What cells secrete melatonin?

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.

Correct Answer: C

Rationale: Gonads (ovaries, testes) produce steroid hormones testosterone, estrogen, progesterone from cholesterol, acting on nuclear receptors for sex traits and reproduction. Amine hormones (e.g., thyroxine) derive from tyrosine/tryptophan, from thyroid. Peptide hormones (e.g., insulin) are protein-based, from pancreas. Catecholamines (e.g., epinephrine) are adrenal medullary, not gonadal. Steroids' lipid-soluble, genomic action distinguishes them, critical for gonadal endocrine function, unlike amino-acid or peptide classes.

Correct Answer: C

Rationale: Melatonin, from the pineal gland, regulates sleep-wake cycles, peaking in darkness to induce sleep, reducing arousal and cortisol darkness triggers, light inhibits it. The false statement reverses this: light suppresses melatonin, resetting circadian rhythms, while darkness stimulates it. Heat loss and rhythm regulation are true effects; pineal production is accurate. This light-dark dynamic distinguishes melatonin's role, critical for circadian alignment, unlike inverted or correct functions.

Correct Answer: C

Rationale: Addison's disease, adrenocortical insufficiency, causes glucocorticoid/mineralocorticoid deficiency, leading to muscle weakness, tiredness, hypoglycemia (not hyperglycemia), and menstrual issues from cortisol lack. Hyperglycemia aligns with excess cortisol (Cushing's). Hypoglycemia distinguishes Addison's metabolic impact, critical for recognizing adrenal failure, contrasting with sugar-elevating conditions.

Correct Answer: A

Rationale: Endocrine glands (e.g., thyroid) are ductless, releasing hormones into blood for distant targets, while exocrine glands (e.g., sweat) use ducts to surfaces or cavities. Hormones versus waste oversimplifies exocrine products (e.g., saliva) aren't just waste. Both gland types are epithelial, not connective for exocrine. Interconnection isn't universal endocrine glands (e.g., adrenals) act independently, like exocrine. Ductless blood delivery distinguishes endocrine function, key to systemic reach, unlike ducted or mischaracterized traits.