Iodine-containing hormones:

Correct Answer: D

Rationale: The correct answer is D because iodine-containing hormones, such as thyroid hormones, regulate the metabolic rate by influencing the body's energy production and utilization. TSH (choice A) is not an iodine-containing hormone but a pituitary hormone that stimulates the thyroid gland to produce thyroid hormones. Hypothalamus releasing hormones (choice B) are not iodine-containing hormones. Steroids (choice C) are a different class of hormones that do not contain iodine. In summary, choice D is correct as iodine-containing hormones play a crucial role in regulating metabolic rate, while the other choices are incorrect as they do not accurately describe this function.

Correct Answer: B

Rationale: The correct answer is B: insulin. Insulin is produced by the pancreas and helps lower blood glucose levels by promoting the uptake of glucose into cells for energy or storage. Glucagon (A) raises blood glucose levels, epinephrine (C) and cortisol (D) also increase blood glucose levels by stimulating the release of glucose from storage sites.

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: A

Rationale: The correct answer is A because the hypothalamus secretes releasing hormones into the portal capillaries, which then travel to the anterior pituitary to regulate hormone secretion. This is known as the hypothalamic-pituitary axis. Choices B and C are incorrect because the hypothalamus is not composed of glandular tissue and it is not called the adenohypophysis. Choice D is incorrect because the connection between the hypothalamus and the neurohypophysis is via the hypothalamic-hypophyseal tract, not through the portal capillaries.

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.