Endocrine System — Set 4

Correct Answer: A. Estrogen

• **Estrogen** = the primary female sex hormone produced by the ovaries that maintains secondary sexual characteristics such as breast development, wider hips, and body hair distribution after puberty. • **Key fact** — Estrogen also regulates the menstrual cycle and supports bone density throughout a woman's life. • Without adequate estrogen, secondary characteristics regress — this is why menopause causes significant physical changes. • 💡 Option B (Luteinizing Hormone) triggers ovulation, not maintenance of secondary traits; Option C (Progesterone) prepares the uterus for pregnancy; Option D (Prolactin) stimulates milk production after childbirth.

Correct Answer: A. Growth Hormone

• **Growth Hormone (GH)** = secreted by the anterior pituitary, it stimulates bone elongation and muscle growth; excess GH during childhood — before growth plates close — causes gigantism, leading to abnormally tall stature. • **Key fact** — Gigantism differs from acromegaly: gigantism occurs before puberty when bones still grow in length, while acromegaly occurs in adults after the growth plates have fused. • The tallest recorded person, Robert Wadlow (2.72 m), had gigantism due to pituitary tumour-driven GH excess. • 💡 Option B (Adrenaline) governs fight-or-flight responses; Option C (Insulin) controls blood sugar; Option D (Thyroxine) regulates metabolic rate — none control skeletal height.

Correct Answer: B. Cholecystokinin

• **Cholecystokinin (CCK)** = a peptide hormone secreted by the I-cells of the small intestine in response to fats and proteins; it contracts the gallbladder to release bile and stimulates the pancreas to secrete digestive enzymes. • **Key fact** — CCK also acts on the brain to signal satiety — it is one of the reasons a fatty meal makes you feel full quickly. • The name 'cholecystokinin' literally means 'gallbladder mover' (chole = bile, cysto = sac, kinin = to move). • 💡 Option A (Insulin) lowers blood glucose; Option C (Gastrin) stimulates gastric acid secretion in the stomach; Option D (Secretin) stimulates the pancreas to release bicarbonate, not bile.

Correct Answer: B. Growth Hormone

• **Growth Hormone (GH)** = when overproduced in adults (typically due to a pituitary adenoma), GH causes acromegaly — thickening of bones in hands, feet, jaw, and brow ridges, because adult growth plates have fused and bones can only widen, not lengthen. • **Key fact** — Acromegaly is Latin/Greek for 'large extremities'; diagnosis relies on IGF-1 blood levels and glucose suppression test because GH is pulsatile and single readings are unreliable. • Patients often notice that rings, shoes, and hats no longer fit — a gradual change spanning years. • 💡 Option A (Cortisol) excess causes Cushing's syndrome; Option C (Thyroxine) excess causes hyperthyroidism; Option D (Parathyroid Hormone) excess raises blood calcium — none enlarge bones in the acromegaly pattern.

Correct Answer: A. Kidneys

• **Kidneys** = the final and most important activation step of Vitamin D occurs in the kidneys, which convert 25-hydroxyvitamin D (from the liver) into calcitriol (1,25-dihydroxyvitamin D), the hormonally active form that regulates calcium absorption. • **Key fact** — Calcitriol acts on the intestine to increase calcium uptake, on bones to mobilise calcium, and on the kidneys to retain calcium — making it a master controller of calcium homeostasis. • Patients with chronic kidney disease develop Vitamin D deficiency and secondary hyperparathyroidism because the kidneys can no longer perform this conversion. • 💡 Option B (Liver) performs the first hydroxylation to make 25-OH Vitamin D — a precursor, not the active form; Option C (Skin) produces the precursor under UV light; Option D (Thyroid) has no role in Vitamin D activation.

Correct Answer: D. Luteinizing Hormone

• **Luteinizing Hormone (LH)** = a surge in LH from the anterior pituitary — typically around day 14 of the cycle — directly triggers follicle rupture and egg release (ovulation) from the ovary. • **Key fact** — The LH surge also converts the ruptured follicle into the corpus luteum, which then secretes progesterone to prepare the uterus for implantation. • Home pregnancy ovulation kits detect the LH surge in urine to predict the fertile window 24–36 hours before ovulation. • 💡 Option A (Estrogen) builds the uterine lining and triggers the LH surge indirectly; Option B (Progesterone) maintains the uterine lining after ovulation; Option C (FSH) grows the follicle but does not cause rupture.

Correct Answer: B. Adrenaline and Noradrenaline

• **Adrenaline (Epinephrine) and Noradrenaline (Norepinephrine)** = catecholamines secreted by the adrenal medulla (the inner portion of the adrenal gland) in response to stress, triggering the classic 'fight-or-flight' response — faster heart rate, dilated pupils, increased blood glucose, and redirected blood flow to muscles. • **Key fact** — The adrenal medulla is essentially a modified sympathetic ganglion; its cells (chromaffin cells) are neuroendocrine, releasing hormones directly into blood rather than across a synapse. • Adrenaline has greater effect on heart rate and metabolism; noradrenaline has stronger vasoconstriction effects. • 💡 Option A (Insulin and Glucagon) are from pancreatic islets; Option C (Thyroxine and Calcitonin) are from the thyroid; Option D (Cortisol and Aldosterone) come from the adrenal cortex, not the medulla.

Correct Answer: C. Melanocyte Stimulating Hormone

• **Melanocyte Stimulating Hormone (MSH)** = secreted by the intermediate lobe of the pituitary, MSH binds to melanocortin receptors on melanocytes and stimulates the production and dispersal of melanin pigment, causing skin darkening. • **Key fact** — In Addison's disease (primary adrenal insufficiency), low cortisol triggers excess ACTH and MSH from the pituitary, causing characteristic bronze hyperpigmentation of skin and mucous membranes. • In lower vertebrates like frogs and fish, MSH is critical for rapid colour change (chromatophore expansion). • 💡 Option A (Melatonin) is from the pineal gland and regulates sleep-wake cycles, not skin colour; Option B (Prolactin) stimulates milk production; Option D (Thyroxine) regulates metabolism.

Correct Answer: A. Stunted physical and mental growth

• **Stunted physical and mental growth** = cretinism results from congenital hypothyroidism — insufficient thyroxine during fetal and early infant development — causing irreversible damage to the nervous system, severe intellectual disability, short stature, and delayed bone maturation. • **Key fact** — Thyroid hormone is absolutely essential for normal brain myelination; without it in the first two years of life, intellectual impairment is permanent even if treatment begins later. • Neonatal heel-prick screening (done at birth in hospitals) specifically tests TSH and T4 levels to catch congenital hypothyroidism before symptoms appear. • 💡 Option B (High blood pressure) is not associated with cretinism; Option C (Excessive height) is the opposite — cretinism causes dwarfism; Option D (Bulging eyes/exophthalmos) is a sign of hyperthyroidism (Graves' disease), not deficiency.

Correct Answer: C. Maturation of immune T-cells

• **Maturation of immune T-cells** = Thymosin is secreted by the thymus gland and promotes the differentiation and maturation of T-lymphocytes, the immune cells responsible for cell-mediated immunity against pathogens and cancer cells. • **Key fact** — The thymus is most active during childhood and adolescence; it begins to shrink (involute) after puberty, which is why thymosin levels and T-cell production naturally decline with age, contributing to immunosenescence. • Thymosin alpha-1 (Zadaxin) is clinically used to boost immunity in cancer patients receiving chemotherapy and in HIV treatment. • 💡 Option A (Regulating metabolic rate) is the role of Thyroxine; Option B (Controlling blood calcium) is done by PTH and Calcitonin; Option D (Stimulating RBC production) is done by Erythropoietin.