Which hormone is produced in the hours of darkness and encourages sleep?

Correct Answer: D

Rationale: Melatonin, from pineal gland, rises in darkness, promoting sleep circadian regulator. Insulin (pancreas) lowers glucose, not sleep-related. Renin (kidneys) starts RAAS, blood pressure focus. Angiotensin (blood) constricts vessels, not sleep-inducing. Melatonin's nocturnal secretion distinguishes it, critical for sleep-wake cycles, unlike glucose, pressure, or vascular hormones.

Correct Answer: C

Rationale: Alpha cells in the pancreatic islets secrete glucagon, raising blood glucose by promoting glycogenolysis and gluconeogenesis, countering beta cells' insulin, which lowers it. Enzymes come from exocrine pancreas acinar cells, not endocrine alpha cells. 'None' ignores glucagon's role. Glucagon's glucose-mobilizing action distinguishes it, essential for metabolic balance, unlike insulin's storage or exocrine functions.

Correct Answer: D

Rationale: Parathyroid hormone (PTH) from parathyroids raises blood calcium by mobilizing it from bones, enhancing kidney reabsorption, and boosting intestinal uptake via vitamin D. Calcitonin, from thyroid C-cells, lowers calcium, depositing it in bones. Heparin (anticoagulant) and dicumarol (similar) affect clotting, not calcium. PTH's calcium-elevating role distinguishes it, essential for homeostasis, unlike bone-depositing or unrelated agents.

Correct Answer: D

Rationale: Glucocorticoids' truths: cortisol is the primary human glucocorticoid, managing stress and glucose; they're secreted by the adrenal cortex's zona fasciculata, regulated by ACTH; in Addison's disease (adrenal insufficiency), their secretion drops, causing metabolic issues. All statements hold cortisol's dominance, fasciculata origin, and Addison's reduction align with physiology. No single statement trumps; their collective accuracy distinguishes them, key to adrenal function understanding.

Correct Answer: A

Rationale: Untreated iodine-deficiency goiter raises TSH secretion low iodine cuts thyroxine (Tâ‚„), prompting pituitary TSH increase to stimulate the thyroid, enlarging it. Thyroxine drops, not rises, due to iodine lack. Temperature and metabolic rate fall (hypothyroidism), not rise, from low Tâ‚„. TSH's compensatory surge distinguishes it, key to goiter's feedback loop, unlike reduced thyroid output or metabolic effects.