Endocrine System — Set 6

Correct Answer: B. Adrenal gland

• **Adrenal gland** = paired glands sitting atop each kidney (hence 'ad-renal' = near kidney); the outer cortex secretes steroid hormones (cortisol, aldosterone, androgens) while the inner medulla secretes catecholamines (adrenaline, noradrenaline). • **Key fact** — The adrenal cortex has three distinct zones: zona glomerulosa (aldosterone for sodium/water balance), zona fasciculata (cortisol for stress response), and zona reticularis (androgens for secondary sex characteristics). • Adrenal glands are critical for survival — complete adrenal failure (Addison's disease) causes life-threatening hypotension and electrolyte imbalance. • 💡 Option A (Pituitary) sits at the base of the brain in the sella turcica; Option C (Pancreas) lies behind the stomach with both endocrine and exocrine portions; Option D (Thyroid) is a butterfly-shaped gland in the neck — none have cortex-medulla division atop kidneys.

Correct Answer: B. Adrenaline

• **Adrenaline (Epinephrine)** = the first-line treatment for anaphylaxis; administered by intramuscular injection (EpiPen), it rapidly reverses the life-threatening features of anaphylaxis — bronchospasm (by dilating airways), hypotension (by constricting blood vessels), and urticaria (by stabilising mast cells). • **Key fact** — Adrenaline works within minutes and must be given in the outer thigh muscle (not buttock); delay can be fatal since anaphylaxis can cause complete airway closure and cardiovascular collapse within minutes. • EpiPen auto-injectors contain 0.3 mg (adult) or 0.15 mg (child) of adrenaline for emergency use. • 💡 Option A (Thyroxine) regulates metabolism — it has no emergency bronchodilator effect; Option C (Cortisol) is a slower-acting anti-inflammatory used as second-line treatment, not first; Option D (Insulin) lowers blood sugar and would worsen anaphylactic shock.

Correct Answer: C. Thyroid

• **Thyroid** = the thyroid gland begins developing as early as the 24th day of embryonic life (4th week of gestation), arising from an endodermal outgrowth at the base of the tongue that descends to its final position in the neck — making it the earliest endocrine gland to form. • **Key fact** — The thyroglossal duct, which marks the path of thyroid descent, normally disappears; if it persists, it forms a thyroglossal cyst, the most common midline neck mass in children. • Thyroid hormone produced by the fetal thyroid (functional by week 10–12) is critical for early brain development and skeletal maturation. • 💡 Option A (Adrenal) develops from two tissues around weeks 6–8; Option B (Pancreas) appears at week 5–6 but later; Option D (Pituitary) begins forming around week 4–5 but the thyroid's day-24 origin edges all others.

Correct Answer: C. Secretin

• **Secretin** = the first hormone ever discovered (Bayliss and Starling, 1902); it is secreted by S-cells of the duodenum in response to acidic chyme entering from the stomach, and it signals the pancreas to release bicarbonate (HCO3⁻) to neutralise the acid — protecting the intestinal lining. • **Key fact** — Secretin was also the molecule that introduced the very concept of a 'hormone' into science; William Bayliss and Ernest Starling coined the word 'hormone' in 1905 after working with secretin. • Secretin also inhibits gastrin and gastric acid secretion, functioning as a brake on the stomach once food moves to the duodenum. • 💡 Option A (Insulin) lowers blood glucose; Option B (Glucagon) raises blood glucose by glycogenolysis; Option D (Gastrin) stimulates acid secretion in the stomach — the exact opposite of secretin's role in the duodenum.

Correct Answer: D. Raising blood calcium

• **Raising blood calcium** = Parathyroid Hormone (PTH) is secreted by the parathyroid glands when blood calcium falls; it raises calcium by (1) stimulating osteoclasts to resorb bone, (2) increasing calcium reabsorption in kidney tubules, and (3) activating Vitamin D in the kidneys to boost intestinal calcium absorption. • **Key fact** — PTH and Calcitonin (from thyroid) are antagonists: PTH raises blood calcium, Calcitonin lowers it — together they maintain calcium within the narrow normal range (8.5–10.5 mg/dL) essential for nerve and muscle function. • Hyperparathyroidism causes 'bones, stones, groans, and psychic moans' — fractures, kidney stones, abdominal pain, and psychiatric symptoms from hypercalcaemia. • 💡 Option A (Lowering blood calcium) is Calcitonin's job; Options B and C (raising/lowering blood sugar) are functions of glucagon and insulin respectively — PTH has no direct effect on blood glucose.

Correct Answer: C. Insulin

• **Insulin** = produced and secreted by the beta (β) cells in the islets of Langerhans of the pancreas; released in response to high blood glucose, it facilitates glucose uptake into cells (especially muscle and fat), reduces glucose production in the liver, and promotes glycogen synthesis. • **Key fact** — The islets of Langerhans contain four main cell types: alpha (α) cells make glucagon, beta (β) cells make insulin, delta (δ) cells make somatostatin, and PP cells make pancreatic polypeptide. • Insulin was the first protein to be sequenced (Frederick Sanger, 1951) and the first to be produced by recombinant DNA technology (1982), revolutionising diabetes treatment. • 💡 Option A (Amylase) is a digestive enzyme made by pancreatic acinar cells (exocrine), not islets; Option B (Somatostatin) is made by delta cells, not beta cells; Option D (Glucagon) is made by alpha cells — it is the direct antagonist of insulin.

Correct Answer: B. Kidneys

• **Kidneys** = approximately 90% of erythropoietin (EPO) is produced by peritubular interstitial cells of the renal cortex in response to hypoxia (low oxygen); EPO then travels to the bone marrow and stimulates red blood cell (RBC) production. • **Key fact** — The kidneys act as oxygen sensors: haemoglobin-HIF (Hypoxia Inducible Factor) pathway detects low oxygen and triggers EPO gene transcription — a beautifully integrated feedback loop linking oxygen delivery and RBC production. • Synthetic EPO (recombinant EPO, darbepoetin) is used medically for anaemia in chronic kidney disease and is infamously abused by endurance athletes for performance enhancement (blood doping). • 💡 Option A (Spleen) destroys old RBCs but does not produce EPO; Option C (Bone Marrow) is the target where RBCs are produced — EPO acts here but is not made here; Option D (Liver) produces about 10% of EPO in adults but is the primary source in the fetus.

Correct Answer: C. Pineal gland

• **Pineal gland** = a small pea-sized neuroendocrine gland located at the centre of the brain between the two cerebral hemispheres; it secretes melatonin in a circadian rhythm — increasing at night (darkness) and decreasing in daylight — thereby regulating the sleep-wake cycle and seasonal biological rhythms. • **Key fact** — Melatonin synthesis is inhibited by light via a pathway: retina → retinohypothalamic tract → suprachiasmatic nucleus (SCN) → pineal gland; the SCN in the hypothalamus is the master clock, but the pineal gland executes its hormonal output. • Melatonin supplements are used to treat jet lag, shift-work disorder, and delayed sleep-phase syndrome. • 💡 Option A (Thalamus) relays sensory signals but does not secrete melatonin; Option B (Pituitary) is the master endocrine gland but controls other tropic hormones; Option D (Hypothalamus) houses the SCN (master pacemaker) but does not secrete melatonin — the pineal gland does.

Correct Answer: D. Human Chorionic Gonadotropin

• **Human Chorionic Gonadotropin (hCG)** = produced by trophoblast cells of the developing placenta immediately after implantation; hCG maintains the corpus luteum (preventing menstruation) and doubles every 48–72 hours in early pregnancy — its detection in blood or urine forms the basis of all pregnancy tests. • **Key fact** — Home pregnancy test strips detect beta-hCG using antibodies; hCG is detectable in blood as early as 6–8 days after fertilisation and in urine around 10–14 days, making it the earliest reliable biochemical marker of pregnancy. • Abnormally high hCG can indicate molar pregnancy or Down syndrome; abnormally low hCG may suggest ectopic pregnancy or miscarriage. • 💡 Option A (Estrogen) and Option B (Progesterone) both rise in pregnancy but are not specific pregnancy markers used in standard tests; Option C (Prolactin) rises to prepare for breastfeeding but is not the basis of pregnancy testing.

Correct Answer: A. Pituitary

• **Pituitary** = the pituitary gland (hypophysis) sits in the sella turcica ('Turkish saddle') — a bony fossa in the sphenoid bone at the base of the skull — connected to the hypothalamus above by the pituitary stalk (infundibulum); it is the 'master gland' controlling most other endocrine glands via tropic hormones. • **Key fact** — The pituitary has two distinct lobes: the anterior (adenohypophysis) secretes GH, TSH, ACTH, FSH, LH, and Prolactin; the posterior (neurohypophysis) stores and releases Oxytocin and ADH from hypothalamic neurons. • Pituitary tumours (adenomas) pressing on the optic chiasm (which lies just above the sella) classically cause bitemporal hemianopia — loss of the outer visual fields. • 💡 Option B (Parathyroid) comprises four tiny glands embedded in the back of the thyroid in the neck; Option C (Pineal) is deep within the brain between the thalami; Option D (Thyroid) is a butterfly-shaped gland in the anterior neck — none occupy the sella turcica.