats. Stretch receptors Specialized neurons that monitor the stretch of the digestive tube. enzymes needed for final digestive steps are found on the villi. Thyroid gland Gland found in the neck. they facilitate enzyme functions. Trypsin Digestive enzyme. . over from a particular chemical reaction. activates other pancreatic enzymes and Unsaturated fat Fatty acid without the maximum number of villi One-millimeter structures found in the small intestine that increase the surface area for absorption. brown. Stroke Rupture of a blood vessel causing bleeding in the cranium and pressure on the brain. hydrogens. Teniae coli Bands of smooth muscle in the large intestine. Submucosa Second layer of the digestive tube wall.glossary Steatorrhea Increased fat in feces. Steroids A type of lipid containing hydrocarbon rings. may be a result of gallbladder 10 problems. under the mucosa. New York: Benjamin Cummings. 2007.. Rev. Human Anatomy & Physiology. Whitney..B. 2005.. org. Available online at http://www. 1993. G. 2008. and S. 6th ed. eds. btinternet. Eating Disorders. C. Tietz Textbook of Clinical Chemistry. Available online at http://www. Johnson. “Health for Life.N. Understanding Nutrition. Human Biology. E. New York: John Wiley & Sons. McDonald’s Nutrition Facts. New York: West Publishing Co. 2008. Tortora.R.com/~johnharker/table3.htm. Rolfes. Saunders Co.com. Ashwood. Philadelphia: W. New York: Benjamin Cummings. Grabowski. ed. Principles of Anatomy and Physiology.R. and S. 2003): 44–72.” Newsweek (January 20. 2nd ed. 2007.mcdonalds.N.J. M.who..Bibliography Burtis. The Glycemic Index—Sample. Marieb. Revised January.R.A...D.anad. Inc. Available online at http://www. and E. E. WHO Expert Report on Diet and Chronic Disease. National Association of Anorexia and Associated Disorders. Available online at http://www.int/mediacentre/releases/2003/ pr20/en/ 110 . Hoboken. Baltimore. S.: John Wiley & Sons. Applications and Case Studies in Clinical Nutrition. N.J.A. 2008.K. Garden City. 2007. Md.Y. Sports Nutrition: Fats and Proteins. Berkeley. Boca Raton. D.: Human Kinetics Publishers. Ritchie. Fla. Fla.J. Daar. N. 2007 Duyff. C.A.. Gastrointestinal System at a Glance. and American Dietetic Association Staff. Calif.J. Di Pasquale. Science.: John Wiley & Sons. ed. Cline. M. 2008. N. LLC. Amino Acids and Proteins for the Athlete: The Anabolic Edge. Kabara. 2007.G. American Dietetic Association Complete Food and Nutrition Guide. N. 111 .J. N. Keshav.L.: John Wiley & Sons. J.: Wiley-Blackwell. Driskell. N.J. Please Don’t Eat the Wallpaper!: The Teenager’s Guide to Avoiding Trans Fats.: CRC Press... 2nd ed. and C.: North Atlantic Books. Fla. 2008. ed.: CRC Press. 2006. N. Dosil.: CRC Press. Dijkstra. Singer. Champaign... Ill.: John Wiley & Sons.J.: Morgan James Publishing. Hoboken. Hoboken. Boca Raton. 2007. 2008. Fatty Acids in Foods and Their Health Implications. J. New York: Simon & Schuster Adult Publishing Group.Further Resources American Dietetic Association. Society and the Supermarket: The Opportunities and Challenges of Nutrigenomics. J. Castle. Hamm. Tsamis. Giroux. C.J. Hamilton. Enriched Wheat and High Fructose Corn Syrup. P. and P. R.: Lippincott Williams & Wilkins. A. Chow. I. 2007.L. Hoboken. 2008.J. Fats Are Good for You: How Saturated Fat and Cholesterol Actually Benefit the Body. Boca Raton. New Family Cookbook for People with Diabetes. Irven. Clark. R. Eating Disorders in Athletes. Hoboken. and W. Trans Fatty Acids. eds. 2006. N.S. Nancy Clark’s Sports Nutrition Guidebook.. 2007. A. Hoboken. T. C.. Ojeda.M..W. Hoboken. Body Structures and Functions. the Movies. 2008. Kitchens. Alameda. and E. Taylor-Butler.S. C. Larsen. McCracken. and L. Mass.: Adams Media Corp. for Special Occasions and More.: John Wiley & Sons. Controlling Cholesterol for Dummies..000 Calorie Bargains in Supermarkets. Warshaw. 2008. Practical Carbohydrate Counting.J. and M.W.: Hunter House. Ky.112 dIgestIon and nutrItIon Maher. and L. San Francisco: Children’s Press. Everything Lactose Free Cookbook: Easy-to-Prepare. Offices. 2007. A. Va. Fong.W. Bolderman. Restaurants. J. 2008. A.. McWilliams. Scott.. Upper Saddle River. Rinzler. Calif. N. Simplified Diet Manual. Food Pyramid. 2008. Mass. Stuart. Alexandria. New York: W.: American Diabetes Association. L... Safe Dieting for Teens. R. 2008. H. 2008. 2008. Going Hungry: 20 Writers on Desire. and Recovering from Anorexia. Weight Loss Surgery with the Adjustable Gastric Band: Everything You Need to Know Before and After Surgery to Lose Weight Successfully. Norton & Co.K.: Da Capo Press. Taylor. Rohrbough.S. Gluten-free Nutrition Guide. The Bloodless Revolution: A Cultural History of Vegetarianism from 1600 to Modern Times. 2008. ed. T. Low-Dairy Alternatives for Your Favorite Meals. New York: Simon & Schuster Adult Publishing Group.: Prentice Hall. Diet Detective’s Calorie Bargain Bible: More than 1. N.A.J. Graf.: John Wiley & Sons. 2008. Avon.: Thompson Delmar Learning. Sewell. M. . Iowa Dietetic Association ed. Thompson. Cambridge. N. K. 2008.J.. New York: Knopf Publishing Group. Platkin. 2008. Self-Denial. C. and K. Florence. 2008. Food Fundamentals. New York: McGrawHill Co. htm Mayo Clinic—Diarrhea www.brainpop.vivo.Further resources 113 Weitzner.org. 2008.colostate.nih.uk Foodborne and Diarrheal Diseases—Centers for Disease Control and Prevention www.digestivedisorders. Atoyac. Ayudando a Personas Con Anorexia. Terapeutas Y Medicos.gov/ncidod/dbmd/foodborne/index.gov/index.digestive.htm National Digestive Diseases Information Clearinghouse www.htm A Voyage Through the Digestive Tract—Colorado State University www.nami. A.niddk. Mexico: Editorial Pax Mexico.org/helpline/anorexia.com/search/?keyword=digestion NAMI: Anorexia Nervosa www.org Digestive Disorders Foundation www.gov/index.com/health/diarrhea/D500292 Movie of Stomach Functions www.htm National Institute of Diabetes and Digestive and Kidney Diseases www.niddk.gastro.nih. Web SiTeS American Gastroenterological Association www. Bulimia Y Comer Compulsivo: Guia Practica Para Maestros.edu/hbooks/pathphys/digestion . Santa Cruz.cdc.mayoclinic. Picture Credits page 14: 21: 26: 28: 33: 35: 39: 42: 44: 48: © Infobase Publishing Visuals Unlimited © Infobase Publishing © Infobase Publishing © Infobase Publishing © Infobase Publishing © Infobase Publishing © Infobase Publishing © Infobase Publishing © Infobase Publishing 53: © Infobase Publishing 55: © Infobase Publishing inset: Visuals Unlimited 60: © Infobase Publishing 63: © Infobase Publishing 69: © Infobase Publishing 84: © Infobase Publishing 85: AP Images 86: © Infobase Publishing 87: © Infobase Publishing 114 . 27 beef. 61. 62 cardiac sphincter. 32–34. 64–65 chyme. 77. 34. See vitamin C aspirin. 40. 36. 68 appendix. 74–75 colostomy. 47. 34. 20. 19 ADP (adenosine diphosphate). 20 amino acids. 20 anorexia nervosa. overview of. 25. 13. 61–62 cholera. 70 colorectal cancer. 73 cholesterol. 79 BMI (body mass index). 26 cecum. 38. defined. 54. 57 aldosterone. 43–44 115 . 34. 82 bicarbonate. 30 carboxypeptidase. 78 bacteria. 40. 58. 64 caffeine. 71 bile salts. 46. 62. 12–13. 59 buccinator muscle. 88–91. 49 aerobic cellular respiration. 62 amylopectin. 71 bismuth salicylate. 68. overview of. 54. 68. 26–27. defined. 30 bilirubin. 72. 38.Index A absorption. 80–81 bolus. 58 blood capillaries. 38. 38. 37. 45 chemical bonds. 58 anus. 76–77. 73 bile. 17 cementum. 49. 70. 20. 26 anaerobic cellular respiration. 94 Brunner’s glands. 67. 22. 17–19. 30–31 chewing. 39. 78 alcohol. 56 chymotrypsin. 59 carbohydrates. 58 atherosclerosis. 87–88 ascorbic acid. 50. sugars carbon dioxide. See also starches. 70–74 basic metabolic rate (BMR). 13. 45–46. 79. 68 cellular respiration. 41 bread. 54. 71 appendicitis. 61. 17 colon. 36. 71 columnar epithelial cells. 27–29 albumin. 31–33. 43 C B B vitamins. 64–65 chylomicrons. 24. 37. 62–64 acetyl groups. 68 arteriosclerosis. 40 amylase. 59 blood clotting. 27 capillaries. 41–49 chief cells. 72 anemia. 13. 34 behavioral modification. 27 anal canal. 17. 54 cholecystokinin (CCK). 72 ATP (adenosine triphosphate). 61. 29–30 adipose tissue. 11. 26–27 adrenal cortex. 93–95 antibiotics. 16 amylose. 62 collagen. 36. 22. 29. 16 anabolism. 52 catabolism. 15–17. 96 calories. 34. 16. 19–22. 52. 70 covalent bonds. 22 adventitia. 30–31 crowns. 24–25. 56–57 calcium. 22 α-linoleic acid. 30 cellulose. 68. 26. 46 dentin. 82 gastric pits. proteins and. 88–89 glutamate. 62 electrolytes. 34 large intestine and. 92–93 digestion. 16 glycolysis. 57. 29. 40. 55–56 globular proteins. 72 dehydration. 15 fundus. 64 amylase and. 34 fad diets and. 89 diaphragm. 50 essential amino acids. 34–40 dimethyl sulfide. 62–64 diuretics. 71. 61 process of digestion and. 74 food pyramids. 30 empty calories. 40. 47 as building blocks. 83. 74–75 defecation reflex. 56–57. 17 enamel. 40 digestive tract and. 39. 43–44. 27 triglycerides and. 19. coli. See also specific enzymes epiglottis. 17. 40. 34. 29 . 61–65 stomach and. 22 exercise. 16 glucose. 82 diets. 37. 74–75. 74. 70 disaccharides. 34–36 esophagus. 37–40 small intestine and. 17. 39. 73 electron transport chain. 31. pancreas and. See also lipids beef and. gallbladder. 19 feces. 78 obesity and. 25 Food Guide Pyramid. 92. 54 E. 18–19 essential fatty acids. 95 E G G cells. 96 malabsorption syndromes and. 62 duodenum. 83–85. 72 fibrous proteins. 49 epithelium. 82 DNA. 49. fad. 49. 65. 17–18 folic acid. 18–19 diet drugs. 34. 32 liver. 11 digestive tract building blocks of. 55–56 galactose. 19–20 vitamins and. 52–57 structure of. 15. 30–31 enzymes. 71 oxidative phosphorylation and. defined. 82 dental hygiene.11 dIgestIon and nutrItIon D defecation. 45 glycemic index. 92–93 fast food. 93 healthy eating and. 15. 46 energy. 78 gastric bands. 91–92 fats. 82 gastric bypass surgery. 72–74 diet. 15 gallbladder. 18 glucagon. 68 dextrose. 12–13. 72. 85 food poisoning. 29. 40 hamburger and. 83–84. 61. 94 glycerol. 54 gastrin. 20 estrogens. See also defecation fiber. 89–91. 61 gluconeogenesis. 45 descending colon. 57–59. 61 F fad diets. 10. 91 diabetes. 71–72. 70. 47. 87–88. 83–89 fructose. 47. 73 elastase. 32–34. 64 glycogen. 23 fatty acids absorption of. 81–82 overview of. 82. 26. 50 diarrhea. 16. 59 lymphocytes. 32–34. 34-37. 47–48. 78 lipids. overview of. 36 lymphatic capillaries. 72 insulin. 54–55. 15. 58. 47 night blindness. 67–75 laryngopharynx. 58 hemoglobin. 50 Helicobacter pylori. 58 nucleases. 43 ketones. 12 iron. 36. 59. 78 loose connective tissue. 36 low-calorie foods. 38. 38. 38. 52 linoleic acid. 67. 18 nasopharynx. overview of. 54 ionic bonds. 54. 16. 59. See also fats liver. 25 hemorrhoids. 62 nucleotides. 70 muscularis mucosa. 34–37. 34. 36. 70 mucus. 12–13 I ileocecal valve. 49 LDL (low-density lipoprotein). 18–19 normal flora. 55–56 hydrochloric acid. 96 malabsorption syndromes. 70 goiter. 15 masseter muscle. 15–17 . keratin and. 61. 78 nitrogen balance. 85–88.Index goblet cells. 87–88 heartburn. 24. 40. 38. 70–71 NSAIDs (nonsteroidal anti-inflammatory drugs). 20–21 Healthy Eating Pyramid. See also lactose intolerance minerals. 62. 40. 62–64 nutrients carbohydrates as. 61 muscularis. 64–65. 88–89 intestinal fluid. 92 heart attacks. 76–77 lamina propria. 40 M J jejunum. 38. 76–77 lactose intolerance. 49. 40 mouth. 59 N K keratin. 65. 54. 20–21 light foods. 22. 76–77. 58. 43 haustra. 72 hormones. 46 metabolism. 41–43 MSG (monosodium glutamate). 36. 47 larynx. 77–79 maltose. 62. 20. 25. 15. 36 nails. 45 mucosa. 78. 73 hydrogen bonds. 78 milk. 57. 45–46 11 H hair. 70 HDL (high-density lipoprotein). 47. 61 intrinsic factor. 17–18. 18 hard palate. 61. 40. overview of. 31. 17. 96 lymph nodules. 57–59. 10. 40. 25 growth hormone. 37–39 insoluble fiber. 70 micelles. 25 monosaccharides. 18 gums. 64. 91. 20 lipase. 19–20. 56. 96 lingual lipase. 13. 22. 29–30 L lactase. 47–48. 46 large intestine. 93 Krebs cycle. 57 ingestion. 40. 68 ileum. 25–31 methane. 76 jugular vein. 34. 56 parotid salivary gland. 47 osmotic diarrhea. 17–19 reasons for need for. 31 portion size. 41. 45 rugae. 94 potassium. 46–47 partially hydrogenated fat. 73 osmotic pressure. 21–22 nutritional status. 45 parietal cells. 22 plaque. 30 phytosterol. See vitamin A RNA. 20–21. 88–89 pepsinogen. 40. 19 phosphorylation. 73. 40. 27–28. 61. 57 pyruvic acid. 62 fad diets and. 43. 20 pancreas. healthy eating and. 56 peptides. 73 peritonitis. 27 oxygen. 34. 73 proteins building blocks of. 46–47 salivary glands. 27–29. 13 phospholipids. 87–88 oleic acid. 62 serosa. 62 pancreatic lipase. 54. 38. 20 rapeseed oil. 54–55. 78 osteoporosis. 23–25. 74 saturated fats. 19–20. 34. See α-linoleic acid omega-6 fatty acid. 68 small intestine. 72 . 50. 59 pH. 58 pernicious anemia. 62 papillae. 57–59. 93 pharynx. 34. lipids as. 49 Shigella. 27 pulp. 73 soft palate. 20 omega-3 fatty acid. 87–88 secretin. 61. 41–42 oropharynx. 54–55 protons. 31 diet and. 47–48 phosphates. 46–47 Salmonella bacteria. 62–64 periodontal disease. 19. 45 pyloric sphincter. 46 peristalsis. 54 S safflower oil. 94 retinol. 40 chemical bonds and. 46 polysaccharides. 96 lipid solubility and. 17–18 pepsin and. 25. 43 palmitic acid. 95 oxidative phosphorylation. 96 respiration. 22 overview of. 29–30 O obesity. 20–21 as major nutrients. 54 Peyer’s patches. See linoleic acid orbicularis oris. 37. 80–83 oils. 18–19 plaque (dental). 20 saliva. 68 reduced calorie foods. 38. 37. 45. 15–17. 36-37 sodium. 49 solubility. 18–19 digestive process and. 47. 73 sigmoid colon. 20 rectum. 70 smooth muscle. determination of. 13–14 proteins as. 62 roots. 92–93 healthy eating and. 32 fats. 50. 61–65. 29 R P palate. 38–40 digestive tract and. 12–13 trans fats and. 26–27. 37-38.11 dIgestIon and nutrItIon digestive process and. 30 restaurants. 19–20 overview of. 45–46. 24. 67. 78 stercobilin. 20 vertical banded gastroplasty. 27 trans fats and. 49 squamous epithelial cells. 12–13 large intestine and. 19. 50 teniae coli. 78 overview of. 43 V T tartar. 87–88 subclavian vein. 49–51 carbohydrates and. 82–83 Streptococcus bacteria. 62–63 vitamin A. 15–16. 57 . 68 triglycerides absorption of. 36. 59 sublingual salivary gland. 40. 67. 22 stomach. 21–22 transverse colon. 26–27. 13. 19–20. 79 vitamins. 70 uvula. 20. 78–79. 78 vitamin C. 26 sucrose. 47 building blocks of. 34-36. 43. 47 Staphylococcus bacteria. 23–25. 56 strokes. obesity and. 23–24. 78–79 vitamin E. defined. 49 tonsils. 52–57. 87–88 urinary tract infections. 24. See also specific vitamins W water absorption of. 38. 88–89 chemical bonds and. 40 LDL and. 67 stomach and. 73–74 digestive process and. 46–47 submucosa. 91–92. 46 taste buds. 56. 73. 21–22 trypsin. 24–25 vitamin D. 39–40 diuretics and. 52 malabsorption syndromes and. 81 tongue. 45 teeth. 82–83 swallowing. 65 diarrhea and. 45–46 stretch receptors. 47. 46–47 submandibular salivary gland. 71 steroids. 58 unsaturated fats. 41. 45 sphincters. 93 hydrogen bonds and. 43–45. 25 trans fats. 30 substrates. 96 surgery. 52 stearic acid. 17. 64–65 amylase and. 25. 20 lingual lipase and. 70 testosterone. 15 sugars. 79 vitamin K. 43. 40 vegetable oils. 19 oxidative phosphorylation and. 46. 59. 22 thyroid. 82–83 villi. 22. 38. 31 digestive tract and. 82 fad diets and. 59 substrate phosphorylation. 45–46 trace metals. 20 steatorrhea. 40. 16. 62 11 U ulcers. 34. 74 starches.Index speech. Sullivan teaches in both the medical laboratory science and the biology curriculums.About the Author Robert Sullivan. the use of medical laboratory assays to evaluate the nutritional status of athletes. and international issues in laboratory medicine. is an associate professor of medical laboratory sciences at Marist College in Poughkeepsie. His research interests include the toxic effects of heavy metals in alternative medicines. MT (ASCP). Dr. 120 .. New York.D. Ph.