1CHEMICAL COORDINATION IN ANIMALS y y y Endocrinology is the study of endocrine glands, hormones and their effect. Father of endocrinology ² Thomas Addison. Endocrine gland is an isolated gland that pours its secretion directly into venous blood or lymph for passage to different organs in order to control their growth, function, metabolism etc. Endocrine gland is also called as ductless gland. Heterocrine gland (mixed gland) consists of both exocrine and endocrine regions. Exocrine part releases secretion in duct, while endocrine part release hormones in blood. e.g. pancreas and gonads. Hormones are chemical substances which are required in minute quantity for functioning of the body. Hormones are biogenic in origin. Secretin was the first hormone discovered by Bayliss and Starling. Hormones may be excitatory or inhibitory in their effects. On the basis of their chemical composition, hormones may be divided into three categories ² amine hormones, steroids and proteinaceous and peptide hormones. Amine hormones are derived from tyrosine and have an amino group. e.g. thyroxine, epinephrine, norepinephrine, dopamine etc. Steroids are fat soluble hormones and have sterol group. These are derived from cholesterol. e.g. hormones of adrenal cortex, testes and ovaries. Proteinaceous and peptide hormone are water soluble and include hormones of hypothalamus, pancreas and pituitary. Receptor on target cell is located either on the surface of the plasma membrane or in the cell, depending upon the hormone. Hormones which control activity of other endocrine glands or growth are called trophic hormones. Pineal gland is a stalked, small rounded gland found behind the anterior choroid plexus on the epithalamus. It secretes two biogenic amine hormones serotonin and melatonin. Melatonin is synthesized from serotonin derived from tryptophan. Melatonin delays sexual development and inhibits ovarian functions, hence referred as antigonadotrophic hormone. Brain sands (also called acervuli), found in pineal body, are particles of calcium salts (CaCO3 & Ca3PO4). Hypothalamus is the floor of diencephalon. It is formed of masses of gray matter, called hypothalamic nuclei, containing neurosecretory cells. y y y y y y y y y y y y y y y y y y y y Growth inhibiting hormone (GIH) or somatostatin inhibits adenohypophysis to secrete growth-hormone. Hypogonadism in male is caused by genetic inability of the hypothalamus to secrete gonadotropin releasing hormone. Thyrotropin releasing hormone (TRH) stimulates anterior pituitary to secrete thyrotropin or thyroid stimulating hormone. Prolactin inhibiting hormone (PIH) stops synthesis of LTH by anterior pituitary. Adrenocorticotropin releasing hormone (ACTH-RH) stimulates anterior pituitary to secrete adrenocorticotropin or adrenocorticotrophic hormone. This is known as adiposogenital syndrome or hypothalamic eunuchoidism. Prolactin releasing hormone (PRH) stimulates anterior pituitary to secrete prolactin or LTH. (MSH-RH) induces Melanocyte stimulating hormone inhibiting hormone (MSH-IH) stops synthesis of MSH. . It regulates most of the physiological activities of body and maintains homeostasis inside the body. Melanocyte stimulating hormone releasing hormone intermediate lobe of pituitary to secrete MSH. a hypothalamic hormone called gonadotrophin releasing hormone (GnRH) stimulates the pituitary to release gonadotrophins like FSH and LH. both passing through the pituitary stalk or infundibulum. These neurohormones are carried by hypophyseal portal system to adenohypophysis (anterior pituitary) and these stimulate or inhibit the release of trophic hormones from adenohypophysis.2 y Hormones produced by hypothalamus are of two types. For e. These hormones reach anterior pituitary via hypophyseal portal vein and regulate its functions. It is connected with anterior pituitary lobe by blood capillaries of hypophyseal portal system and with the posterior pituitary lobe by axons of its neurons. which are of two types FSH & LH. Gonadotropin releasing hormone (GnRH) stimulates secretion gonadotropins by adenohypophysis. of y y y y y y y y y y y y y y y y y y Somatotropin releasing hormone or growth hormone releasing hormone (SRH or GH-RH) stimulates production of growth hormone by anterior pituitary. The posterior pituitary is under the direct neural regulation of the hypothalamus. The hypothalamic hormones arise in its neurons and pass through axons and are released from their nerve endings.g. the releasing hormones which stimulate the secretion of pituitary hormones and inhibiting hormones which inhibit the secretion of pituitary hormones. Neurosecretory cells secrete neurohormones called releasing factor (RF) or inhibiting factors (IF). Hormones of anterior pituitary are called trophic hormones or tropins. It lies in the cavity called sella tursica of sphenoid bone of skull. Pars distalis and pars intermedia are collectively known as adenohypophysis. caused by deficiency of STH in children is characterised by retarded physical growth but they have normal brain. It is formed of three parts . Hyposecretion leads to thyroid atrophy while hyperactivity produces symptoms similar to Grave·s disease. a proteinaceous hormone is secreted by pars distalis. It is characterised by extra ordinary growth in height due to abnormal elongation of long bones in childhood before the fusion of epiphysis. These are also called pituitary giants. It is also called as hypophysis. Dwarfism. It stimulates growth of body by synthesis and deposition of protein in tissue. Pituitary is a composite gland comprising of anterior lobe (adenohypophysis) and posterior lobe (neurohypophysis). y y y y y y y y y y y y Simmond·s disease occurs due to hyposecretion as a result of damage to pituitary. pea shaped endocrine gland which is connected to hypothalamus by an infundibular stalk formed of connective tissue with blood capillaries and nerves. ACTH is a peptide hormone which controls the structure and functioning of adrenal cortex especially secretion of glucocorticoids and sex corticoids. . increased glucose level in blood by decreased secretion of insulin. It controls structure and functioning of thyroid including synthesis and release of hormones. Adenohypophysis develops as an outgrowth of pharynx called Rathke·s pouch. pars nervosa and pars intermedia.pars distalis. These dwarfs are called midgets. Hormones of adenohypophysis are: TSH. GH (or STH) is a proteinaceous hormone.3 y Pituitary is the smallest. Over secretion of STH results in gigantism in children. increased cell division and increased growth of bones by increased absorption of calcium from intestine. Secretion of the trophic hormones is controlled by neurohormones of hypothalamus through a feedback mechanism which operates either at gene level or at enzyme level.The pars distalis is called anterior pituitary. It is non functional in man. FSH or follicle stimulating hormone is also called gametokinetic factor It is a proteinaceous hormone which stimulates spematogenesis in testes. LH stimulates ovulation. LH (Luteinizing hormone) is known as gamete releasing factor. characterised by abnormal elongation of limbs & lower jaw. It influences the water balance by reducing output of urine. It is also called milk ejection hormone because it stimulates ejection of milk secreted by mammary glands under control of PRL or LTH. y y y y y y y y y y y y y y y y y y y y y y . Its secretion is stimulated by rise in osmotic pressure of blood due to loss of water. This hormone is essential for reabsorption of water in kidney tubules particularly in DCT (distal convoluted tubules). development of corpus luteum and secretion of progesterone in females. Neurohypophysis develops as a downgrowth of hypothalamus and forms pars nervosa. Gonadotropins or gonadotrophic hormone (GTH) regulates the growth and function of gonads. secrete two octapeptide hormones oxytocin and vasopressin. giving gorilla like appearance and protruding bony ridges over the eyes. MSH (also called intermedin). polydipsia and dehydration. Oxytocin (pitocin) is also called birth hormone because it stimulates uterine contraction during child birth. ICSH (Interstitial Cell Stimulating Hormone) activates interstitial or Leydig cells of testes to secrete testosterone and other androgens for the development of secondary sex organs & secondary sexual characters. PRL is also known as hormone of maternity. maturation of Graafian follicle and secretion of estrogen in ovaries. Vasopressin is also called antidiuretic hormone (ADH) or pitressin. It stimulates synthesis and dispersal of melanin pigment present in skin of fish. a polypeptide hormone is produced by pars intermedia.4 y Over secretion of STH in adults results in acromegaly. Deficiency of ADH causes diabetes insipidus characterised by diuresis. Pituiticyte cells formed in neurohypophysis. PRL stimulates development of mammary gland during pregnancy and lactation after child birth. amphibia and some reptiles. The two main GTH are FSH and LH/ICSH. It also stimulates secretion of progesterone from corpus luteum. 5 y y y y y y y y y y y y Structures present in pituitary which store neurosecretory substances of hypothalamus are called Herring bodies. TSH or both (iii) an inadequate dietary supply of iodine The symptoms include reduction of overall metabolic activity and poor tolerance of cold. low heart rate and body temperature. thyroxine also controls some developmental processes like metamorphosis. The BMR of a normal adult man and woman is 40 cal/m2 and 37. occurs in adults due to y y y y y y y y It is characterised by puffy appearance due to subcutaneous accumulation of fat. maintains nervous and muscular tone. pigeon chest. retarded mental development.5 cal/m2 respectively. Myxoedema also hyposecretion. amphibia & teleost fish. Thyroid is the largest endocrine gland. decreased body temperature. retarded sexuality etc. Hypothyroidism results in cretinism. increase the oxidation of glucose in tissue and also acts on SA node & maintains the normal heart beat and also reduce the formation of ketone bodies etc. Follicles secrete iodinated triiodothyronine (T3). Thyroxine controls BMR (basal metabolic rate) of the body. prolonged neonatal jaundice. e. Parafollicular cells are groups of endocrine cells scattered in connective tissue and between the thyroid follicle. Subneural gland of Amphioxus is homologous to pituitary of vertebrates. It controls urine output. low BMR. a disease of infants is characterized by decreased BMR. lethargy. delayed puberty. T3 is more active (3 to 4 times) than T4. myxoedema. called Gull·s disease. stunted growth. Hypothyroidism can result from (i) primary failure of thyroid gland itself (ii) hyposecretion of TRH. having two lobes attached by an isthmus at the upper end of trachea below larynx. Other clinical features include dry skin. Cretinism. . respiratory problems and constipation. Apart from carrying out metabolic and regulatory function. amino acids tetraiodothyronine (T4)and Tetraiodothyronine is popularly called thyroxine. It consists of small oval or rounded thyroid follicles held together by connective tissue.g. endemic or simple goitre or colloid goitre and Hashimoto·s disease. Thyroxine (T4) is produced in greater in quantity than T3. Its secretory cells are called as chief cells. Amphioxus etc. PTH maintains calcium level in blood and lowers the serum phosphate. Hashimoto·s disease is also called auto-immune thyroiditis. Exophthalmic goitre is characterised by enlarged thyroid gland. is homologus to thyroid gland. It is soft bilobed mass of lymphoid tissue located in the mediastinum just by the side of the heart. increased BMR.6 y y Simple goitre is characterised by enlarged thyroid gland which brings about a swelling in the neck region. Hypoparathyroidism leads to parathyroid tetany while hyperparathyroidism results in osteitis fibrosa cystica (Formation of fibrous cysts in the bone due to excess of phosphate ions and a consequent decreased bone Ca2+) leading to painful swelling of the bones and weakening (osteoporosis). Grave·s disease is an autoimmune disorder in antibodies that mimic the effect of TSH are produced. It can be corrected by removing a part of the gland. Hyperthyroidism result in Graves· disease which is also called exophthalmic goitre. Simple goitre is called iodine deficiency goitre or endemic goitre because it occurs in northern hilly areas where soil and ground water is deficient of iodine. It secretes single proteinaceous hormone called PTH/ parathyroid hormone/Collip·s hormone. heart rate. Hypocalcemic tetany is characterised by fall in calcium level in blood and causes painful spasmodic contraction of muscles of face. Parathyroid gland consists of solid vascular mass of secretory cells. cardiac output. pulse rate. It inhibits osteoclast cells. usually occurs in middle aged females due to sensitisation of their own thyroid proteins called thyroglobuin. body temperature. Two pairs of parathyroid glands are wholly or partly embedded in the dorsal surface of the thyroid gland. hands. Another non-iodinized parafollicular cells. These are not regulated by the normal negative feedback controls. protrusion of eyes or exophthalmia. feet and increased neuro-excitation. Endostyles of lower chordates like Herdmania. Thymus is temporary gland which is haemopoietic as well as endocrine. y y y y y y y y y y . hormone called calcitonin is secreted by y y y y y y y It is hypocalcemic and hypophosphatemic peptide hormone which checks excess plasma Ca2+ and phosphate by decreasing mobilisation of Ca2+ from bones. Aldosterone is also called as salt-retaining hormone. outer cortex (mesodermal in origin) and inner medulla (ectodermal in origin). Imbalance in sodium potassium ratios alter muscle and nerve functions. development of resistance to infection and attainment of sexual maturity. Important glucocorticoids (secreted by zona fasciculata) are cortisol and corticosterone. Adrenal cortex is further subdivided into 3 main zones: outer zona glomerulosa. Thymopoietin or thymin. tetany. muscular weakness. Cl and HCO3 takes place and level of K+ ion increases in blood. divided into mineralocorticoids. In Addison·s disease. It maintains electrolyte and water balance in body. y y y y . Thymosin. Adrenal gland is also known as supra renal gland as it is located on upper side of each kidney. hypokalemic alkalosis. After sexual maturity thymus regresses and its place is taken up by fatty and fibrous connective tissue. It has many rounded concentric layered structures called Hassall·s corpuscles (also called thymic corpuscles) which act as phagocytes. Its secreteion is stimulated with rise in K+ or fall in Na+ and blood volume. accelerates cell division. Three types of thymus hormones are thymosin. thymin I and thymin II. Conn·s syndrome is characterised by rise in blood volume and blood pressure. glucocorticoids and y y y y y y y y y y y y y y Two common mineralocorticoids (secreted by zona glomerulosa) are aldosterone and deoxycorticosterone. Adrenal gland is divided into two distinct regions. Corticoids are sexcorticoids.7 y y y y It is ectodermal in origin. a polypeptide hormone. lymphocytes formation. Adrenal cortex composed of cortical cells. high plasma Na+ (due to decreased renal excretion) resulting in kidney damage and polyuria. It also stimulates sodium reabsorption by the nephrons in the kidney. excessive loss of Na+. depresses neuromuscular transmission. induces Tcell markers and has role in the generation of cytotoxic T-cells and prevention of autoimmunity. middle zona fasciculata and inner zona reticularis. Hypersecretion of aldosterone due to adrenal cortical tumor causes aldosteronism or Conn·s syndrome. Addison·s disease usually results due to deficient secretion of aldosterone. The most common cause of Addison·s disease is atrophy of the adrenals resulting from tuberculosis. secretes 40 different steroid hormones which are collectively called as corticoids. asthma etc. emotional stress. acts as vasodilator. Secretion of glucocorticoids and sexcorticoids are regulated by ACTH of pituitary. pain anger. Glandular cells of adrenal medula are called chromaffin cells which secretes two hormones-adrenalin or epinephrine and noradrenalin or norepinephrine. high Na+ & low K+ concentration in plasma.8 y y Most important glucocorticoid is cortisol. noradrenalin and dopamine are collectively called catecholamines. which influences carbohydrate metabolism and also effect protein and fat metabolism. Dopamine is an intermediate in the biosynthesis of adrenalin and noradrenalin from the tyrosine and phenylalanine. Adrenalin. loss of sugar in urine. A deficiency of dopamine results in Parkinson·s disease Secretion of adrenalin is 5-10 times higher that noradrenalin. Mineralocorticoid release is stimulated by the activity of renin and angiotensin. These hormones are secreted for meeting an emergency as in cold. beard. increases sugar level in blood by stimulating glycogenolysis in liver and skeletal muscle and slows down peristalsis. skin disease. secreted by zona recticularis and zona fasciculata. includes androstenedione. dehydroepiandrosterone (DHEA) etc. characterised by high sugar level in blood. Adrenal medulla is stimulated by sympathetic system. These are steroid androgen hormones. It also secretes small amount of female sex hormones like estrogen and progesterone. Sex corticoids. fear etc. moustaches in females. Over secretion of cortisol causes Cushing·s syndrome. lipolysis in adipose tissue to increase level of fatty acids in blood. Glucocorticoids are used maximally in medicine for allergic condition. y y y y y y y y y y y y y y y y y y . They stimulate the development of secondary sexual characters of male type. rheumatoid arthritis. Hirsutism is a presence of excess facial and body hair in females due to adrenal virilism. Causes constriction of skin and visceral smooth muscle capillaries. rise in blood volume and blood pressure etc. basal metabolic rate. androsterone. increases respiration rate as it dilates trachea. loss of weight. while it causes gynaecomastia in males characterised by enlarged breasts. Excessive secretion of sex corticoids results in virilism or appearance of male secondary sexual characters like male voice. These hormones are derived from aminoacid tyrosine. Adrenalin increases blood pressure. weight loss in spite of polyphagia (increased appetite). It increases blood sugar level by promoting glycogenolysis in liver cells. y y Hypersecretion of adrenalin causes hypertension.E cell secretes glucagon. glycosuria. fight and fright. Deficiency of adrenalin or noradrenaline does not produce any marked physical deformity being emergency hormones. Pancreas is the second largest gland located in the loop of duodenum.) Diabetes is characterised by polyuria. H cell secretes somatostatin and F cell secretes pancreatic polypeptides. acidosis (increased H+ ions in blood) and coma. These are: . erection of hairs. F cell secretes insulin. It is an heterocrine gland in which exocrine part occurs as acini while the endocrine part (2-3%) is represented by islets of Langerhans or pancreatic islets. exercises lesser effect on cardiac activity and produces greater constriction of blood vessels in muscles. and indirectly causing the liver to take up glucose. Hormones of pancreas are secreted by different types of endocrine cells. (ii) Promoting both oxidation of glucose and conversion of glucose into glycogen in muscles and liver cells. increase in oxygen consumption. Insulin is also called hypoglycaemic or antidiabetic factor. K cell secretes gastrin. Adrenal is also called 4S gland for sugar metabolism. sex hormones and source of energy. polydipsia. Normal range of blood sugar is 80-120 mg/100 ml of blood (80 before fasting and 120 after meal. y y y y y y y y y y y y y y . and stimulating protein synthesis while inhibiting protein breakdown. increase in breakdown of lipids. (iv) promoting synthesis of fats from glucose by adipose tissue and also inhibiting metabolic breakdown of fat (v) promoting uptake of amino acids by liver and muscle cells. Glucagon is a proteinaceous hormone whose secretion is stimulated by low blood sugar level. hyperglycemia. Noradrenalin more or less resembles adrenalin in its biological effects except that it operates during normal state. ketosis (increased ketone bodies in blood). (iii) inhibiting metabolic breakdown of stored glycogen in liver and muscle cells. salt retaining.9 dilation of arterioles of heart and skeletal muscles. Adrenal gland is also called as emergency gland and ¶triple· F gland for flight. It decreases blood sugar level and the formation of ketone bodies and increases lipolysis in blood and liver. dilation of pupils. Insulin lowers blood glucose by (i) stimulating transport of glucose from blood to muscle and adipose cells. Deficiency of insulin causes diabetes mellitus. Secretion of estrogen is stimulated by LH of anterior lobe of pituitary gland. Castrated human male is called eunuch or neuter and oxen (instead of bulls) in case of cattle. to excrete more amount of sugar. Type II diabetes usually develops after the age of 40 and is not associated with total loss of the ability to secrete insulin. androsterone. Type I diabetes is also called juvenile diabetes or insulin-dependent diabetes mellitus (IDDM). The ovaries are cytogenic as well as endocrine in function. y y y y y y y y y y y y y y y y y y y y .) and male secondary characteristics (like beard. Gonads (testes in males and ovary in females) are both exocrine and endocrine in function. which secrete male hormone. Four types of androgen are testosterone. Polyuria or excessive urination is due to increase in water content of urine. Estrogen. rather insulin resistance develops especially in skeletal muscles. Eunuchoidism is hormonal disorder due to non secretion of testosterone in a genetically male individual.10 y Indication of diabetes start when blood sugar level increases about 3 times and is more than 150 mg/100 ml of blood due to regular supply from alimentary canal and failure of cells to absorb glucose. Pancreatic polypeptide checks secretory activity of digestive glands. Estrogen includes estradiol. seminal vesicle etc. Polydipsia means excessive thirst inspite of drinking more water. epiandrosterone and dehydroepiandrosterone (DHEA). Type I diabetes is an auto-immune disorder which usually develops before the age of 40 and it is characterised by loss of F -cells with eventual absence of insulin in the circulation. moustaches etc. a steroid hormone. Endocrine part of testis is formed of group of cells called Interstitial cells or Leydig cells.) It stimulates spermatogenesis and erythropoiesis. Testosterone. estriol and estrone. Diabetes mellitus is of two types-type I diabetes and type II diabetes. Somatostatin is a local hormone which controls functioning of E and F cells. It is ketosis prone diabetes means that fatal high level of ketone bodies increase in the blood due to severe non-availability of insulin. is responsible for the growth and development of male secondary sex organs (like epididymis. It is ketosis-resistant diabetes. group of steroid hormone is mainly secreted by follicular epithelial cells of membrana granulosa of Graafian follicles. androgen. Type II diabetes is also called maturity-onset diabetes or non-insulin dependent diabetes mellitus (NIDDM). estradiol is also secreted by placenta. development of placenta and growth of secretory alveoli in mammary glands. secreted by corpus albicans which is formed from the corpus luteum at the end of gestation period. placenta also acts as an endocrine gland. Progesterone is a steroid hormone secreted by corpus luteum. During pregnancy progesterone helps in attaching embryo to uterine wall. HPL (human placental lactogenic hormone) prepares the mammary glands to secrete milk. hence called as pregnancy hormone. ICSH) of pituitary. Hormones of heart: The atrial walls of the heart secrete a very important peptide hormone. HCG and placental lactogen. Small amount of progesterone is also secreted by adrenal cortex and placenta. Pregnancy test is confirmed by the presence of HCG is urine. this role is played by estrogens and progesterone. It supplements the effect of excess sex hormones for depressing gonadotrophic activity (FSH. During pregnancy. ANF causes vasodilation which decreases BP and increases urinary excretion of Na+. LH. Relaxin is a proteinaceous hormone. During pregnancy. Progesterone is responsible for the maintenance of pregnancy. Atrial natriuretic factor (ANF). placenta and testes. excretion. It softens the pubic symphysis. Hormones of kidney: The juxtaglomerular cells of the kidney produce a peptide hormone called erythropoietin. True placenta is found in eutherians. HCG is a glycoproteinaceous hormone which maintains the corpus luteum for continued secretion of progesterone so as to maintain the pregnancy. PL). y y y y y y y y y . Inhibin hormone is produced by corpus luteum. ANF is secreted in response to increase in blood pressure or increase in Na+ ions in the blood. Progesterone is thermogenic and is probably responsible for the rise in basal body temperature at the time of ovulation. It decreases the secretion of FSH while increases the secretion of LH during menstrual cycle.11 y y y y y y y y y y y y y y Estrogen stimulates the growth and development of female secondary sex organs and female secondary sexual characteristics. The chorionic villi of placenta secretes steroid hormones (estradiol and progesterone) and protein hormones (human chorionic gonadotrophin. nutrition etc. Placenta is the connection between foetus and uterine wall for physiological exchange like respiration. thus helps in parturition (child birth) in rats and guinea pigs. In women. Membrane-bound receptors are present on the cell membrane of target cells.12 y y It stimulates bone marrow cells to form RBCs. T3. On the basis of solubility. The hormone-receptor complex enters the nucleus and binds to specific regulatory sites on the chromosomes. Cholecystokinin (CCK) 4. initiating the transcription of some genes (DNA). Secretin 3. T4 and steroid hormones act in this manner. The binding alters the pattern of gene expression. the hormones are lipid soluble or water soluble. The hormone is said to be the first messenger and after binding with membrane receptor it activates a second. Gastrin 2. . The formation of RBCs is called erythropoiesis. proteins and usually enzymes. Gastric inhibitory peptide (GIP) y y y y y y y y y y y y y y y MECHANISM of HORMONE ACTION Hormones produce their effects on target tissues by binding to specific proteins called hormone receptors located in target tissues only. When the hormone is bound with receptor. Hormone-receptor complex formation leads to certain biochemical changes in the target tissue.messenger in the cytoplasm of the target cell. The second-messenger (b) Inositoltriphosphate (d) cyclic GMP (cGMP) can (IP3) be(a) Cyclic AMP (cAMP) (c) Calcium ions (Ca2+) y y The second messenger in turn regulates cellular metabolism by activating or inactivating certain enzymes. Intracellular receptors are present in the cytoplasm of target cells. a hormone-receptor complex is formed.bound receptors. The actions of lipid soluble hormones are slower and last longer than the actions of water soluble hormones. This results in the production of specific mRNA translation products. thus also called cytosolic receptors. Lipid soluble hormones can easily cross the cell membrane and hence bind with cytosolic receptor. Hormones of gastro-intestinal tract: Different parts of GIT secrete four major peptide hormones namely: 1. Water soluble hormones cannot cross the cell membrane but interact with membrane. while repressing the transcription of others.