Which of the following glands is both an endocrine gland and an exocrine gland, except?

Correct Answer: D

Rationale: The pituitary gland is purely endocrine, releasing hormones (e.g., GH, TSH) into blood, lacking exocrine ducts. The pancreas is dual endocrine islets (insulin) and exocrine acini (digestive enzymes). Kidneys are endocrine (erythropoietin, renin) and exocrine (urine via nephrons). Gonads (testes/ovaries) are endocrine (testosterone/estrogen) and exocrine (sperm/eggs via ducts). Pituitary's exclusive endocrine nature distinguishes it, key to its master gland status, unlike dual-function organs.

Correct Answer: B

Rationale: The pineal gland secretes melatonin, peaking in darkness to regulate circadian rhythms like sleep-wake cycles, influenced by retinal light signals. The thymus matures T-cells, not rhythms. Parathyroids control calcium via PTH, not timekeeping. The pituitary, a master gland, doesn't directly manage circadian cycles hypothalamus does via pineal. Pineal's melatonin-driven role distinguishes it, key to biological timing, unlike immune, calcium, or regulatory glands.

Correct Answer: A

Rationale: Thyroid's calcitonin lowers blood calcium, depositing it in bones, while parathyroid hormone (PTH) raises it, mobilizing bone calcium and kidney reabsorption. Reversing this (PTH lowering, calcitonin raising) defies physiology. T3/T4 (thyroxine, triiodothyronine) regulate metabolism, not calcium. Including all thyroid hormones (T3, T4, calcitonin) with PTH overstates only calcitonin pairs with PTH. This antagonistic balance distinguishes calcium regulation, key to skeletal and blood homeostasis.

Correct Answer: B

Rationale: Parathyroid glands regulate blood calcium, raising it via PTH (bone resorption, kidney reabsorption), while thyroid's calcitonin lowers it parathyroid dominates setpoint. Thyroid contributes (calcitonin), but parathyroid drives adjustment. Posterior pituitary (ADH) manages water, not calcium. Adrenal medulla (epinephrine) affects stress, not calcium. Parathyroid's PTH primacy distinguishes it, critical for calcium homeostasis, unlike secondary or unrelated glands.

Correct Answer: B

Rationale: Ovaries produce estrogens and progesterone, driving female reproductive cycles and traits. Testes produce testosterone, adrenals minor sex hormones, and hypothalamus GnRH not estrogens/progesterone. Ovarian production distinguishes these hormones' source, essential for female endocrinology, contrasting with male or regulatory glands.