The Chapter in One Page

The neural system and the endocrine system JOINTLY coordinate and regulate the physiological functions in the body. Neural coordination on its own is not enough, and the chapter gives three reasons: neural coordination is FAST BUT SHORT-LIVED, the nerve fibres do not innervate all the cells of the body, and cellular functions need to be continuously regulated. So a special kind of coordination and integration has to be provided, and this function is carried out by hormones.

Endocrine glands LACK DUCTS and are hence called DUCTLESS GLANDS, and their secretions are called hormones. The chapter gives two definitions. The classical definition is that a hormone is a chemical produced by endocrine glands, released into the blood and transported to a distantly located target organ. The current definition is that hormones are NON-NUTRIENT CHEMICALS which act as INTERCELLULAR MESSENGERS and are produced in TRACE AMOUNTS, and it was written that way because it covers a number of new molecules in addition to the hormones secreted by the organised endocrine glands. Invertebrates possess very simple endocrine systems with few hormones, while a large number of chemicals act as hormones in vertebrates. The organised endocrine bodies are the PITUITARY, PINEAL, THYROID, ADRENAL, PANCREAS, PARATHYROID, THYMUS and GONADS - testis in males and ovary in females - and in addition the GASTROINTESTINAL TRACT, LIVER, KIDNEY and HEART also produce hormones.

The HYPOTHALAMUS is the basal part of the diencephalon, forebrain, and regulates a wide spectrum of body functions. It contains several groups of neurosecretory cells called NUCLEI which produce hormones, and these hormones regulate the synthesis and secretion of pituitary hormones. They are of two types - RELEASING hormones, which stimulate secretion of pituitary hormones, and INHIBITING hormones, which inhibit secretions of pituitary hormones. Gonadotrophin releasing hormone (GnRH) stimulates the pituitary synthesis and release of gonadotrophins, while SOMATOSTATIN from the hypothalamus INHIBITS the release of growth hormone from the pituitary. These hormones originate in the hypothalamic neurons, pass through axons and are released from their nerve endings, then reach the pituitary through a PORTAL CIRCULATORY SYSTEM and regulate the ANTERIOR pituitary, while the POSTERIOR pituitary is under the DIRECT NEURAL regulation of the hypothalamus.

The PITUITARY GLAND is located in a bony cavity called SELLA TURSICA and is attached to the hypothalamus by a stalk. It is divided anatomically into an ADENOHYPOPHYSIS and a NEUROHYPOPHYSIS. The adenohypophysis has two portions - PARS DISTALIS and PARS INTERMEDIA. The pars distalis, commonly called the ANTERIOR PITUITARY, produces SIX hormones - growth hormone (GH), prolactin (PRL), thyroid stimulating hormone (TSH), adrenocorticotrophic hormone (ACTH), luteinizing hormone (LH) and follicle stimulating hormone (FSH). The pars intermedia secretes only ONE hormone, melanocyte stimulating hormone (MSH), and in human beings the pars intermedia is almost merged with the pars distalis. The neurohypophysis, also known as the pars nervosa or posterior pituitary, STORES AND RELEASES two hormones, OXYTOCIN and VASOPRESSIN, which are actually SYNTHESISED BY THE HYPOTHALAMUS and transported axonally to the neurohypophysis.

Over-secretion of GH gives GIGANTISM and low secretion gives PITUITARY DWARFISM, while excess GH in adults, especially in middle age, gives ACROMEGALY, with severe disfigurement especially of the face, which is hard to diagnose in the early stages and may lead to serious complications and premature death if unchecked. PRL regulates the growth of the mammary glands and the formation of milk in them. TSH stimulates the synthesis and secretion of thyroid hormones from the thyroid gland. ACTH stimulates the synthesis and secretion of the steroid hormones called GLUCOCORTICOIDS from the ADRENAL CORTEX. LH and FSH stimulate gonadal activity and are hence called GONADOTROPHINS - in males LH stimulates the synthesis and secretion of androgens from the testis and FSH along with androgens regulates spermatogenesis, and in females LH induces ovulation of the fully mature follicles (graafian follicles) and maintains the corpus luteum, formed from the remnants of the graafian follicle after ovulation, while FSH stimulates the growth and development of the ovarian follicles. MSH acts on the melanocytes and regulates the pigmentation of the skin. Oxytocin acts on the smooth muscles and stimulates their contraction, giving vigorous contraction of the uterus at the time of child birth and milk ejection from the mammary gland. Vasopressin acts mainly at the kidney and stimulates resorption of water and electrolytes by the DISTAL TUBULES, reducing the loss of water through urine, and is hence called the ANTI-DIURETIC HORMONE (ADH); impaired synthesis or release of ADH gives a diminished ability of the kidney to conserve water, with water loss and dehydration - DIABETES INSIPIDUS.

The PINEAL GLAND is located on the DORSAL SIDE OF THE FOREBRAIN and secretes MELATONIN, which regulates the 24-HOUR (DIURNAL) RHYTHM of the body - the normal rhythms of the sleep-wake cycle and body temperature - and also influences metabolism, pigmentation, the menstrual cycle and our defense capability.

The THYROID GLAND is composed of two lobes located on either side of the trachea, interconnected with a thin flap of connective tissue called the ISTHMUS. It is composed of follicles and stromal tissues, and each thyroid follicle is composed of follicular cells enclosing a cavity. The follicular cells synthesise two hormones - TETRAIODOTHYRONINE or THYROXINE (T4\mathrm{T_4}) and TRIIODOTHYRONINE (T3\mathrm{T_3}) - and IODINE is essential for the normal rate of hormone synthesis in the thyroid. Deficiency of iodine in the diet gives HYPOTHYROIDISM and enlargement of the thyroid gland, commonly called GOITRE. Hypothyroidism during pregnancy causes defective development and maturation of the growing baby, giving STUNTED GROWTH (CRETINISM), MENTAL RETARDATION, LOW INTELLIGENCE QUOTIENT, ABNORMAL SKIN and DEAF-MUTISM, and in adult women hypothyroidism may make the menstrual cycle irregular. Cancer of the thyroid gland or the development of nodules raises the rate of synthesis and secretion to abnormally high levels - HYPERTHYROIDISM - and EXOPHTHALMIC GOITRE, also called Graves' disease, is a form of hyperthyroidism characterised by ENLARGEMENT OF THE THYROID GLAND, PROTRUSION OF THE EYEBALLS, INCREASED BASAL METABOLIC RATE and WEIGHT LOSS. Thyroid hormones regulate the BASAL METABOLIC RATE, support the process of RED BLOOD CELL FORMATION, control the metabolism of CARBOHYDRATES, PROTEINS AND FATS, and influence the maintenance of WATER AND ELECTROLYTE BALANCE. The thyroid also secretes a PROTEIN hormone called THYROCALCITONIN (TCT), which regulates the blood calcium level by DECREASING it.

In human beings FOUR PARATHYROID GLANDS are present on the BACK SIDE OF THE THYROID GLAND, one pair each in the two lobes. They secrete a peptide hormone called PARATHYROID HORMONE (PTH), and its secretion is regulated by the circulating levels of calcium ions. PTH INCREASES the Ca2+\mathrm{Ca^{2+}} levels in the blood - it acts on bones and stimulates bone resorption (dissolution or demineralisation), stimulates reabsorption of Ca2+\mathrm{Ca^{2+}} by the renal tubules and increases Ca2+\mathrm{Ca^{2+}} absorption from the digested food. PTH is a HYPERCALCEMIC hormone, and along with TCT it plays a significant role in calcium balance.

The THYMUS is a lobular structure located between the lungs behind the sternum on the ventral side of the aorta, and it plays a major role in the development of the immune system. It secretes peptide hormones called THYMOSINS, which play a major role in the differentiation of T-LYMPHOCYTES, providing CELL-MEDIATED IMMUNITY, and which also promote the production of antibodies to provide HUMORAL IMMUNITY. The thymus is degenerated in old individuals, so thymosin production falls and the immune responses of old persons become weak.

One pair of ADRENAL GLANDS is present, one above each kidney, and each is composed of two types of tissue - the centrally located ADRENAL MEDULLA and, outside it, the ADRENAL CORTEX. Underproduction of hormones by the adrenal CORTEX alters carbohydrate metabolism, causing acute weakness and fatigue - ADDISON'S DISEASE. The adrenal medulla secretes two hormones - ADRENALINE or EPINEPHRINE and NORADRENALINE or NOREPINEPHRINE - commonly called CATECHOLAMINES, which are rapidly secreted in response to stress of any kind and during emergency situations and are hence called EMERGENCY HORMONES or HORMONES OF FIGHT OR FLIGHT. They increase alertness, pupilary dilation, piloerection and sweating, increase the heart beat, the strength of heart contraction and the rate of respiration, and stimulate the breakdown of glycogen, giving increased blood glucose, as well as the breakdown of lipids and proteins. The adrenal cortex has THREE LAYERS - ZONA RETICULARIS (inner), ZONA FASCICULATA (middle) and ZONA GLOMERULOSA (outer) - and its hormones are called CORTICOIDS. GLUCOCORTICOIDS are involved in carbohydrate metabolism and CORTISOL is the main glucocorticoid; MINERALOCORTICOIDS regulate the balance of water and electrolytes and ALDOSTERONE is the main mineralocorticoid. Glucocorticoids stimulate GLUCONEOGENESIS, LIPOLYSIS and PROTEOLYSIS and INHIBIT cellular uptake and utilisation of amino acids; cortisol maintains the cardio-vascular system and kidney functions, produces anti-inflammatory reactions, suppresses the immune response and stimulates RBC production. Aldosterone acts mainly at the renal tubules and stimulates reabsorption of Na+\mathrm{Na^+} and water and excretion of K+\mathrm{K^+} and phosphate ions, helping maintain electrolytes, body fluid volume, osmotic pressure and blood pressure. Small amounts of ANDROGENIC STEROIDS are also secreted by the adrenal cortex and play a role in the growth of axial hair, pubic hair and facial hair during puberty.

The PANCREAS is a COMPOSITE GLAND acting as both an exocrine and an endocrine gland. The endocrine pancreas consists of the 'Islets of Langerhans' - about 1 to 2 million in a normal human pancreas, representing only 1 to 2 per cent of the pancreatic tissue. There are two main cell types - α\alpha-cells, which secrete GLUCAGON, and β\beta-cells, which secrete INSULIN. Glucagon is a peptide hormone which acts mainly on the liver cells (hepatocytes), stimulates GLYCOGENOLYSIS giving HYPERGLYCEMIA, also stimulates GLUCONEOGENESIS, and reduces cellular glucose uptake and utilisation - it is a HYPERGLYCEMIC hormone. Insulin is a peptide hormone which acts mainly on hepatocytes and adipocytes, enhances cellular glucose uptake and utilisation giving a rapid movement of glucose from blood into those cells and DECREASED BLOOD GLUCOSE (HYPOGLYCEMIA), and also stimulates the conversion of glucose to glycogen (GLYCOGENESIS). Glucose homeostasis is maintained JOINTLY by insulin and glucagon. Prolonged hyperglycemia leads to DIABETES MELLITUS, associated with loss of glucose through urine and the formation of harmful compounds known as KETONE BODIES, and diabetic patients are successfully treated with insulin therapy.

A pair of TESTES is present in the scrotal sac, outside the abdomen, and the testis performs dual functions - a primary sex organ AND an endocrine gland. It is composed of seminiferous tubules and stromal or interstitial tissue, and the LEYDIG CELLS or INTERSTITIAL CELLS, present in the intertubular spaces, produce a group of hormones called ANDROGENS, mainly TESTOSTERONE. Androgens regulate the development, maturation and functions of the male accessory sex organs like the epididymis, vas deferens, seminal vesicles, prostate gland and urethra, stimulate muscular growth, growth of facial and axillary hair, aggressiveness and low pitch of voice, play a major stimulatory role in spermatogenesis, act on the central neural system and influence male sexual behaviour (libido), and produce anabolic effects on protein and carbohydrate metabolism.

A pair of OVARIES is located in the abdomen. The ovary is the primary female sex organ, which produces one ovum during each menstrual cycle, and it also produces two groups of steroid hormones - ESTROGEN and PROGESTERONE. It is composed of ovarian follicles and stromal tissues. Estrogen is synthesised and secreted mainly by the GROWING OVARIAN FOLLICLES, and after ovulation the ruptured follicle is converted to the CORPUS LUTEUM, which secretes mainly PROGESTERONE. Estrogens stimulate the growth and activities of the female secondary sex organs, the development of growing ovarian follicles, the appearance of female secondary sex characters such as a high pitch of voice, and mammary gland development, and they regulate female sexual behaviour. Progesterone SUPPORTS PREGNANCY and acts on the mammary glands, stimulating the formation of ALVEOLI - sac-like structures which store milk - and milk secretion.

The ATRIAL WALL of the heart secretes a peptide hormone, ATRIAL NATRIURETIC FACTOR (ANF), which DECREASES blood pressure - when blood pressure is increased, ANF is secreted and causes DILATION of the blood vessels, which reduces the blood pressure. The JUXTAGLOMERULAR CELLS of the kidney produce a peptide hormone called ERYTHROPOIETIN, which stimulates ERYTHROPOIESIS, the formation of RBC. Endocrine cells in different parts of the gastro-intestinal tract secrete FOUR major peptide hormones - GASTRIN, SECRETIN, CHOLECYSTOKININ (CCK) and GASTRIC INHIBITORY PEPTIDE (GIP). Gastrin acts on the gastric glands and stimulates the secretion of hydrochloric acid and pepsinogen. Secretin acts on the exocrine pancreas and stimulates the secretion of water and bicarbonate ions. CCK acts on both the pancreas and the gall bladder and stimulates the secretion of pancreatic enzymes and bile juice respectively. GIP INHIBITS gastric secretion and motility. Several other non-endocrine tissues secrete hormones called GROWTH FACTORS, which are essential for the normal growth of tissues and their repairing and regeneration.

Hormones produce their effects by binding to specific proteins called HORMONE RECEPTORS located in the TARGET TISSUES ONLY. Membrane-bound receptors are present on the cell membrane of the target cells and intracellular receptors are present inside the target cell, mostly nuclear receptors. Binding forms a HORMONE-RECEPTOR COMPLEX, and each receptor is specific to one hormone only, hence receptors are specific. On the basis of chemical nature, hormones are divided into FOUR GROUPS - (i) peptide, polypeptide and protein hormones, such as insulin, glucagon, pituitary hormones and hypothalamic hormones; (ii) steroids, such as cortisol, testosterone, estradiol and progesterone; (iii) iodothyronines, the thyroid hormones; and (iv) amino-acid derivatives, such as epinephrine. Hormones which interact with membrane-bound receptors normally DO NOT ENTER the target cell, but generate SECOND MESSENGERS - cyclic AMP, IP3\mathrm{IP_3} and Ca2+\mathrm{Ca^{2+}} - which in turn regulate cellular metabolism. Hormones which interact with intracellular receptors - steroid hormones and iodothyronines - mostly regulate GENE EXPRESSION or CHROMOSOME FUNCTION by the interaction of the hormone-receptor complex with the genome, and the cumulative biochemical actions result in physiological and developmental effects.

What Each Section Covers

Nineteen sections, and what each one carries. Use this as the index when you are hunting a fact and do not want to read the whole chapter again.

Section Title What it covers
1 Chemical Coordination - Endocrine Glands and Hormones Why neural coordination alone is not enough - it is fast but short-lived, nerve fibres do not innervate all cells, and cellular functions need continuous regulation; exocrine against endocrine and the meaning of ductless; the classical and the current definitions of a hormone; the list of the organised endocrine bodies and the other organs that also produce hormones.
2 The Hypothalamus The basal part of the diencephalon, forebrain; the neurosecretory cells called nuclei; releasing hormones against inhibiting hormones, with GnRH and somatostatin as the two examples; the route down axons to the portal circulatory system and the anterior pituitary, against the direct neural regulation of the posterior pituitary.
3 The Pituitary Gland - Structure and the Anterior Lobe The sella tursica and the stalk; adenohypophysis and neurohypophysis; pars distalis and pars intermedia; the six hormones of the anterior pituitary - GH, PRL, TSH, ACTH, LH, FSH - with the action of each; the three growth hormone disorders, gigantism, acromegaly and pituitary dwarfism.
4 Pars Intermedia and the Posterior Pituitary The single hormone of the pars intermedia, MSH, and its action on the melanocytes; the pars intermedia almost merged with the pars distalis in humans; the neurohypophysis, which stores and releases but does not make oxytocin and vasopressin; the distal tubules and anti-diuretic action; diabetes insipidus.
5 The Pineal Gland and the Thymus The pineal on the dorsal side of the forebrain and melatonin, which regulates the 24-hour (diurnal) rhythm, the sleep-wake cycle and body temperature; the thymus between the lungs behind the sternum on the ventral side of the aorta, the thymosins, T-lymphocytes and cell-mediated against humoral immunity; the degeneration of the thymus in old individuals.
6 The Thyroid Gland The two lobes, the trachea and the isthmus; follicles and stromal tissues; T4\mathrm{T_4} and T3\mathrm{T_3} and the need for iodine; goitre, cretinism, hyperthyroidism and exophthalmic goitre (Graves' disease) with the direction of each; the four actions of the thyroid hormones; thyrocalcitonin, the protein hormone that lowers blood calcium.
7 The Parathyroid Gland and Calcium Balance The four parathyroid glands on the back side of the thyroid, one pair in each lobe; PTH and its regulation by the circulating levels of calcium ions; the three routes by which PTH raises Ca2+\mathrm{Ca^{2+}} - bone resorption, renal reabsorption and absorption from digested food; PTH as a hypercalcemic hormone working along with TCT.
8 The Adrenal Medulla - The Emergency Hormones One pair of adrenal glands, one above each kidney; the medulla inside and the cortex outside; adrenaline (epinephrine) and noradrenaline (norepinephrine), the catecholamines; the emergency hormones or hormones of fight or flight, and every effect they produce, from alertness and pupilary dilation to the breakdown of glycogen, lipids and proteins.
9 The Adrenal Cortex - The Corticoids The three layers - zona reticularis, zona fasciculata, zona glomerulosa; glucocorticoids with cortisol as the main one and mineralocorticoids with aldosterone as the main one; gluconeogenesis, lipolysis and proteolysis; the actions of cortisol; the reabsorption of Na+\mathrm{Na^+} and excretion of K+\mathrm{K^+} by aldosterone; the androgenic steroids; Addison's disease.
10 The Pancreas and Blood Glucose The pancreas as a composite gland; the Islets of Langerhans, 1 to 2 million of them, 1 to 2 per cent of the tissue; α\alpha-cells and glucagon against β\beta-cells and insulin; glycogenolysis and gluconeogenesis against glycogenesis; hyperglycemic against hypoglycemic; glucose homeostasis maintained jointly; diabetes mellitus and ketone bodies.
11 The Testis The pair in the scrotal sac, outside the abdomen; the dual function - primary sex organ and endocrine gland; seminiferous tubules and interstitial tissue; the Leydig cells in the intertubular spaces; androgens, mainly testosterone, and every action of theirs - the male accessory sex organs, spermatogenesis, the secondary sex characters, libido and the anabolic effects.
12 The Ovary The pair in the abdomen; one ovum in each menstrual cycle; ovarian follicles and stromal tissues; estrogen from the growing follicles against progesterone from the corpus luteum; the actions of estrogens - secondary sex organs, follicle development, high pitch of voice, mammary gland development, sexual behaviour; progesterone supporting pregnancy and forming the alveoli.
13 Hormones of the Heart, Kidney and Gastrointestinal Tract The atrial wall and ANF, which decreases blood pressure by dilating the blood vessels; the juxtaglomerular cells of the kidney and erythropoietin, which stimulates erythropoiesis; the four gastrointestinal hormones - gastrin, secretin, CCK and GIP - and what each acts on, with GIP the only one that inhibits; the growth factors from non-endocrine tissues.
14 The Hormone Index - Gland, Hormone, Action and Disorder The chapter read backwards. The chain of command from hypothalamus to pituitary to peripheral gland; Grid 1, every hormone with its gland, chief action and disorder; Grid 2, the disorder index, disorder first; Grid 3, the pairs that push against each other - insulin against glucagon, PTH against TCT, releasing against inhibiting, aldosterone against ANF.
15 The Mechanism of Hormone Action Hormone receptors in the target tissues only; membrane-bound against intracellular receptors; the hormone-receptor complex and the specificity of each receptor; the four chemical groups of hormones; the second messengers - cyclic AMP, IP3\mathrm{IP_3} and Ca2+\mathrm{Ca^{2+}} - against the regulation of gene expression or chromosome function through the genome.
16 Important Questions and Answers The full worked set for the chapter - the definitions and the gland map, the hypothalamus and the pituitary, the thyroid, parathyroid and thymus, the adrenal and the pancreas, the gonads and the diffuse endocrine tissues, and the mechanism of hormone action.
17 NEET Corner - Chemical Coordination and Integration the NEET Way The chapter rewritten for the NEET pattern - the four shapes this chapter is asked in, the address table of every hormone, the disorder table with name, gland and direction, the negatives and the pairs that get swapped, and a true-or-false drill.
18 NEET-Pattern Practice Questions Forty-four exam-pattern questions covering the whole chapter in proportion, including assertion-and-reason items, 'which is incorrect' items, match-the-column items and items that turn on the direction of a disorder, with pacing and guessing advice.
19 Summary and Exam Tips This page - the chapter in one page, a section-by-section map, the complete gland-hormone-action-disorder table, the exam tips, the last-minute revision list, and a closing set of worked examples.

The chapter has one natural break near the end. Sections 1 to 13 are the grid, gland by gland, taken from the head downwards - hypothalamus, pituitary, pineal, thyroid, parathyroid, thymus, adrenal, pancreas, gonads, and then the heart, kidney and gut. Section 14 turns that grid round and reads it backwards. Section 15 is the only mechanism in the chapter. Sections 16 to 19 are the practice and the revision. If you have time for one half only, revise the grid, because it carries about four fifths of the marks - but do not skip section 15, because the mechanism items are the ones a student who has only memorised the grid will always drop.

The Complete Gland, Hormone, Action and Disorder Table

The whole chapter as one grid. Where the chapter names no disorder for a hormone, the last column is left blank - that is information too, and inventing an entry there is how marks get lost.

Gland or tissue Hormone What it does What goes wrong, and in which direction
Hypothalamus Releasing hormones, e.g. GnRH Stimulate secretion of pituitary hormones; GnRH stimulates pituitary synthesis and release of the gonadotrophins -
Hypothalamus Inhibiting hormones, e.g. somatostatin Inhibit secretions of pituitary hormones; somatostatin inhibits the release of growth hormone -
Pars distalis, anterior pituitary Growth hormone (GH) Growth and development of the somatic tissues Gigantism - OVER, in the growing years; acromegaly - EXCESS in adults, especially middle age; pituitary dwarfism - LOW
Anterior pituitary Prolactin (PRL) Regulates the growth of the mammary glands and the formation of milk in them -
Anterior pituitary Thyroid stimulating hormone (TSH) Stimulates the synthesis and secretion of thyroid hormones from the thyroid gland -
Anterior pituitary Adrenocorticotrophic hormone (ACTH) Stimulates the synthesis and secretion of glucocorticoids from the adrenal cortex -
Anterior pituitary Luteinizing hormone (LH) Males: stimulates synthesis and secretion of androgens from the testis. Females: induces ovulation of the fully mature graafian follicle and maintains the corpus luteum -
Anterior pituitary Follicle stimulating hormone (FSH) Males: with androgens, regulates spermatogenesis. Females: stimulates the growth and development of the ovarian follicles -
Pars intermedia Melanocyte stimulating hormone (MSH) Acts on the melanocytes and regulates the pigmentation of the skin -
Posterior pituitary - stores and releases only; made by the hypothalamus Oxytocin Acts on the smooth muscles and stimulates their contraction - vigorous contraction of the uterus at child birth and milk ejection from the mammary gland -
Posterior pituitary - stores and releases only; made by the hypothalamus Vasopressin (ADH) Acts at the kidney and stimulates resorption of water and electrolytes by the DISTAL TUBULES, reducing loss of water through urine Diabetes insipidus - UNDER, from impaired synthesis or release of ADH, giving water loss and dehydration
Pineal Melatonin Regulates the 24-hour (diurnal) rhythm - the sleep-wake cycle and body temperature; also influences metabolism, pigmentation, the menstrual cycle and our defense capability -
Thyroid, follicular cells Thyroxine or tetraiodothyronine (T4\mathrm{T_4}) and triiodothyronine (T3\mathrm{T_3}) Regulate the basal metabolic rate; support red blood cell formation; control the metabolism of carbohydrates, proteins and fats; maintain water and electrolyte balance Goitre - UNDER, from iodine deficiency; cretinism - UNDER, from hypothyroidism during pregnancy; hyperthyroidism and exophthalmic goitre (Graves' disease) - OVER
Thyroid Thyrocalcitonin (TCT) A protein hormone which regulates the blood calcium level by DECREASING it -
Parathyroid, four glands Parathyroid hormone (PTH) HYPERCALCEMIC - increases the Ca2+\mathrm{Ca^{2+}} level of the blood by bone resorption, reabsorption of Ca2+\mathrm{Ca^{2+}} by the renal tubules and increased absorption from digested food -
Thymus Thymosins Differentiation of T-lymphocytes, giving cell-mediated immunity; also promote the production of antibodies for humoral immunity The thymus is degenerated in old individuals, thymosin production falls and immune responses become weak
Adrenal medulla Adrenaline (epinephrine) and noradrenaline (norepinephrine), the catecholamines Emergency hormones of fight or flight - alertness, pupilary dilation, piloerection, sweating; increased heart beat, strength of heart contraction and rate of respiration; breakdown of glycogen giving increased blood glucose; breakdown of lipids and proteins -
Adrenal cortex Glucocorticoids, chiefly cortisol Gluconeogenesis, lipolysis and proteolysis; inhibit cellular uptake and utilisation of amino acids; cortisol maintains the cardio-vascular system and kidney functions, produces anti-inflammatory reactions, suppresses the immune response and stimulates RBC production Addison's disease - UNDER-production by the adrenal cortex, giving acute weakness and fatigue
Adrenal cortex Mineralocorticoids, chiefly aldosterone Act at the renal tubules - reabsorption of Na+\mathrm{Na^+} and water, excretion of K+\mathrm{K^+} and phosphate ions; maintain electrolytes, body fluid volume, osmotic pressure and blood pressure -
Adrenal cortex Androgenic steroids, small amounts Growth of axial hair, pubic hair and facial hair during puberty -
Pancreas, α\alpha-cells of the Islets of Langerhans Glucagon HYPERGLYCEMIC - acts on the hepatocytes, stimulates glycogenolysis and gluconeogenesis, reduces cellular glucose uptake and utilisation -
Pancreas, β\beta-cells of the Islets of Langerhans Insulin HYPOGLYCEMIC - acts on hepatocytes and adipocytes, enhances cellular glucose uptake and utilisation, stimulates glycogenesis Diabetes mellitus - from prolonged hyperglycemia, with loss of glucose through urine and formation of ketone bodies; treated with insulin therapy
Testis, Leydig or interstitial cells Androgens, mainly testosterone Male accessory sex organs; muscular growth, facial and axillary hair, aggressiveness, low pitch of voice; major stimulatory role in spermatogenesis; male sexual behaviour (libido); anabolic effects on protein and carbohydrate metabolism -
Ovary, growing ovarian follicles Estrogen Growth and activities of the female secondary sex organs, development of growing ovarian follicles, female secondary sex characters such as a high pitch of voice, mammary gland development, and female sexual behaviour -
Ovary, corpus luteum Progesterone Supports pregnancy; acts on the mammary glands and stimulates the formation of alveoli and milk secretion -
Heart, atrial wall Atrial natriuretic factor (ANF) DECREASES blood pressure - when blood pressure is increased, ANF causes dilation of the blood vessels -
Kidney, juxtaglomerular cells Erythropoietin Stimulates erythropoiesis - the formation of RBC -
Gastro-intestinal tract Gastrin Acts on the gastric glands and stimulates the secretion of hydrochloric acid and pepsinogen -
Gastro-intestinal tract Secretin Acts on the exocrine pancreas and stimulates the secretion of water and bicarbonate ions -
Gastro-intestinal tract Cholecystokinin (CCK) Acts on BOTH the pancreas and the gall bladder and stimulates the secretion of pancreatic enzymes and bile juice respectively -
Gastro-intestinal tract Gastric inhibitory peptide (GIP) INHIBITS gastric secretion and motility - the only one of the four that inhibits -
Various non-endocrine tissues Growth factors Essential for the normal growth of tissues and their repairing and regeneration -

Read the fourth column on its own once. Ten disorders are named in this chapter and every one of them is a triple - the hormone, the gland and the direction. Gigantism, acromegaly and hyperthyroidism and exophthalmic goitre are the OVER faults. Pituitary dwarfism, diabetes insipidus, goitre, cretinism, Addison's disease and diabetes mellitus are the UNDER faults.

Exam Tips - What Gets Asked, What Gets Confused, and How to Write It

What gets asked. Strip the whole chapter down and the questions come in five shapes, and they come in roughly this order of frequency.

  1. Which gland secretes this? "Thymosins are secreted by?" "Erythropoietin is produced by?" The answer is one of a small closed set, and the wrong options are the other real glands of this same chapter. Fix the whole grid, not the individual fact.
  2. What does this hormone do? "Aldosterone acts mainly at?" "What does GIP do to gastric secretion?" Every one of these is one row of the table above. If you can say the row, the matching option is the answer and the other three match nothing.
  3. Which disorder, and in which direction? "Deficiency of iodine causes?" "Excess growth hormone in an adult causes?" Never answer a disorder item without saying the DIRECTION to yourself first - half the wrong options are the same disease with the arrow reversed.
  4. A definition or a count, word for word. The current definition of a hormone; four parathyroid glands; six anterior pituitary hormones; one pars intermedia hormone; three adrenal cortex layers; 1 to 2 million Islets of Langerhans at 1 to 2 per cent of the tissue; four gastrointestinal hormones; four chemical groups of hormones. The chapter's own wording and its own figures are the marking scheme.
  5. A negative, an assertion-and-reason, or a match-the-column. "Which of the following is incorrect?" Read the stem twice - half the marks lost on these are lost by a student who found a true statement and ticked it.

What gets confused. Ten pairs, and they account for most of the marks that go missing while the material is perfectly well known.

  1. Diabetes insipidus against diabetes mellitus. They share a word and nothing else. Insipidus is an ADH fault, the loss is WATER, the result is dehydration. Mellitus is an INSULIN fault, the loss is GLUCOSE through the urine, with KETONE BODIES formed.
  2. Simple goitre against exophthalmic goitre. Both enlarge the thyroid and the directions are opposite. Simple goitre is UNDER - iodine deficiency. Exophthalmic goitre is OVER - a form of hyperthyroidism, with protrusion of the eyeballs, increased basal metabolic rate and weight loss. The protruding eyeballs tell them apart.
  3. Gigantism against acromegaly. Same hormone, same direction, different age. Gigantism is excess GH while the person is still growing; acromegaly is excess GH in adults, especially in middle age, giving severe disfigurement especially of the face.
  4. PTH against thyrocalcitonin. PTH is from the PARATHYROID and RAISES blood Ca2+\mathrm{Ca^{2+}}. TCT is from the THYROID and LOWERS it. The calcium-lowering hormone is the thyroid one, and that is the swap the paper offers.
  5. Insulin against glucagon. Insulin from the β\beta-cells LOWERS blood glucose; glucagon from the α\alpha-cells RAISES it. Both come from the same gland but different cells, so an option saying "two different glands" is wrong.
  6. Adrenal medulla against adrenal cortex. The MEDULLA is central and gives CATECHOLAMINES. The CORTEX is outside it and gives CORTICOIDS. And Addison's disease is a CORTEX fault, not a medulla fault.
  7. Glucocorticoids against mineralocorticoids. Cortisol - carbohydrate metabolism. Aldosterone - water and electrolytes.
  8. Estrogen against progesterone. Estrogen from the GROWING OVARIAN FOLLICLES; progesterone from the CORPUS LUTEUM. The corpus luteum does not make estrogen.
  9. Prolactin against oxytocin. They cooperate, not oppose. PRL FORMS the milk; oxytocin EJECTS it.
  10. The anterior against the posterior pituitary. The anterior lobe is reached by a PORTAL CIRCULATORY SYSTEM and MAKES its six hormones. The posterior lobe is under DIRECT NEURAL regulation and only STORES AND RELEASES two hormones the HYPOTHALAMUS made.

How to write a two-mark answer. Two marks means two marked points, and nothing more is read. Give the name first and the function second, in one sentence each, and stop.

  • Which hormone is called the anti-diuretic hormone, and why? - "VASOPRESSIN is called the anti-diuretic hormone (ADH). It acts mainly at the KIDNEY and stimulates the RESORPTION OF WATER AND ELECTROLYTES BY THE DISTAL TUBULES, which reduces the loss of water through urine."
  • What is thyrocalcitonin? - "Thyrocalcitonin (TCT) is a PROTEIN hormone secreted by the THYROID gland. It regulates the blood calcium level by DECREASING it."
  • Do not open a two-mark answer with a sentence of background. The marker is looking for two specific phrases, and a paragraph of run-up buys nothing.

How to write a five-mark answer. Five marks means five marked points, and the structure is what makes them findable. Three rules.

  1. If the question names a gland, write GLAND, then HORMONE, then ACTION, then DISORDER WITH ITS DIRECTION, in that order. That is four marked points before you have written a sentence of prose, and it is exactly the order the marking scheme reads in. A hormone named without its action scores half.
  2. If the question names a set, write it as a BULLETED LIST with one clause of function against each name. The six hormones of the anterior pituitary, the four gastrointestinal hormones, the four chemical groups of hormones, the three corticoid groups - all four of those are marked name by name, and a paragraph hides the names from the marker even when every one is present.
  3. If the question says "differentiate" or "distinguish", draw a two-column table with a Feature column. Give the same features in the same order on both sides, because a difference is awarded only when both halves of it are on the page. Exocrine against endocrine gland, anterior against posterior pituitary, adrenal medulla against adrenal cortex, insulin against glucagon, PTH against TCT, diabetes insipidus against diabetes mellitus, simple against exophthalmic goitre, membrane-bound against intracellular receptors - eight comparisons in this chapter alone, and every one of them is a table.

Three habits that pay across the whole exercise set. When a count is asked, give the number with its unit of counting - FOUR parathyroid glands, SIX anterior pituitary hormones, THREE cortex layers, 1 to 2 MILLION islets at 1 to 2 PER CENT of the tissue. When the chapter gives two names for one thing, write both - adrenaline or epinephrine, noradrenaline or norepinephrine, vasopressin or ADH, thyroxine or tetraiodothyronine, Leydig cells or interstitial cells, exophthalmic goitre or Graves' disease - because a marking scheme that accepts either will always accept both. And when you name a disorder, name the gland and the direction in the same breath, because that triple is the whole of the mark.

Class 11 has no board paper, but the chapter-end exercises and your school tests are still written answers, marked by a person reading for particular words. Every rule above is about making those words easy to find.

The Night Before - What to Revise, in Order

Read in this order and stop when the list runs out. Nothing new goes in tonight.

  1. The gland-hormone-action grid, said out loud from the head down. Thirty minutes, and the most valuable thirty in the chapter. Hypothalamus - releasing and inhibiting hormones, GnRH and somatostatin. Anterior pituitary - GH, PRL, TSH, ACTH, LH, FSH. Pars intermedia - MSH. Posterior pituitary - oxytocin and vasopressin, stored not made. Pineal - melatonin. Thyroid - T4\mathrm{T_4}, T3\mathrm{T_3} and thyrocalcitonin. Parathyroid - PTH. Thymus - thymosins. Adrenal medulla - adrenaline and noradrenaline. Adrenal cortex - glucocorticoids, mineralocorticoids and androgenic steroids. Pancreas - glucagon from the α\alpha-cells, insulin from the β\beta-cells. Testis - androgens. Ovary - estrogen and progesterone. Heart - ANF. Kidney - erythropoietin. Gut - gastrin, secretin, CCK, GIP. If you can say that list without stopping, most of this paper is already answered.

2. The same list backwards. Ten minutes. Take the hormone and give the gland. That is the direction the paper asks in, and it is the direction the chapter never teaches. Spend longest on the ones that name a target rather than a source - TSH is not made in the thyroid, GnRH is not made in the gonads, ACTH is not made in the adrenal - and on thyrocalcitonin, which comes from the thyroid and not the parathyroid.

  1. The ten disorders, each with its gland and its direction. Fifteen minutes. Gigantism - GH, pituitary, OVER. Acromegaly - GH, pituitary, EXCESS in adults. Pituitary dwarfism - GH, pituitary, LOW. Diabetes insipidus - ADH, UNDER. Goitre - thyroid, UNDER, iodine. Cretinism - thyroid, UNDER, during pregnancy. Hyperthyroidism - thyroid, OVER. Exophthalmic goitre or Graves' disease - thyroid, OVER. Addison's disease - adrenal cortex, UNDER. Diabetes mellitus - insulin, UNDER. Say the direction every single time.

4. The counts. Five minutes. Four parathyroid glands. Six anterior pituitary hormones. One pars intermedia hormone. Two posterior pituitary hormones. Three adrenal cortex layers. Two adrenal tissues. 1 to 2 million Islets of Langerhans, at 1 to 2 per cent of the pancreatic tissue. Four gastrointestinal hormones. Four chemical groups of hormones. Three second messengers. The 24-hour rhythm. Say each number with what it counts, never on its own.

  1. The ten confused pairs from the exam-tips block. Ten minutes. These are the marks you are most likely to lose while knowing the material perfectly well, which makes them the cheapest to save. Spend longest on diabetes insipidus against diabetes mellitus, PTH against thyrocalcitonin, and the anterior against the posterior pituitary.

6. The mechanism of hormone action. Ten minutes, and do not skip it. Receptors are in the target tissues only. Binding forms a hormone-receptor complex. Each receptor is specific to one hormone only. Membrane-bound receptors keep the hormone outside the cell and work through second messengers - cyclic AMP, IP3\mathrm{IP_3} and Ca2+\mathrm{Ca^{2+}}. Intracellular receptors take steroid hormones and iodothyronines to the genome, and they regulate gene expression or chromosome function. Then say the four chemical groups - peptide and protein hormones such as insulin and glucagon; steroids such as cortisol and testosterone; iodothyronines, the thyroid hormones; and amino-acid derivatives such as epinephrine.

7. The definitions, word for word. Five minutes. A hormone - a non-nutrient chemical which acts as an intercellular messenger and is produced in trace amounts. An endocrine gland - a gland that lacks a duct and releases its secretion into the blood, hence a ductless gland. Hypercalcemic - PTH, which raises blood calcium. Hyperglycemic - glucagon, which raises blood glucose.

8. The negatives. Five minutes. The posterior pituitary does not synthesise oxytocin or vasopressin. The hypothalamus does not act on the thyroid or the adrenal directly. The pars intermedia secretes only one hormone. Thyrocalcitonin is not a parathyroid hormone. The adrenal cortex is not the inner tissue. Addison's disease is not a medulla fault. Alpha cells do not secrete insulin. Estrogen is not secreted by the corpus luteum. ANF does not raise blood pressure. GIP is the only gut hormone that inhibits. Membrane-bound hormones do not enter the target cell. Thyroid hormones are not steroids, though they use intracellular receptors like steroids.

If you have ten minutes and no more, say the gland-hormone list from the head down and then say the ten disorders with their directions. This chapter rewards a correctly filed address and a correctly pointed arrow over everything else, and a student who has those two will out-score one who has read the whole chapter through again.

Solved Examples

Question 1

Q. Define an exocrine gland, an endocrine gland and a hormone, using the chapter's own wording.

Answer. An exocrine gland has a duct, and its secretion is carried through that duct onto a surface or into a cavity - the salivary glands and the exocrine part of the pancreas are examples. An endocrine gland LACKS A DUCT and releases its secretion directly into the blood, which is why endocrine glands are called ductless glands. A hormone has two definitions in this chapter. The classical one is a chemical produced by endocrine glands, released into the blood and transported to a distantly located target organ. The current one is that hormones are NON-NUTRIENT CHEMICALS which act as INTERCELLULAR MESSENGERS and are produced in TRACE AMOUNTS, and the reason for widening it is stated plainly - the new definition covers a number of new molecules in addition to the hormones secreted by the organised endocrine glands.

Question 2

Q. Give the three reasons the chapter offers for why the body needs chemical coordination as well as neural coordination.

Answer. 1. Neural coordination is FAST BUT SHORT-LIVED - the impulse arrives, the effect happens, and it is over. 2. The nerve fibres do not innervate all the cells of the body, so a wired system cannot reach everything. 3. The cellular functions need to be continuously regulated, and continuous regulation cannot be run by bursts. Hence a special kind of coordination and integration has to be provided, and this function is carried out by hormones, and the neural system and the endocrine system jointly coordinate and regulate the physiological functions in the body.

Question 3

Q. How does the hypothalamus control the two lobes of the pituitary? Give the route in each case.

Answer. By two completely different routes, and the pair is asked as a contrast.

Anterior pituitary Posterior pituitary
The route Hypothalamic hormones originate in the neurons, pass through axons, are released from the nerve endings and reach the pituitary through a PORTAL CIRCULATORY SYSTEM DIRECT NEURAL regulation by the hypothalamus
What the hypothalamus sends Releasing hormones, which stimulate secretion of pituitary hormones, and inhibiting hormones, which inhibit secretions of pituitary hormones The finished hormones themselves - oxytocin and vasopressin are synthesised by the hypothalamus and transported axonally
What the lobe does Makes its own six hormones Stores and releases two hormones it did not make
Examples GnRH stimulates release of the gonadotrophins; somatostatin inhibits release of growth hormone Oxytocin and vasopressin (ADH)

Question 4

Q. Name the six hormones of the pars distalis and give one clause of function for each.

Answer.

  • Growth hormone (GH) - growth and development of the somatic tissues; over-secretion gives gigantism, low secretion gives pituitary dwarfism, and excess in adults gives acromegaly.
  • Prolactin (PRL) - regulates the growth of the mammary glands and the formation of milk in them.
  • Thyroid stimulating hormone (TSH) - stimulates the synthesis and secretion of thyroid hormones from the thyroid gland.
  • Adrenocorticotrophic hormone (ACTH) - stimulates the synthesis and secretion of the steroid hormones called glucocorticoids from the adrenal cortex.
  • Luteinizing hormone (LH) - a gonadotrophin; in males it stimulates the synthesis and secretion of androgens from the testis, and in females it induces ovulation of the fully mature graafian follicle and maintains the corpus luteum.
  • Follicle stimulating hormone (FSH) - a gonadotrophin; in males it regulates spermatogenesis along with androgens, and in females it stimulates the growth and development of the ovarian follicles.

MSH is not on this list - it belongs to the pars intermedia, which secretes only that one hormone.

Question 5

Q. Why is the posterior pituitary not counted as a gland that makes hormones?

Answer. Because it does not make any. The neurohypophysis, also called the pars nervosa or posterior pituitary, STORES AND RELEASES two hormones, oxytocin and vasopressin, which are actually SYNTHESISED BY THE HYPOTHALAMUS and transported axonally to the neurohypophysis. The hypothalamus is the source; the posterior pituitary is the store and the release point. An option saying that the posterior pituitary synthesises oxytocin is the single most common wrong answer in this part of the chapter.

Question 6

Q. Name the four disorders of the thyroid gland and give the direction of each.

Answer.

Disorder Direction Cause and signs
Goitre UNDER - hypothyroidism Deficiency of iodine in the diet, giving hypothyroidism and enlargement of the thyroid gland
Cretinism UNDER - hypothyroidism Hypothyroidism during pregnancy, giving the baby stunted growth, mental retardation, low intelligence quotient, abnormal skin and deaf-mutism
Hyperthyroidism OVER Cancer of the thyroid gland or development of nodules, raising synthesis and secretion to abnormally high levels
Exophthalmic goitre, also called Graves' disease OVER A form of hyperthyroidism - enlargement of the thyroid gland, protrusion of the eyeballs, increased basal metabolic rate and weight loss

In adult women hypothyroidism may also make the menstrual cycle irregular. The pair that gets confused is simple goitre against exophthalmic goitre: both enlarge the gland, but one is under and the other is over, and the protruding eyeballs are what tell them apart.

Question 7

Q. Which two hormones regulate blood calcium? Give the gland and the direction of each.

Answer. Parathyroid hormone (PTH) comes from the parathyroid glands - four of them, on the back side of the thyroid gland, one pair in each lobe - and it is a HYPERCALCEMIC hormone which increases the Ca2+\mathrm{Ca^{2+}} level of the blood by three routes: it acts on bones and stimulates bone resorption, it stimulates reabsorption of Ca2+\mathrm{Ca^{2+}} by the renal tubules, and it increases Ca2+\mathrm{Ca^{2+}} absorption from the digested food. Its secretion is regulated by the circulating levels of calcium ions. Thyrocalcitonin (TCT) comes from the THYROID gland, is a protein hormone, and regulates the blood calcium level by DECREASING it. Along with TCT, PTH plays a significant role in calcium balance. The trap is the source - the calcium-lowering hormone is the thyroid one.

Question 8

Q. Distinguish between the adrenal medulla and the adrenal cortex.

Answer.

Feature Adrenal medulla Adrenal cortex
Position Centrally located Outside the medulla
Structure One tissue Three layers - zona reticularis (inner), zona fasciculata (middle), zona glomerulosa (outer)
Hormones Adrenaline (epinephrine) and noradrenaline (norepinephrine) - the catecholamines The corticoids - glucocorticoids (chiefly cortisol), mineralocorticoids (chiefly aldosterone) and small amounts of androgenic steroids
When secreted Rapidly, in response to stress of any kind and during emergency situations - the emergency hormones or hormones of fight or flight Continuously, for carbohydrate metabolism and water and electrolyte balance
Main effects Alertness, pupilary dilation, piloerection, sweating; increased heart beat, strength of heart contraction and rate of respiration; breakdown of glycogen, lipids and proteins Gluconeogenesis, lipolysis, proteolysis; cortisol maintains the cardio-vascular system and kidney functions, produces anti-inflammatory reactions, suppresses the immune response and stimulates RBC production; aldosterone reabsorbs Na+\mathrm{Na^+} and water and excretes K+\mathrm{K^+} and phosphate ions
Disorder named - Addison's disease - UNDER-production, giving acute weakness and fatigue

Question 9

Q. How do insulin and glucagon jointly maintain glucose homeostasis?

Answer. They come from the same gland but different cells, and they pull blood glucose in opposite directions. Glucagon is secreted by the α\alpha-cells of the Islets of Langerhans. It acts mainly on the liver cells (hepatocytes) and stimulates glycogenolysis, giving increased blood sugar (hyperglycemia); it also stimulates gluconeogenesis and reduces cellular glucose uptake and utilisation - so it is a HYPERGLYCEMIC hormone. Insulin is secreted by the β\beta-cells. It acts mainly on hepatocytes and adipocytes and enhances cellular glucose uptake and utilisation, giving a rapid movement of glucose from the blood into those cells and decreased blood glucose (hypoglycemia), and it also stimulates the conversion of glucose to glycogen (glycogenesis). Glucose homeostasis is maintained jointly by insulin and glucagon, and prolonged hyperglycemia leads to diabetes mellitus, with loss of glucose through urine and formation of harmful compounds known as ketone bodies; diabetic patients are successfully treated with insulin therapy.

Question 10

Q. Name the hormones of the testis and the ovary, say exactly where each comes from, and give the chief action of each.

Answer.

Gonad Where the hormone is made Hormone Chief action
Testis Leydig cells or interstitial cells, in the intertubular spaces Androgens, mainly testosterone Development, maturation and functions of the male accessory sex organs; muscular growth, facial and axillary hair, aggressiveness, low pitch of voice; major stimulatory role in spermatogenesis; male sexual behaviour; anabolic effects on protein and carbohydrate metabolism
Ovary Growing ovarian follicles Estrogen Growth and activities of the female secondary sex organs, development of growing ovarian follicles, female secondary sex characters such as a high pitch of voice, mammary gland development, and female sexual behaviour
Ovary Corpus luteum, formed from the ruptured follicle after ovulation Progesterone Supports pregnancy; acts on the mammary glands and stimulates the formation of alveoli and milk secretion

The testis performs dual functions - it is a primary sex organ AND an endocrine gland, and the ovary produces one ovum during each menstrual cycle as well as its two steroid hormones.

Question 11

Q. Which hormones come from the heart, the kidney and the gastrointestinal tract, and what does each do?

Answer.

  • Heart. The atrial wall secretes atrial natriuretic factor (ANF), which DECREASES blood pressure - when blood pressure is increased, ANF is secreted, which causes dilation of the blood vessels and reduces the pressure.
  • Kidney. The juxtaglomerular cells produce erythropoietin, which stimulates erythropoiesis - the formation of RBC.
  • Gastrointestinal tract. Endocrine cells in different parts of it secrete four major peptide hormones. Gastrin acts on the gastric glands and stimulates the secretion of hydrochloric acid and pepsinogen. Secretin acts on the exocrine pancreas and stimulates the secretion of water and bicarbonate ions. Cholecystokinin (CCK) acts on both the pancreas and the gall bladder and stimulates the secretion of pancreatic enzymes and bile juice respectively. Gastric inhibitory peptide (GIP) INHIBITS gastric secretion and motility.

GIP is the only one of the four that inhibits, and that single word is what a question on this group usually turns on.

Question 12

Q. Describe the mechanism of hormone action, taking both routes.

Answer. Hormones produce their effects by binding to specific proteins called HORMONE RECEPTORS located in the TARGET TISSUES ONLY. The binding forms a HORMONE-RECEPTOR COMPLEX, and each receptor is specific to one hormone only, hence receptors are specific. There are two kinds of receptor and therefore two routes.

  1. Membrane-bound receptors, present on the cell membrane of the target cells. The hormones that use them - the peptide, polypeptide and protein hormones and the amino-acid derivatives - normally DO NOT ENTER the target cell. Instead they generate SECOND MESSENGERS - cyclic AMP, IP3\mathrm{IP_3} and Ca2+\mathrm{Ca^{2+}} - which in turn regulate cellular metabolism.
  2. Intracellular receptors, present inside the target cell, mostly nuclear receptors in the nucleus. The hormones that use them - the steroid hormones and the iodothyronines - mostly regulate GENE EXPRESSION or CHROMOSOME FUNCTION by the interaction of the hormone-receptor complex with the genome.

In both routes the cumulative biochemical actions result in physiological and developmental effects.

Question 13

Q. Give the four chemical groups into which hormones are divided, with an example of each.

Answer.

Group Examples
Peptide, polypeptide and protein hormones Insulin, glucagon, pituitary hormones, hypothalamic hormones
Steroids Cortisol, testosterone, estradiol, progesterone
Iodothyronines The thyroid hormones
Amino-acid derivatives Epinephrine

The two that get mixed up are the last two. Thyroid hormones are iodothyronines, NOT steroids - but they behave like steroids, because iodothyronines and steroid hormones both use intracellular receptors and act through the genome.

Question 14

Q. In one pass, name every disorder in this chapter with its hormone, its gland and its direction.

Answer.

Disorder Hormone Gland Direction
Gigantism GH Pituitary, pars distalis OVER, in the growing years
Acromegaly GH Pituitary, pars distalis EXCESS in adults, especially middle age
Pituitary dwarfism GH Pituitary, pars distalis LOW
Diabetes insipidus Vasopressin (ADH) Released by the posterior pituitary, made by the hypothalamus UNDER - impaired synthesis or release
Goitre T4\mathrm{T_4} and T3\mathrm{T_3} Thyroid UNDER - iodine deficiency in the diet
Cretinism T4\mathrm{T_4} and T3\mathrm{T_3} Thyroid UNDER - hypothyroidism during pregnancy
Hyperthyroidism T4\mathrm{T_4} and T3\mathrm{T_3} Thyroid OVER - cancer or nodules
Exophthalmic goitre (Graves' disease) T4\mathrm{T_4} and T3\mathrm{T_3} Thyroid OVER - a form of hyperthyroidism
Addison's disease The corticoids Adrenal cortex UNDER-production
Diabetes mellitus Insulin β\beta-cells of the pancreas UNDER - prolonged hyperglycemia

Weak immune responses in old age are not a disease of secretion but a consequence of structure - the thymus is degenerated in old individuals, so thymosin production falls.

This is the closing section of the last chapter of Class 11 Biology, so the grid above is the last thing worth revising from the whole book - read it in both directions, and say the direction of every disorder out loud.