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Chemical Coordination and Integration

NCERT Class 11 · Biology Based on NCERT Class 11 Biology textbook · Free CBSE study kit

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Chapter Notes

Overview
This chapter explains how the endocrine system provides chemical coordination and integration in the human body, complementing the fast but short-lived neural system. It covers all major endocrine glands, their hormones, and the mechanisms of hormone action. The one big idea a student must walk away with is that hormones are non-nutrient chemical messengers that regulate metabolism, growth, development, and homeostasis through specific receptors on target tissues.
Key Concepts (54)
Hormones
Non-nutrient chemicals which act as intercellular messengers and are produced in trace amounts.
e.g. Insulin is a hormone produced by the pancreas that helps lower blood glucose levels after a meal.
Endocrine glands
Ductless glands that secrete hormones directly into the blood.
e.g. The pituitary gland, located in the sella tursica, secretes growth hormone directly into the bloodstream.
Hypothalamus
The basal part of the diencephalon, forebrain, containing neurosecretory cells called nuclei that produce releasing and inhibiting hormones.
e.g. GnRH from the hypothalamus stimulates the pituitary to release gonadotrophins.
Releasing hormones
Hormones produced by the hypothalamus that stimulate the secretion of pituitary hormones.
e.g. Gonadotrophin releasing hormone (GnRH) stimulates the pituitary to release LH and FSH.
Inhibiting hormones
Hormones produced by the hypothalamus that inhibit the secretion of pituitary hormones.
e.g. Somatostatin from the hypothalamus inhibits the release of growth hormone from the pituitary.
Pituitary gland
A gland located in a bony cavity called sella tursica, attached to the hypothalamus by a stalk, divided into adenohypophysis and neurohypophysis.
e.g. The anterior pituitary (pars distalis) secretes GH, PRL, TSH, ACTH, LH, and FSH.
Adenohypophysis
The anterior part of the pituitary gland, consisting of pars distalis and pars intermedia.
e.g. Pars distalis produces growth hormone; pars intermedia secretes MSH.
Neurohypophysis
The posterior part of the pituitary gland (pars nervosa) that stores and releases oxytocin and vasopressin, which are synthesised by the hypothalamus.
e.g. Vasopressin (ADH) is released from the neurohypophysis to reduce water loss through urine.
Growth hormone (GH)
A hormone produced by the pars distalis that stimulates body growth; over-secretion causes gigantism, low secretion causes pituitary dwarfism, and excess in adults causes acromegaly.
e.g. A child with GH deficiency may have stunted growth (pituitary dwarfism).
Prolactin (PRL)
A hormone from the pars distalis that regulates the growth of mammary glands and formation of milk.
e.g. After childbirth, prolactin levels rise to stimulate milk production.
Thyroid stimulating hormone (TSH)
A hormone from the pars distalis that stimulates the synthesis and secretion of thyroid hormones from the thyroid gland.
e.g. Low TSH can lead to hypothyroidism.
Adrenocorticotrophic hormone (ACTH)
A hormone from the pars distalis that stimulates the synthesis and secretion of glucocorticoids from the adrenal cortex.
e.g. ACTH is released in response to stress to increase cortisol production.
Luteinizing hormone (LH)
A gonadotrophin from the pars distalis that in males stimulates androgen synthesis, and in females induces ovulation and maintains corpus luteum.
e.g. LH surge triggers ovulation in the female menstrual cycle.
Follicle stimulating hormone (FSH)
A gonadotrophin from the pars distalis that in males regulates spermatogenesis with androgens, and in females stimulates growth of ovarian follicles.
e.g. FSH is given in fertility treatments to stimulate follicle development.
Melanocyte stimulating hormone (MSH)
A hormone secreted by the pars intermedia that acts on melanocytes and regulates pigmentation of the skin.
e.g. MSH can cause darkening of the skin in certain conditions.
Oxytocin
A hormone from the neurohypophysis that stimulates contraction of smooth muscles, especially uterine contraction during childbirth and milk ejection.
e.g. Oxytocin is often given to induce labour in pregnant women.
Vasopressin (ADH)
A hormone from the neurohypophysis that acts on the kidney to stimulate resorption of water and electrolytes, reducing urine output; also called anti-diuretic hormone.
e.g. ADH deficiency leads to diabetes insipidus, causing excessive water loss and dehydration.
Diabetes Insipidus
A condition caused by impairment in synthesis or release of ADH, resulting in diminished ability of the kidney to conserve water, leading to water loss and dehydration.
e.g. A patient with diabetes insipidus produces large volumes of dilute urine.
Pineal gland
A gland located on the dorsal side of the forebrain that secretes melatonin.
e.g. Melatonin helps regulate the sleep-wake cycle.
Melatonin
A hormone secreted by the pineal gland that regulates 24-hour (diurnal) rhythms such as sleep-wake cycle, body temperature, metabolism, pigmentation, menstrual cycle, and defense capability.
e.g. Melatonin levels rise at night to promote sleep.
Thyroid gland
A gland composed of two lobes on either side of the trachea, interconnected by the isthmus, composed of follicles and stromal tissues; synthesises T3 and T4.
e.g. Iodine deficiency in diet can cause goitre due to hypothyroidism.
Thyroxine (T4)
A hormone synthesised by thyroid follicular cells; tetraiodothyronine.
e.g. T4 is converted to T3 in tissues to regulate metabolism.
Triiodothyronine (T3)
A hormone synthesised by thyroid follicular cells.
e.g. T3 is more potent than T4 in regulating basal metabolic rate.
Goitre
Enlargement of the thyroid gland due to iodine deficiency causing hypothyroidism.
e.g. In regions with iodine-deficient soil, goitre is common.
Cretinism
A condition in children due to hypothyroidism during pregnancy, causing stunted growth, mental retardation, low IQ, abnormal skin, deaf-mutism.
e.g. A child born to a mother with severe iodine deficiency may have cretinism.
Hyperthyroidism
A condition due to increased synthesis and secretion of thyroid hormones, e.g., due to cancer or nodules, leading to exophthalmic goitre (Graves' disease) with protrusion of eyeballs, increased BMR, weight loss.
e.g. A patient with Graves' disease may have a rapid heartbeat and weight loss despite eating well.
Thyrocalcitonin (TCT)
A protein hormone secreted by the thyroid gland that regulates blood calcium levels by decreasing them.
e.g. TCT lowers blood calcium when levels are too high.
Parathyroid gland
Four glands present on the back side of the thyroid gland, secreting parathyroid hormone (PTH).
e.g. PTH increases blood calcium levels.
Parathyroid hormone (PTH)
A peptide hormone that increases Ca2+ levels in blood by acting on bones (bone resorption), renal tubules (reabsorption of Ca2+), and increasing Ca2+ absorption from digested food; a hypercalcemic hormone.
e.g. PTH is released when blood calcium is low.
Thymus
A lobular gland located between lungs behind sternum, secreting thymosins; plays a major role in immune system development.
e.g. Thymus degenerates in old age, weakening immune responses.
Thymosins
Peptide hormones secreted by the thymus that play a major role in differentiation of T-lymphocytes (cell-mediated immunity) and promote antibody production (humoral immunity).
e.g. Thymosins help T-cells mature to fight infections.
Adrenal gland
One pair of glands, one above each kidney, composed of adrenal medulla (inner) and adrenal cortex (outer).
e.g. Adrenal medulla secretes adrenaline during stress.
Adrenal medulla
The centrally located tissue of the adrenal gland that secretes adrenaline (epinephrine) and noradrenaline (norepinephrine), called catecholamines or emergency hormones (Fight or Flight).
e.g. Adrenaline increases heart rate and blood glucose during danger.
Adrenal cortex
The outer part of the adrenal gland, divided into zona reticularis, zona fasciculata, and zona glomerulosa; secretes corticoids (glucocorticoids and mineralocorticoids) and small amounts of androgenic steroids.
e.g. Cortisol is the main glucocorticoid from the adrenal cortex.
Glucocorticoids
Corticoids involved in carbohydrate metabolism; main one is cortisol; stimulate gluconeogenesis, lipolysis, proteolysis, inhibit amino acid uptake, maintain cardiovascular and kidney functions, produce anti-inflammatory reactions, suppress immune response, stimulate RBC production.
e.g. Cortisol is used as an anti-inflammatory drug.
Mineralocorticoids
Corticoids that regulate water and electrolyte balance; main one is aldosterone; stimulates reabsorption of Na+ and water, excretion of K+ and phosphate ions in renal tubules.
e.g. Aldosterone helps maintain blood pressure by retaining sodium.
Addison's disease
A disease caused by underproduction of hormones by the adrenal cortex, altering carbohydrate metabolism, causing acute weakness and fatigue.
e.g. A patient with Addison's disease may have low blood pressure and fatigue.
Pancreas
A composite gland acting as both exocrine and endocrine; endocrine part consists of Islets of Langerhans with alpha-cells (secrete glucagon) and beta-cells (secrete insulin).
e.g. Insulin from beta-cells lowers blood glucose.
Glucagon
A peptide hormone from alpha-cells of pancreas that acts on liver cells to stimulate glycogenolysis and gluconeogenesis, increasing blood sugar (hyperglycemic hormone).
e.g. Glucagon is given in emergencies to raise blood sugar.
Insulin
A peptide hormone from beta-cells of pancreas that acts on hepatocytes and adipocytes to enhance cellular glucose uptake and utilisation, stimulates glycogenesis, decreasing blood glucose (hypoglycemic hormone).
e.g. Diabetic patients take insulin to control blood sugar.
Diabetes mellitus
A complex disorder due to prolonged hyperglycemia, associated with loss of glucose through urine and formation of ketone bodies; treated with insulin therapy.
e.g. Type 1 diabetes is caused by insulin deficiency.
Testis
Primary male sex organ in scrotal sac, composed of seminiferous tubules and interstitial tissue; Leydig cells produce androgens (mainly testosterone).
e.g. Testosterone regulates male secondary sex characteristics.
Androgens
A group of hormones (mainly testosterone) produced by Leydig cells of testis; regulate development and functions of male accessory sex organs, spermatogenesis, male sexual behaviour, anabolic effects on protein and carbohydrate metabolism.
e.g. Testosterone stimulates muscle growth and facial hair.
Ovary
Primary female sex organ in abdomen, producing one ovum per menstrual cycle and secreting estrogen and progesterone.
e.g. Estrogen from growing ovarian follicles regulates female secondary sex characters.
Estrogen
A steroid hormone synthesised and secreted mainly by growing ovarian follicles; stimulates growth of female secondary sex organs, development of ovarian follicles, female secondary sex characters, mammary gland development, and regulates female sexual behaviour.
e.g. Estrogen levels rise during the follicular phase of the menstrual cycle.
Progesterone
A steroid hormone secreted mainly by corpus luteum after ovulation; supports pregnancy, acts on mammary glands to stimulate formation of alveoli and milk secretion.
e.g. Progesterone maintains the uterine lining during pregnancy.
Atrial natriuretic factor (ANF)
A peptide hormone secreted by the atrial wall of the heart that decreases blood pressure by causing dilation of blood vessels.
e.g. ANF is released when blood pressure is high to lower it.
Erythropoietin
A peptide hormone produced by juxtaglomerular cells of the kidney that stimulates erythropoiesis (formation of RBC).
e.g. Erythropoietin is used to treat anaemia in kidney disease.
Gastrin
A peptide hormone from the gastrointestinal tract that acts on gastric glands to stimulate secretion of hydrochloric acid and pepsinogen.
e.g. Gastrin is released when food enters the stomach.
Secretin
A peptide hormone from the gastrointestinal tract that acts on the exocrine pancreas to stimulate secretion of water and bicarbonate ions.
e.g. Secretin neutralises stomach acid in the small intestine.
Cholecystokinin (CCK)
A peptide hormone from the gastrointestinal tract that acts on pancreas and gall bladder to stimulate secretion of pancreatic enzymes and bile juice respectively.
e.g. CCK is released after a fatty meal to aid digestion.
Gastric inhibitory peptide (GIP)
A peptide hormone from the gastrointestinal tract that inhibits gastric secretion and motility.
e.g. GIP slows down stomach emptying after a meal.
Hormone receptors
Specific proteins located in target tissues that bind to hormones; membrane-bound receptors (on cell membrane) or intracellular receptors (mostly nuclear).
e.g. Insulin binds to membrane-bound receptors on liver cells.
Second messengers
Molecules such as cyclic AMP, IP3, Ca++ generated inside the target cell when a hormone interacts with a membrane-bound receptor, regulating cellular metabolism.
e.g. Cyclic AMP acts as a second messenger for many protein hormones.
Formulas & Equations (5)
T4 (tetraiodothyronine) and T3 (triiodothyronine) are synthesised by thyroid follicular cells; iodine is essential for their synthesis.
Reads as: Thyroid hormones T4 and T3 require iodine for synthesis.
Variables: T4 = thyroxine (tetraiodothyronine), T3 = triiodothyronine, iodine = essential dietary element.
Use when: When explaining goitre due to iodine deficiency or thyroid hormone regulation.
⚠ Students often think T3 has more iodine than T4; actually T4 has 4 iodine atoms, T3 has 3.
PTH increases Ca2+ levels in blood; TCT decreases Ca2+ levels in blood.
Reads as: Parathyroid hormone raises blood calcium; thyrocalcitonin lowers blood calcium.
Variables: PTH = parathyroid hormone (hypercalcemic), TCT = thyrocalcitonin (hypocalcemic), Ca2+ = calcium ions.
Use when: In questions about calcium homeostasis or antagonistic hormones.
⚠ Students often confuse PTH and TCT — remember PTH raises calcium, TCT lowers it.
Glucagon: hyperglycemic hormone; Insulin: hypoglycemic hormone.
Reads as: Glucagon increases blood glucose; insulin decreases blood glucose.
Variables: Glucagon = hormone from alpha-cells, Insulin = hormone from beta-cells, blood glucose = concentration of glucose in blood.
Use when: In questions about blood glucose regulation or diabetes.
⚠ Students often think insulin increases blood glucose — it actually decreases it.
Aldosterone: stimulates reabsorption of Na+ and water, excretion of K+ and phosphate ions.
Reads as: Aldosterone causes the kidneys to reabsorb sodium and water, and excrete potassium and phosphate.
Variables: Na+ = sodium ions, K+ = potassium ions, phosphate ions = PO4^3-.
Use when: In questions about electrolyte balance, blood pressure regulation, or mineralocorticoid function.
⚠ Students often think aldosterone only affects sodium — it also affects potassium and phosphate.
ANF: decreases blood pressure by causing dilation of blood vessels.
Reads as: Atrial natriuretic factor lowers blood pressure by widening blood vessels.
Variables: ANF = atrial natriuretic factor, blood pressure = force of blood against vessel walls.
Use when: In questions about heart hormones or blood pressure regulation.
⚠ Students often think ANF increases blood pressure — it actually decreases it.
How It Works
Hypothalamic regulation of pituitary gland
  1. Hypothalamic neurosecretory cells (nuclei) produce releasing hormones (e.g., GnRH) and inhibiting hormones (e.g., somatostatin).
  2. These hormones pass through axons and are released from nerve endings.
  3. They reach the anterior pituitary through a portal circulatory system.
  4. Releasing hormones stimulate secretion of pituitary hormones; inhibiting hormones inhibit secretion.
  5. The posterior pituitary is under direct neural regulation of the hypothalamus; hormones oxytocin and vasopressin are synthesised in hypothalamus and transported axonally to neurohypophysis for storage and release.
💡 The portal circulatory system is only for anterior pituitary; posterior pituitary receives direct neural input.
Mechanism of hormone action (protein hormones)
  1. Protein hormone (e.g., insulin) binds to a membrane-bound receptor on the target cell surface.
  2. Hormone-receptor complex forms on the cell membrane.
  3. The hormone does not enter the cell; instead, it generates second messengers (e.g., cyclic AMP, IP3, Ca++).
  4. Second messengers regulate cellular metabolism and physiological functions.
💡 Protein hormones do not enter the cell — they act via second messengers.
Mechanism of hormone action (steroid hormones)
  1. Steroid hormone (e.g., cortisol, testosterone) diffuses across the cell membrane.
  2. It binds to an intracellular receptor (mostly nuclear receptor) inside the target cell.
  3. Hormone-receptor complex forms and interacts with the genome (DNA).
  4. This regulates gene expression or chromosome function, leading to cumulative biochemical actions and physiological/developmental effects.
💡 Steroid hormones enter the cell and act directly on the genome — no second messengers.
Regulation of blood glucose by insulin and glucagon
  1. When blood glucose is high, beta-cells of pancreas secrete insulin.
  2. Insulin acts on hepatocytes and adipocytes to enhance cellular glucose uptake and utilisation.
  3. Insulin stimulates glycogenesis (conversion of glucose to glycogen) in target cells.
  4. This results in decreased blood glucose levels (hypoglycemia).
  5. When blood glucose is low, alpha-cells of pancreas secrete glucagon.
  6. Glucagon acts on liver cells (hepatocytes) to stimulate glycogenolysis (breakdown of glycogen to glucose).
  7. Glucagon also stimulates gluconeogenesis (formation of glucose from non-carbohydrates).
  8. This results in increased blood glucose levels (hyperglycemia).
💡 Insulin lowers blood glucose; glucagon raises blood glucose — they are antagonistic hormones.
Calcium homeostasis by PTH and TCT
  1. When blood Ca2+ levels are low, parathyroid glands secrete PTH.
  2. PTH acts on bones to stimulate bone resorption (dissolution/demineralisation), releasing Ca2+ into blood.
  3. PTH stimulates reabsorption of Ca2+ by renal tubules, reducing Ca2+ loss in urine.
  4. PTH increases Ca2+ absorption from digested food in the intestine.
  5. This raises blood Ca2+ levels (hypercalcemic effect).
  6. When blood Ca2+ levels are high, thyroid gland secretes TCT (thyrocalcitonin).
  7. TCT lowers blood Ca2+ levels (hypocalcemic effect) by inhibiting bone resorption.
💡 PTH raises calcium, TCT lowers calcium — they are antagonistic in calcium balance.
Adrenal medulla response to stress (Fight or Flight)
  1. In response to stress or emergency, adrenal medulla rapidly secretes adrenaline (epinephrine) and noradrenaline (norepinephrine).
  2. These catecholamines increase alertness, pupilary dilation, piloerection (raising of hairs), and sweating.
  3. They increase heart beat, strength of heart contraction, and rate of respiration.
  4. They stimulate breakdown of glycogen in liver, increasing blood glucose concentration.
  5. They also stimulate breakdown of lipids and proteins.
💡 Adrenaline and noradrenaline are emergency hormones — they prepare the body for fight or flight.
Formation and function of corpus luteum
  1. After ovulation, the ruptured graafian follicle is converted into a structure called corpus luteum.
  2. Corpus luteum secretes mainly progesterone.
  3. Progesterone supports pregnancy and stimulates mammary gland alveoli formation and milk secretion.
💡 Corpus luteum forms after ovulation and secretes progesterone.
Exam Traps — Don't Make These Mistakes
⚠ Confusing anterior and posterior pituitary hormones
✗ Oxytocin and vasopressin are secreted by the anterior pituitary.
→ Oxytocin and vasopressin are actually synthesised by the hypothalamus and stored/released by the posterior pituitary (neurohypophysis). The anterior pituitary secretes GH, PRL, TSH, ACTH, LH, FSH, and MSH.
✓ Oxytocin and vasopressin are synthesised in the hypothalamus and released from the posterior pituitary (neurohypophysis).
⚠ Mixing up hyperglycemic and hypoglycemic hormones
✗ Insulin increases blood glucose levels.
→ Insulin actually decreases blood glucose (hypoglycemic) by enhancing cellular uptake and glycogenesis. Glucagon increases blood glucose (hyperglycemic).
✓ Insulin is a hypoglycemic hormone that lowers blood glucose; glucagon is a hyperglycemic hormone that raises blood glucose.
⚠ Confusing PTH and TCT functions
✗ Parathyroid hormone (PTH) decreases blood calcium levels.
→ PTH is a hypercalcemic hormone that increases blood Ca2+ levels by bone resorption, renal reabsorption, and intestinal absorption. TCT (thyrocalcitonin) decreases blood calcium.
✓ PTH increases blood calcium levels (hypercalcemic); TCT decreases blood calcium levels (hypocalcemic).
⚠ Thinking all endocrine glands are ductless
✗ All glands in the body are ductless.
→ Only endocrine glands are ductless; exocrine glands (e.g., sweat glands, salivary glands) have ducts. The pancreas is a composite gland with both exocrine and endocrine parts.
✓ Endocrine glands are ductless and secrete hormones directly into blood; exocrine glands have ducts.
⚠ Confusing diabetes mellitus and diabetes insipidus
✗ Diabetes insipidus is caused by insulin deficiency.
→ Diabetes insipidus is caused by deficiency of ADH (vasopressin), leading to water loss and dehydration. Diabetes mellitus is caused by insulin deficiency or resistance, leading to hyperglycemia and glucose in urine.
✓ Diabetes insipidus is due to ADH deficiency; diabetes mellitus is due to insulin deficiency or resistance.
⚠ Mixing up glucocorticoid and mineralocorticoid functions
✗ Aldosterone regulates carbohydrate metabolism.
→ Aldosterone is a mineralocorticoid that regulates water and electrolyte balance (Na+ and K+). Glucocorticoids like cortisol regulate carbohydrate metabolism (gluconeogenesis).
✓ Aldosterone (mineralocorticoid) regulates electrolyte balance; cortisol (glucocorticoid) regulates carbohydrate metabolism.
Compare & Contrast
Effect on blood glucose
Insulin
Glucagon
Insulin is hypoglycemic (lowers blood glucose); glucagon is hyperglycemic (raises blood glucose).
Effect on blood calcium levels
PTH (Parathyroid hormone)
TCT (Thyrocalcitonin)
PTH is hypercalcemic (increases blood Ca2+); TCT is hypocalcemic (decreases blood Ca2+).
Origin and release of hormones
Anterior pituitary (Adenohypophysis)
Posterior pituitary (Neurohypophysis)
Anterior pituitary synthesises and secretes its own hormones (GH, PRL, TSH, ACTH, LH, FSH, MSH); posterior pituitary stores and releases hormones (oxytocin, vasopressin) that are synthesised by the hypothalamus.
Hormones secreted and function
Adrenal medulla
Adrenal cortex
Adrenal medulla secretes catecholamines (adrenaline, noradrenaline) for emergency fight-or-flight response; adrenal cortex secretes corticoids (glucocorticoids and mineralocorticoids) for metabolism, electrolyte balance, and stress response.
Exam Focus
Marks pattern: Typically 2-3 MCQs (1 mark each), 1-2 short answer questions (2-3 marks), and 1 long answer question (5 marks) on hormone functions or mechanism of action. Total approximately 8-12 marks.
Most asked: Hormones of pituitary gland and their functions · Thyroid hormones and disorders (goitre, cretinism, Graves' disease) · Pancreatic hormones (insulin and glucagon) and diabetes mellitus · Adrenal hormones (cortisol, aldosterone, adrenaline) and their functions · Calcium homeostasis (PTH and TCT) · Mechanism of hormone action (protein vs steroid hormones) · Hypothalamic-pituitary axis
Don't skip: Compare and contrast insulin and glucagon (3-5 marks); Explain the mechanism of action of protein hormones vs steroid hormones (5 marks); Describe the hormones secreted by the pituitary gland and their functions (5 marks); Explain the role of thyroid hormones and disorders associated with their imbalance (3-5 marks); Describe the regulation of blood glucose by insulin and glucagon (5 marks)
One-Line Revision (read aloud before the exam)
  1. Endocrine glands are ductless and secrete hormones directly into blood.
  2. Hormones are non-nutrient chemicals that act as intercellular messengers in trace amounts.
  3. Hypothalamus produces releasing and inhibiting hormones that regulate the pituitary gland.
  4. Anterior pituitary secretes GH, PRL, TSH, ACTH, LH, FSH, and MSH.
  5. Posterior pituitary stores and releases oxytocin and vasopressin (ADH) synthesised by hypothalamus.
  6. Oxytocin stimulates uterine contraction during childbirth and milk ejection.
  7. Vasopressin (ADH) reduces water loss through urine; its deficiency causes diabetes insipidus.
  8. Pineal gland secretes melatonin, which regulates diurnal rhythms like sleep-wake cycle.
  9. Thyroid gland secretes T3 and T4, which regulate basal metabolic rate; iodine is essential for their synthesis.
  10. Iodine deficiency causes goitre; hypothyroidism in pregnancy causes cretinism.
  11. Hyperthyroidism (Graves' disease) causes exophthalmic goitre with increased BMR and weight loss.
  12. Thyrocalcitonin (TCT) from thyroid lowers blood calcium; PTH from parathyroid raises blood calcium.
  13. Thymus secretes thymosins, which help in T-lymphocyte differentiation and immune response.
  14. Adrenal medulla secretes adrenaline and noradrenaline (catecholamines) for fight-or-flight response.
  15. Adrenal cortex secretes glucocorticoids (cortisol) and mineralocorticoids (aldosterone).
  16. Cortisol stimulates gluconeogenesis, lipolysis, proteolysis, and has anti-inflammatory effects.
  17. Aldosterone stimulates Na+ and water reabsorption and K+ excretion in kidneys.
  18. Pancreatic alpha-cells secrete glucagon (hyperglycemic); beta-cells secrete insulin (hypoglycemic).
  19. Insulin deficiency or resistance causes diabetes mellitus with glucose in urine and ketone bodies.
  20. Testis Leydig cells secrete androgens (testosterone) for male sex characteristics and spermatogenesis.
  21. Ovary secretes estrogen (from follicles) and progesterone (from corpus luteum).
  22. Estrogen regulates female secondary sex characters and menstrual cycle; progesterone supports pregnancy.
  23. Heart secretes ANF, which decreases blood pressure by dilating blood vessels.
  24. Kidney secretes erythropoietin, which stimulates RBC formation (erythropoiesis).
  25. GIT hormones include gastrin, secretin, CCK, and GIP; they regulate digestion.
  26. Protein hormones act via membrane-bound receptors and second messengers (e.g., cAMP).
  27. Steroid hormones enter cells, bind to intracellular receptors, and regulate gene expression.
  28. PTH is hypercalcemic; TCT is hypocalcemic — together they maintain calcium homeostasis.
  29. Glucagon and insulin are antagonistic hormones maintaining blood glucose homeostasis.
  30. The portal circulatory system connects hypothalamus to anterior pituitary for hormone transport.

MCQs — 10 Questions with Answers

Q1. Which of the following is NOT a function of the anterior pituitary?

  • A. Secretion of growth hormone
  • B. Stimulation of thyroid hormone synthesis
  • C. Storage and release of oxytocin ✓
  • D. Secretion of prolactin for milk formation

Answer: C — Oxytocin is stored and released by the posterior pituitary (neurohypophysis), not the anterior pituitary; the anterior pituitary secretes GH, TSH, ACTH, LH, FSH, and PRL.

Q2. Iodine deficiency in the diet leads to goitre because:

  • A. Iodine is essential for normal synthesis of thyroid hormones T3 and T4 ✓
  • B. Iodine prevents TSH secretion from the pituitary
  • C. Iodine reduces calcium absorption in the intestines
  • D. Iodine activates the posterior pituitary

Answer: A — Iodine is a crucial component of thyroid hormones; its deficiency impairs hormone synthesis, leading to increased TSH stimulation and thyroid gland enlargement (goitre).

Q3. The hypothalamus regulates the anterior pituitary through ________, but regulates the posterior pituitary through ________.

  • A. portal blood circulation; direct neural pathways ✓
  • B. direct neural pathways; hormones in the blood
  • C. hormones only; neural impulses only
  • D. both neural and hormonal signals; portal circulation only

Answer: A — Hypothalamic releasing/inhibiting hormones travel via portal blood to regulate the anterior pituitary; the posterior pituitary is under direct neural control via axonal transport of hormones.

Q4. A 45-year-old man develops severe disfigurement of the face with coarse facial features and enlargement of hands and feet. Which hormone disorder is most likely responsible?

  • A. Deficiency of growth hormone
  • B. Excess of growth hormone in adulthood (acromegaly) ✓
  • C. Deficiency of thyroid hormones
  • D. Excess of prolactin

Answer: B — Acromegaly is caused by excess GH in adults and results in severe disfigurement, especially of facial features and enlargement of extremities; gigantism occurs in children, not adults.

Q5. Assertion (A): ADH (vasopressin) promotes water resorption in the kidneys. Reason (R): Diabetes insipidus is caused by excessive ADH production. Choose the correct option:

  • A. Both A and R are true, and R is the correct explanation of A
  • B. Both A and R are true, but R is NOT the correct explanation of A
  • C. A is true but R is false ✓
  • D. A is false and R is true

Answer: C — ADH does promote water resorption (true); however, diabetes insipidus is caused by DEFICIENT ADH production or impaired release, not excessive ADH production (false).

Q6. Which of the following statements about melatonin is correct?

  • A. Melatonin is secreted by the anterior pituitary and regulates growth
  • B. Melatonin is secreted by the pineal gland and regulates circadian rhythms including sleep-wake cycles ✓
  • C. Melatonin inhibits all metabolic processes in the body
  • D. Melatonin is secreted by the thyroid and controls iodine metabolism

Answer: B — Melatonin is produced by the pineal gland and plays a crucial role in regulating 24-hour (diurnal) body rhythms including sleep-wake cycles, body temperature, and metabolism.

Q7. In females, FSH and LH (gonadotrophins) work together to:

  • A. Stimulate growth and development of ovarian follicles (FSH) and induce ovulation and maintain corpus luteum (LH) ✓
  • B. Inhibit ovulation and prevent menstruation
  • C. Stimulate the synthesis of oxytocin from the hypothalamus
  • D. Promote milk secretion from the mammary glands

Answer: A — FSH stimulates ovarian follicle growth and development; LH induces ovulation of mature follicles and maintains the corpus luteum formed after ovulation.

Q8. The portal circulatory system connecting the hypothalamus to the anterior pituitary serves to:

  • A. Transport blood rich in oxygen from the heart to the pituitary
  • B. Carry releasing and inhibiting hormones from the hypothalamus to regulate anterior pituitary secretion ✓
  • C. Return cerebrospinal fluid from the pituitary to the hypothalamus
  • D. Transport axons directly from hypothalamic neurons to pituitary cells

Answer: B — The portal blood system is a specialized circulation that transports hypothalamic releasing and inhibiting hormones directly to the anterior pituitary to regulate its hormone secretion.

Q9. A patient shows symptoms of excessive water loss, severe dehydration, and inability to concentrate urine. If ADH levels are low, the disorder is most likely:

  • A. Hypothyroidism
  • B. Diabetes mellitus
  • C. Diabetes insipidus ✓
  • D. Acromegaly

Answer: C — Diabetes insipidus results from impaired synthesis or release of ADH, causing inability to conserve water and leading to excessive urination and severe dehydration.

Q10. Which hormone is correctly matched with its primary target tissue and effect?

  • A. Prolactin → liver → glucose metabolism
  • B. TSH → thyroid gland → synthesis and secretion of thyroid hormones ✓
  • C. Oxytocin → adrenal cortex → glucocorticoid secretion
  • D. ACTH → pancreas → insulin secretion

Answer: B — TSH (thyroid-stimulating hormone) from the anterior pituitary targets the thyroid gland and stimulates the synthesis and secretion of thyroid hormones (T3 and T4).

Flashcards

What is the modern definition of a hormone?

Hormones are non-nutrient chemicals that act as intercellular messengers and are produced in trace amounts.

Why are endocrine glands called ductless glands?

Endocrine glands lack ducts and release their secretions (hormones) directly into the blood for transport to distant target organs.

What are the two types of hormones produced by the hypothalamus?

Releasing hormones (stimulate pituitary hormone secretion) and inhibiting hormones (inhibit pituitary hormone secretion).

Name the six major hormones secreted by the anterior pituitary.

Growth hormone (GH), prolactin (PRL), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), luteinizing hormone (LH), and follicle-stimulating hormone (FSH).

What is the difference between gigantism and acromegaly?

Gigantism results from excessive GH during childhood causing abnormal overall growth; acromegaly results from excess GH in adults causing disfigurement of facial and body features.

What does ADH (vasopressin) do in the body?

ADH stimulates resorption of water and electrolytes by the distal tubules of the kidney, reducing water loss through urine.

What is diabetes insipidus and what causes it?

Diabetes insipidus is a condition caused by impaired synthesis or release of ADH, resulting in diminished ability to conserve water and leading to dehydration.

What is the role of melatonin in the body?

Melatonin regulates 24-hour (diurnal) rhythms including sleep-wake cycles, body temperature, metabolism, pigmentation, and menstrual cycle.

What is goitre and what causes it?

Goitre is enlargement of the thyroid gland caused by iodine deficiency in the diet, resulting in hypothyroidism.

What is the role of the hypothalamic-pituitary portal circulation system?

The portal blood system carries releasing and inhibiting hormones from the hypothalamus to the anterior pituitary to regulate its hormone secretion.

Important Board Questions

Define a hormone. How does hormonal coordination differ from neural coordination in terms of speed and duration of effects? [2 marks]

Define: non-nutrient intercellular messengers produced in trace amounts. Compare: neural is fast but short-lived; hormonal is slow but long-lasting and affects widespread target cells.

Explain the relationship between the hypothalamus and the anterior pituitary gland. How do hypothalamic hormones regulate anterior pituitary function? Give one example of a releasing hormone and its effect. [5 marks]

Describe portal blood circulation from hypothalamus to anterior pituitary. Explain releasing hormones stimulate and inhibiting hormones suppress pituitary secretion. Example: GnRH stimulates LH and FSH secretion for gonadal activity.

A person suffers from severe growth retardation and stunted physical development during childhood, while another person exhibits excessive growth with abnormally large hands, feet, and facial features after age 40. Compare these two conditions, identify the hormonal defects, explain the physiological basis for the different presentations, and discuss why early detection and treatment of growth hormone disorders is clinically important. [6 marks]

First condition: GH deficiency → pituitary dwarfism (occurs in childhood when growth plates active). Second condition: GH excess in adulthood → acromegaly (growth plates fused, affects soft tissues and bones). Explain: GH acts on bones and soft tissues; effects differ based on growth plate status; early detection allows intervention before disfigurement occurs; long-term acromegaly causes serious complications including premature death.

Assertion-Reason Questions for Chemical Coordination and Integration

Q1. Assertion (A):

The hypothalamus is considered part of both the nervous and endocrine systems.

Reason (R):

The hypothalamus contains neurosecretory cells that produce hormones regulating pituitary function and also receives neural input from other brain regions.

Answer: A — Both A and R are true, and R is the correct explanation of A — The assertion is true because the hypothalamus produces hormones (endocrine function) and is composed of neural tissue with synaptic connections (nervous function). The reason correctly explains why it belongs to both systems—it has dual functions. Both are true and the reason fully explains the assertion.

Q2. Assertion (A):

Posterior pituitary hormones are synthesised in the hypothalamus and transported to the pituitary for storage and release.

Reason (R):

The posterior pituitary lacks hormone-synthesising cells and receives oxytocin and vasopressin via axonal transport from hypothalamic neurons.

Answer: B — Both A and R are true, but R is NOT the correct explanation of A — Both the assertion and reason are factually correct. However, the reason is not the complete explanation for 'why' the assertion is true—it merely restates the mechanism without explaining the functional purpose. A complete explanation would address the neural control pathway or the advantage of this arrangement.

Q3. Assertion (A):

Iodine deficiency results in goitre and stunted growth in newborns.

Reason (R):

Iodine is essential for thyroid hormone synthesis; its deficiency causes hypothyroidism, preventing normal thyroid hormone production required for growth and development.

Answer: A — Both A and R are true, and R is the correct explanation of A — The assertion is true: iodine deficiency causes both goitre (enlarged thyroid attempting to compensate) and cretinism (stunted development if occurring in utero/infancy). The reason correctly explains the mechanism—lack of iodine impairs T3/T4 synthesis, leading to both structural enlargement and functional hypothyroidism affecting growth.

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Case-Based Questions (CBQ) for Chemical Coordination and Integration

Case Study:

A 28-year-old woman visits a fertility clinic complaining of irregular menstrual cycles and inability to conceive for 2 years. Blood tests reveal elevated LH levels, normal FSH levels, and ultrasound shows multiple small follicles in both ovaries without a dominant follicle. Her insulin levels are also elevated. The clinician diagnoses Polycystic Ovary Syndrome (PCOS) and explains that the elevated LH-to-FSH ratio disrupts normal follicle maturation and ovulation.

Q1. Based on the hormonal profile, why does the LH-to-FSH ratio disruption prevent ovulation?

  • A. High LH stimulates premature luteinization of follicles before they mature, preventing the formation of a dominant follicle capable of ovulating
  • B. High LH directly destroys growing follicles through apoptosis
  • C. Low FSH allows excessive androgen production in theca cells, inhibiting estrogen synthesis
  • D. Both A and C ✓

Answer: D

Q2. Which endocrine gland's malfunction or hormone imbalance is primarily responsible for the elevated LH levels in PCOS?

  • A. Thyroid gland producing excess thyroid hormones
  • B. Hypothalamus-pituitary axis showing abnormal GnRH pulsatility or increased LH sensitivity ✓
  • C. Adrenal gland producing excess androgens
  • D. Pancreas producing insufficient insulin-inhibiting hormones

Answer: B

Q3. The patient's elevated insulin levels contribute to PCOS pathology. How does hyperinsulinemia worsen the hormonal imbalance?

  • A. Insulin increases ovarian androgen production, which is converted to estrogen, causing negative feedback on FSH
  • B. Insulin directly inhibits the hypothalamus from releasing GnRH
  • C. Insulin stimulates LH release from the anterior pituitary independent of GnRH
  • D. Elevated insulin reduces SHBG (sex hormone-binding globulin), increasing free androgens and disrupting normal follicle development ✓

Answer: D

Q4. If treatment with FSH injections is initiated to stimulate follicle growth, what is the primary therapeutic goal?

  • A. Increase FSH to suppress LH and restore normal FSH-to-LH ratio for proper follicle maturation
  • B. Replace deficient FSH to allow the development of a single dominant follicle capable of ovulation ✓
  • C. Stimulate the hypothalamus to produce more GnRH
  • D. Inhibit androgen production from ovarian stroma

Answer: B

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