Which of the following is least descriptive of the hypothalamus?

Correct Answer: C

Rationale: The correct answer is C because the hypothalamus does not directly secrete ACTH, TSH, and gonadotropins. It secretes releasing hormones that regulate the secretion of these hormones from the anterior pituitary gland. Choice A and B are correct because the hypothalamus does secrete releasing hormones and controls the anterior pituitary gland. Choice D is incorrect because the hypothalamus synthesizes oxytocin and ADH, which are stored in the posterior pituitary gland.

Correct Answer: D

Rationale: Correct Answer: D Rationale: Calcitonin and parathyroid hormone regulate plasma calcium levels. Calcitonin decreases calcium levels by inhibiting bone breakdown, while parathyroid hormone increases calcium levels by stimulating bone breakdown and increasing calcium reabsorption. Therefore, both hormones work together to maintain calcium homeostasis. The correct answer, choice D, highlights that both hormones control plasma calcium levels. Summary of Other Choices: A: Incorrect. Calcitonin is secreted by the thyroid gland, not the parathyroid glands. B: Incorrect. Calcitonin decreases plasma calcium levels, while parathyroid hormone increases plasma calcium levels. C: Incorrect. Parathyroid hormone increases plasma calcium levels, whereas calcitonin decreases plasma calcium levels.

Correct Answer: D

Rationale: Step 1: Cretinism, myxedema, and Graves' disease are all related to thyroid gland function. Step 2: Cretinism is a congenital hypothyroidism, myxedema is adult hypothyroidism, and Graves' disease is hyperthyroidism. Step 3: Thus, they are all disorders of thyroid gland function. Summary: - Choice A is incorrect because they are not all thyroid hormone deficiency diseases. - Choice B is incorrect because they are not all caused by oversecretion of thyroxine. - Choice C is incorrect because they are not primarily related to calcium imbalances due to lack of calcitonin.

Correct Answer: B

Rationale: The correct answer is B: A benign tumor of the adrenal medulla is called a pheochromocytoma. Pheochromocytomas are tumors that arise from the adrenal medulla, leading to overproduction of catecholamines like adrenaline and noradrenaline. This excess secretion can result in symptoms such as high blood pressure, palpitations, and sweating. Choices A and C are incorrect because a benign tumor of the adrenal medulla typically causes high blood pressure, not low blood pressure or Addison's disease. Choice D is incorrect because excess cortisol secretion is associated with conditions like Cushing's syndrome, not pheochromocytoma.

Correct Answer: B

Rationale: The correct answer is B because as plasma levels of calcium decrease, the parathyroid glands secrete an osteoclastic hormone called parathyroid hormone (PTH). PTH acts to increase calcium levels by stimulating the release of calcium from bones via osteoclasts. Insulin secretion (choice A) is not directly related to calcium levels. The kidneys excreting calcium and phosphorus (choice C) would further decrease calcium levels. Calcitonin (choice D) actually decreases blood calcium levels by inhibiting bone breakdown, so it is not secreted when calcium levels decrease.