Which of the following is most likely to cause the secretion of calcitonin?

Correct Answer: D

Rationale: The correct answer is D: Elevated plasma calcium level. Calcitonin is released from the thyroid gland in response to high levels of calcium in the blood. When plasma calcium levels are elevated, calcitonin is secreted to help regulate calcium homeostasis by promoting calcium deposition in bones. Choices A, B, and C are incorrect because hypocalcemia (low calcium levels), hyperglycemia (high blood sugar levels), and dehydration do not directly stimulate the secretion of calcitonin.

Correct Answer: D

Rationale: The correct answer is D because a deficiency of dietary iodine leads to an insufficient production of thyroid hormones, which can result in the enlargement of the thyroid gland, known as a goiter. This is due to the thyroid gland working harder to try to produce more hormones. A, B, and C are incorrect because a deficiency of dietary iodine does not directly affect plasma calcium levels, blood volume, or the synthesis of calcitonin. These are functions that are primarily regulated by other hormones and factors in the body, not by iodine deficiency.

Correct Answer: A

Rationale: The correct answer is A because the posterior pituitary gland is an extension of the hypothalamus. The hypothalamus produces hormones that are stored and released by the posterior pituitary gland. This connection between the two structures allows for direct neural control over hormone release. Option B is incorrect because the neurohypophysis does not secrete releasing hormones; rather, it releases hormones produced by the hypothalamus. Option C is incorrect because the posterior pituitary gland does not regulate adenohypophyseal function; instead, it stores and releases hormones produced by the hypothalamus. Option D is incorrect because the posterior pituitary gland does not secrete releasing hormones; it releases hormones produced by the hypothalamus.

Correct Answer: B

Rationale: The correct answer is B because a hormone that suppresses gluconeogenesis helps to prevent hyperglycemia by inhibiting the production of glucose in the liver. This hormone regulates blood sugar levels by reducing the formation of new glucose molecules. Choice A is incorrect because increasing renal excretion of sodium and water is related to the regulation of fluid balance, not gluconeogenesis. Choice C is incorrect because causing diuresis involves increasing urine production and is not directly related to suppressing gluconeogenesis. Choice D is incorrect because causing hypocalcemia refers to low levels of calcium in the blood and is not associated with the suppression of gluconeogenesis.

Correct Answer: C

Rationale: The correct answer is C: beta cells. Beta cells in the pancreas secrete insulin, which helps decrease blood glucose levels by facilitating the uptake of glucose into cells for energy production. Delta cells (choice A) secrete somatostatin, which inhibits insulin and glucagon secretion. Alpha cells (choice B) secrete glucagon, which increases blood glucose levels. Choice D is a duplicate of choice C. Therefore, the correct answer is C as beta cells play a crucial role in regulating blood glucose levels through insulin secretion.