Endocrine System — Set 1

Correct Answer: D. Pituitary

• **Pituitary** = The pituitary gland is called the 'Master Gland' because it secretes hormones that directly control all other major endocrine glands in the body. • **Key fact** — It is a pea-sized gland located at the base of the brain in a bony cavity called the sella turcica and is divided into anterior and posterior lobes. • The hypothalamus regulates pituitary activity through releasing and inhibiting hormones. • 💡 Option A (Pancreas) is wrong because it regulates blood sugar, not other glands; Option B (Thyroid) is wrong because it only controls metabolism; Option C (Adrenal) is wrong because it responds to ACTH signals rather than commanding them.

Correct Answer: A. Adrenaline

• **Adrenaline** = Adrenaline (epinephrine) is secreted by the adrenal medulla and triggers the fight-or-flight response by rapidly increasing heart rate, dilating airways, and releasing glucose into the blood. • **Key fact** — It acts within seconds of a perceived threat, making it one of the fastest-acting hormones in the body; it is also used medically to treat anaphylaxis. • Both adrenaline and noradrenaline are catecholamines derived from the amino acid tyrosine. • 💡 Option B (Thyroxine) is wrong because it regulates long-term metabolism, not acute stress reactions; Option C (Insulin) is wrong because it lowers blood sugar; Option D (Melatonin) is wrong because it regulates sleep, not stress response.

Correct Answer: C. Iodine

• **Iodine** = Iodine is the essential mineral required for synthesising the thyroid hormones T3 (triiodothyronine) and T4 (thyroxine); when dietary iodine is insufficient, the thyroid gland enlarges in an attempt to trap more iodine, resulting in Goitre. • **Key fact** — India mandates iodisation of common salt under the National Iodine Deficiency Disorders Control Programme to prevent Goitre and cretinism in children. • Severe iodine deficiency in pregnant women can cause permanent intellectual disability in the foetus. • 💡 Option A (Sodium) is wrong because its deficiency causes hyponatremia, not Goitre; Option B (Calcium) is wrong because calcium deficiency causes rickets and tetany; Option D (Iron) is wrong because iron deficiency causes anaemia, not thyroid swelling.

Correct Answer: C. Melatonin

• **Melatonin** = Melatonin is secreted by the pineal gland (located in the centre of the brain) in response to darkness, signalling the body to prepare for sleep and setting the circadian rhythm. • **Key fact** — Melatonin secretion is inhibited by blue light, which is why screen exposure at night disrupts sleep; it is synthesised from serotonin. • The pineal gland was historically called the 'third eye' by René Descartes. • 💡 Option A (Progesterone) is wrong because it maintains pregnancy, not sleep; Option B (Serotonin) is wrong because serotonin is the precursor to melatonin and mainly regulates mood; Option D (Oxytocin) is wrong because it stimulates uterine contractions and social bonding.

Correct Answer: A. Pancreas

• **Pancreas** = The pancreas contains clusters of cells called the Islets of Langerhans — beta cells secrete insulin (which lowers blood glucose) and alpha cells secrete glucagon (which raises blood glucose), maintaining sugar homeostasis. • **Key fact** — Failure of insulin secretion or action leads to Diabetes Mellitus, one of the most prevalent metabolic disorders worldwide; insulin was first isolated in 1921 by Banting and Best. • The pancreas is both exocrine (digestive enzymes) and endocrine (hormones), making it a unique dual-function organ. • 💡 Option B (Spleen) is wrong because it filters blood and stores immune cells, not hormones; Option C (Kidney) is wrong because it secretes erythropoietin and renin, not insulin; Option D (Liver) is wrong because it stores glycogen but does not secrete these hormones.

Correct Answer: B. Antidiuretic Hormone

• **Antidiuretic Hormone** = ADH (also called vasopressin) is produced by the hypothalamus, stored in the posterior pituitary, and acts on the kidneys to increase water reabsorption in the collecting ducts, preventing excessive water loss through urine. • **Key fact** — When ADH is deficient or non-functional, the condition Diabetes Insipidus develops, causing the person to produce up to 20 litres of dilute urine per day. • Alcohol suppresses ADH, which is why consuming alcohol leads to increased urination and dehydration. • 💡 Option A (Prolactin) is wrong because it stimulates milk production, not water retention; Option C (Estrogen) is wrong because it is a sex hormone governing female development; Option D (Calcitonin) is wrong because it lowers blood calcium, not regulates water.

Correct Answer: B. Glucagon

• **Glucagon** = The Islets of Langerhans are clusters of endocrine cells in the pancreas — alpha cells (about 20%) specifically secrete glucagon, which raises blood glucose by breaking down glycogen stored in the liver. • **Key fact** — The beta cells in the same Islets secrete insulin, which has the opposite effect; delta cells secrete somatostatin, which inhibits both insulin and glucagon. • The name 'Islets of Langerhans' honours German pathologist Paul Langerhans who discovered them in 1869. • 💡 Option A (Somatostatin) is wrong because it is secreted by delta cells and inhibits other islet hormones; Option C (Insulin) is wrong because insulin is secreted by beta cells; Option D (Gastrin) is wrong because it is a gastrointestinal hormone that stimulates stomach acid.

Correct Answer: B. Thymus

• **Thymus** = The thymus is a bilobed gland located in the upper chest (mediastinum) that secretes the hormone thymosin, which stimulates the maturation of T-lymphocytes (T-cells) essential for cell-mediated immunity. • **Key fact** — The thymus is largest and most active during childhood; it gradually shrinks (involutes) after puberty and becomes largely fatty tissue in adults. • Children with a defective thymus suffer from DiGeorge syndrome, marked by severe immune deficiency. • 💡 Option A (Adrenal) is wrong because it secretes cortisol, adrenaline, and aldosterone, not thymosin; Option C (Pituitary) is wrong because it controls other glands through tropic hormones; Option D (Parathyroid) is wrong because it regulates blood calcium, not immunity.

Correct Answer: A. Thyroxine

• **Thyroxine** = Exophthalmic Goitre (Graves' disease) is an autoimmune condition in which antibodies mimic TSH and stimulate the thyroid to overproduce thyroxine; the resulting excess thyroxine accelerates metabolism and causes the characteristic eyeball protrusion (exophthalmos). • **Key fact** — Excess thyroxine also causes weight loss, rapid heartbeat, heat intolerance, and anxiety — all symptoms of hyperthyroidism; Graves' disease is the most common cause of hyperthyroidism. • The exophthalmos occurs due to swelling of the tissue and muscles behind the eyes, not the hormone acting on the eyes directly. • 💡 Option B (Cortisol) is wrong because excess cortisol causes Cushing's syndrome, not exophthalmic Goitre; Option C (Growth Hormone) is wrong because its excess causes gigantism or acromegaly; Option D (Aldosterone) is wrong because its excess causes Conn's syndrome with high blood pressure.

Correct Answer: B. Oxytocin

• **Oxytocin** = Oxytocin is nicknamed the 'Birth Hormone' or 'Love Hormone'; it is produced by the hypothalamus and released by the posterior pituitary to stimulate powerful uterine muscle contractions during labour, speeding up childbirth. • **Key fact** — After birth, oxytocin also triggers the milk let-down reflex in breastfeeding and promotes mother-infant bonding as well as social trust between individuals. • Synthetic oxytocin (Pitocin) is commonly used medically to induce or augment labour. • 💡 Option A (Progesterone) is wrong because it actually inhibits uterine contractions to maintain pregnancy; Option C (Vasopressin) is wrong because it regulates water reabsorption in kidneys; Option D (Prolactin) is wrong because it stimulates milk production, not uterine contractions.