Calcium level in the blood is regulated by the:

Correct Answer: D

Rationale: The correct answer is D: Both A & B. The thyroid and parathyroid glands work together to regulate calcium levels in the blood. The parathyroid gland releases parathyroid hormone, which increases calcium levels, while the thyroid gland secretes calcitonin, which decreases calcium levels. Therefore, both glands play a crucial role in maintaining calcium homeostasis. Choice A, the thyroid gland, is incorrect as it primarily regulates metabolism. Choice C, the adrenal medulla, is incorrect as it is responsible for releasing adrenaline and noradrenaline, not regulating calcium levels.

Correct Answer: D

Rationale: The correct answer is D, receptor-mediated stimulus. Hormones can be stimulated by hormonal, humoral, or neural factors, but not directly by receptors. Hormonal stimulus involves other hormones triggering hormone release, humoral stimulus involves changing blood levels of ions or nutrients triggering hormone release, and neural stimulus involves direct nerve stimulation triggering hormone release. Receptor-mediated stimulus is not a recognized type of hormone stimulus because hormones do not directly respond to receptors in this context.

Correct Answer: A

Rationale: Aldosterone is the correct answer because it specifically acts on the kidneys to increase the reabsorption of sodium. It is produced by the adrenal glands in response to low blood pressure or low sodium levels. Aldosterone binds to receptors in the kidneys, leading to increased sodium reabsorption and potassium excretion. Angiotensin plays a role in stimulating the release of aldosterone, but it does not directly affect sodium reabsorption. ADH regulates water reabsorption, not sodium. ACTH stimulates the adrenal glands to produce cortisol, not aldosterone. Therefore, aldosterone is the hormone responsible for the reabsorption of sodium in the kidneys.

Correct Answer: B

Rationale: The correct answer is B because free fatty acid mobilization is primarily regulated by cortisol, not dehydroepiandrosterone. Cortisol promotes lipolysis and stimulates the release of free fatty acids from adipose tissue. Dehydroepiandrosterone is a precursor hormone mainly involved in sex hormone production and has minimal effects on free fatty acid mobilization. Choices A, C, and D are correctly paired as gluconeogenesis is stimulated by cortisol, muscle glycogenolysis is regulated by epinephrine, and kaliuresis is induced by aldosterone.

Correct Answer: B

Rationale: The correct answer is B: controls the amount of urine one produces. Antidiuretic hormone (ADH) acts on the kidneys to regulate water reabsorption, thereby controlling the amount of urine produced. It does not control metabolic rate (A), increase blood sugar (C), or control reproduction (D). ADH's main function is to maintain water balance in the body by reducing urine output.