Endocrine System — Set 2

Correct Answer: B. Calcium

• **Calcium** = The four tiny parathyroid glands embedded in the back of the thyroid secrete Parathyroid Hormone (PTH), which raises blood calcium by stimulating bone resorption, increasing calcium absorption in the intestines, and reducing calcium loss in urine. • **Key fact** — PTH and calcitonin (from the thyroid) work as antagonists: PTH raises blood calcium while calcitonin lowers it, together maintaining precise calcium homeostasis. • Hyperparathyroidism (excess PTH) causes bones to weaken (osteitis fibrosa cystica), while hypoparathyroidism causes painful muscle cramps (tetany). • 💡 Option A (Magnesium) is wrong because magnesium levels are regulated mainly by the kidneys, not parathyroid glands; Option C (Zinc) is wrong because zinc is regulated through intestinal absorption; Option D (Potassium) is wrong because potassium is primarily regulated by aldosterone.

Correct Answer: D. Testosterone

• **Testosterone** = Testosterone is an androgen secreted mainly by the Leydig cells of the testes under the stimulus of LH from the pituitary; it drives secondary sexual characteristics in males — facial hair, voice deepening, increased muscle mass, and enlarged genitalia during puberty. • **Key fact** — Small amounts of testosterone are also produced by the adrenal cortex and ovaries in females, where it contributes to libido and bone strength. • Testosterone is a steroid hormone derived from cholesterol and belongs to the androgen class. • 💡 Option A (Progesterone) is wrong because it is a female sex hormone that prepares the uterus for pregnancy; Option B (Luteinizing Hormone) is wrong because LH triggers testosterone production rather than causing the characteristics itself; Option C (Estrogen) is wrong because it governs female secondary sexual characteristics.

Correct Answer: D. Cortisol

• **Cortisol** = Cushing's syndrome results from chronic excess cortisol — a glucocorticoid from the adrenal cortex — which causes obesity centred on the abdomen and face ('moon face'), purple stretch marks, high blood sugar, muscle weakness, and thinning bones. • **Key fact** — The most common cause of Cushing's syndrome is long-term use of corticosteroid medications (iatrogenic), while endogenous causes include a pituitary tumour secreting excess ACTH (Cushing's disease). • Cortisol is known as the 'stress hormone' and plays a key role in the body's long-term response to stress. • 💡 Option A (Aldosterone) is wrong because its excess causes Conn's syndrome characterised by hypertension and low potassium; Option B (Adrenaline) is wrong because it mediates the acute fight-or-flight response; Option C (Noradrenaline) is wrong because it mainly acts as a neurotransmitter and vasoconstrictor.

Correct Answer: D. Somatostatin

• **Somatostatin** = Somatostatin (also called Growth Hormone-Inhibiting Hormone, GHIH) is secreted by the hypothalamus and delta cells of the pancreas; it directly suppresses the release of Growth Hormone (GH) from the anterior pituitary. • **Key fact** — Somatostatin analogues (such as octreotide) are used medically to treat acromegaly (excess GH in adults) and certain hormone-secreting tumours. • Somatostatin also inhibits the release of insulin, glucagon, TSH, and several gastrointestinal hormones, making it a broad inhibitory regulator. • 💡 Option A (Dopamine) is wrong because it inhibits prolactin, not Growth Hormone; Option B (Ghrelin) is wrong because ghrelin actually stimulates GH release (it is a GH secretagogue); Option C (Thyrotropin/TSH) is wrong because TSH stimulates the thyroid, it does not inhibit Growth Hormone.

Correct Answer: A. Vasopressin

• **Vasopressin** = Vasopressin (ADH) signals the kidney's collecting ducts to reabsorb water; in Diabetes Insipidus, either the posterior pituitary fails to secrete sufficient ADH (central DI) or the kidneys fail to respond to it (nephrogenic DI), resulting in the passage of large volumes of pale, dilute urine and intense thirst. • **Key fact** — Diabetes Insipidus is completely different from Diabetes Mellitus — 'insipidus' means tasteless (dilute urine) while 'mellitus' means honey-sweet (glucose-rich urine); blood sugar is normal in DI. • The condition can be confirmed by a water deprivation test followed by administration of synthetic ADH (desmopressin). • 💡 Option B (Oxytocin) is wrong because oxytocin stimulates labour and milk ejection, not water reabsorption; Option C (Glucagon) is wrong because it raises blood sugar by mobilising liver glycogen; Option D (Insulin) is wrong because its deficiency causes Diabetes Mellitus, not Diabetes Insipidus.

Correct Answer: B. Progesterone

• **Progesterone** = After ovulation, the ruptured follicle transforms into the Corpus Luteum (yellow body), which secretes progesterone to thicken the uterine lining (endometrium), suppress further ovulation, and sustain early pregnancy until the placenta takes over. • **Key fact** — If fertilisation does not occur, the Corpus Luteum degenerates after ~14 days, progesterone falls sharply, and menstruation begins; this cyclic drop is the trigger for the monthly period. • During early pregnancy the Corpus Luteum is maintained by hCG (human chorionic gonadotropin) secreted by the embryo — this is what pregnancy tests detect. • 💡 Option A (Prolactin) is wrong because it stimulates milk production after childbirth, not uterine lining maintenance; Option C (Testosterone) is wrong because it is a male androgen; Option D (Thyroxine) is wrong because it regulates metabolic rate, not the uterine lining.

Correct Answer: C. Dwarfism

• **Dwarfism** = Growth Hormone (GH/somatotropin) from the anterior pituitary is essential for bone elongation during childhood; its deficiency stunts linear growth, leading to pituitary dwarfism where proportions remain normal but adult height is below 147 cm. • **Key fact** — Pituitary dwarfism differs from achondroplasia (genetic dwarfism) in that it can be treated with recombinant GH injections if diagnosed early during childhood. • GH acts by stimulating the liver to produce IGF-1 (Insulin-like Growth Factor 1), which directly promotes bone and muscle growth. • 💡 Option A (Acromegaly) is wrong because it results from GH excess in adults causing enlarged hands, feet, and facial features; Option B (Gigantism) is wrong because it is caused by GH excess during childhood; Option D (Cretinism) is wrong because it results from thyroid hormone (thyroxine) deficiency in infancy, not GH deficiency.

Correct Answer: B. Thyroid

• **Thyroid** = The thyroid gland secretes thyroxine (T4) and triiodothyronine (T3), which set the Basal Metabolic Rate — the minimum energy the body needs at rest for vital functions like breathing, circulation, and cell repair. • **Key fact** — Hypothyroidism (low BMR) causes sluggishness, weight gain, and cold intolerance, while hyperthyroidism (high BMR) causes rapid heartbeat, weight loss, and heat intolerance; the thyroid is the main regulator of metabolic speed. • Thyroxine contains four iodine atoms (T4), and when converted to T3 (three iodine atoms) in tissues, it is about four times more potent. • 💡 Option A (Thymus) is wrong because it secretes thymosin for immune cell maturation, not metabolic control; Option C (Adrenal) is wrong because cortisol and adrenaline from the adrenal gland respond to stress, not set resting metabolic rate; Option D (Pancreas) is wrong because it regulates blood glucose through insulin and glucagon.

Correct Answer: D. Hypothalamus

• **Hypothalamus** = The hypothalamus is the master neuroendocrine regulator — it receives signals from the nervous system and releases releasing/inhibiting hormones (like TRH, CRH, GnRH) that travel through portal blood to the anterior pituitary, commanding it to secrete or stop secreting tropic hormones. • **Key fact** — The hypothalamus also directly manufactures ADH and oxytocin, which are stored in and released from the posterior pituitary; this unique dual role makes it the definitive bridge between the nervous and endocrine systems. • Temperature regulation, hunger, thirst, sleep, and emotions are all governed by the hypothalamus in addition to its hormonal role. • 💡 Option A (Cerebellum) is wrong because the cerebellum coordinates balance and motor movement; Option B (Medulla Oblongata) is wrong because it controls autonomic reflexes like breathing and heart rate; Option C (Thalamus) is wrong because it acts as a sensory relay station, not an endocrine controller.

Correct Answer: A. Atrial Natriuretic Peptide

• **Atrial Natriuretic Peptide** = ANP is secreted by the atrial muscle cells of the heart when blood volume or blood pressure rises too high; it acts on the kidneys to excrete more sodium (natriuresis), which draws water out with it, thereby lowering blood volume and pressure. • **Key fact** — ANP is the body's natural counter to the renin-angiotensin-aldosterone system (RAAS), which raises blood pressure; ANP and RAAS work as opposing regulators of blood pressure. • ANP also dilates blood vessels and suppresses aldosterone secretion, giving it a broad antihypertensive effect. • 💡 Option B (Angiotensin) is wrong because angiotensin II raises blood pressure by causing vasoconstriction and stimulating aldosterone; Option C (Renin) is wrong because renin is an enzyme that begins the RAAS cascade to raise blood pressure; Option D (Aldosterone) is wrong because aldosterone increases sodium retention, which raises blood pressure rather than lowering it.