Which of the following are not influenced by parathyroid hormone?

Correct Answer: D

Rationale: Parathyroid hormone (PTH) targets kidneys (Ca²⁺ reabsorption), bones (Ca²⁺ release), and intestines (via vitamin D for Ca²⁺ uptake) to raise blood calcium. Muscles aren't direct targets PTH doesn't alter their function, though low calcium from PTH absence causes tetany indirectly. 'None' is incorrect PTH affects listed organs. Muscles' exclusion distinguishes them, key to PTH's calcium-focused action, unlike regulated sites.

Correct Answer: A

Rationale: Elevated ACTH from the anterior pituitary stimulates the adrenal cortex's zona fasciculata to release glucocorticoids (e.g., cortisol), regulating stress and metabolism. Mineralocorticoids (e.g., aldosterone) from zona glomerulosa respond to renin-angiotensin, not ACTH primarily. Epinephrine, from the adrenal medulla, isn't ACTH-driven sympathetic signals control it. Insulin, pancreatic, counters glucose, unrelated to ACTH. Glucocorticoids' ACTH dependency distinguishes them, key to the hypothalamic-pituitary-adrenal axis, unlike electrolyte, medullary, or glucose responses.

Correct Answer: B

Rationale: Paracrine signaling involves chemicals, like prostaglandins, affecting nearby cells, as in inflammation. Autocrine signals target the secreting cell itself (e.g., cancer cells), endocrine signals travel via blood to distant targets, and 'neuron' isn't a signaling type neurons use neurotransmitters. Paracrine's local action distinguishes it, key for short-range cellular communication, contrasting with self-directed or systemic signaling in physiological responses.

Correct Answer: B

Rationale: Thyroid-stimulating hormone (TSH) from the anterior pituitary stimulates thyroid hormone (T3/T4) release, regulated by hypothalamic TRH. TSH isn't hypothalamic, thyroxine isn't pituitary-made, and thyroglobulin is a thyroid storage protein, not a controller. TSH's pituitary origin distinguishes it, central to the hypothalamic-pituitary-thyroid axis, critical for metabolic regulation.

Correct Answer: B

Rationale: Pinealocytes in the pineal gland secrete melatonin to regulate sleep-wake cycles, influenced by light. Melanocytes produce pigment, suprachiasmatic nucleus cells regulate circadian rhythms but don't secrete melatonin, and retinal cells detect light. Pinealocytes' secretory role distinguishes them, vital for circadian control, contrasting with pigment or regulatory cells.