Mole for mole, which of the following has the greatest effect on plasma osmolality?

Correct Answer: C

Rationale: Plasma osmolality is primarily regulated by the concentration of solutes in the blood. Vasopressin, also known as antidiuretic hormone (ADH), plays a key role in regulating water reabsorption in the kidneys, thus affecting plasma osmolality. When plasma osmolality increases, vasopressin is released to increase water reabsorption, leading to a decrease in plasma osmolality. Progesterone, cortisol, and aldosterone do not directly influence water reabsorption and therefore do not have as significant an impact on plasma osmolality as vasopressin.

Correct Answer: D

Rationale: The correct answer is D: hyperthyroidism. Nervousness, increased body temperature, and increased blood pressure are classic symptoms of hyperthyroidism. This condition is characterized by an overactive thyroid gland, leading to an excess production of thyroid hormones. These hormones can cause an increase in metabolism, leading to symptoms such as nervousness, heat intolerance, and elevated heart rate. Diabetes mellitus (A) is not associated with increased body temperature or blood pressure. Hypoglycemia (B) is characterized by low blood sugar levels, leading to symptoms such as dizziness and confusion, not increased body temperature. Hypothyroidism (C) is characterized by an underactive thyroid gland, leading to symptoms such as fatigue, weight gain, and cold intolerance, not increased body temperature or blood pressure.

Correct Answer: D

Rationale: The correct answer is D: low levels of calcium in the blood. When calcium levels drop, the parathyroid gland releases parathyroid hormone (PTH) to increase calcium levels in the blood. This is a negative feedback mechanism to maintain calcium homeostasis. A: TSH from the posterior pituitary gland is incorrect because TSH is involved in regulating thyroid function, not PTH release. B: High levels of calcium in the blood would not stimulate PTH release as the body aims to lower, not raise, calcium levels. C: Calcitonin from the anterior pituitary gland is incorrect because calcitonin is released by the thyroid gland and works to lower blood calcium levels, opposing the action of PTH.

Correct Answer: B

Rationale: The correct answer is B because the hypothalamic-hypophyseal tract is indeed partly contained within the infundibulum, which is a stalk-like structure connecting the hypothalamus to the pituitary gland. This pathway is crucial for the release of hormones from the hypothalamus to the pituitary gland. Choice A is incorrect as the hypophysis and pituitary gland are the same structure. Choice C is incorrect as aldosterone is a hormone produced by the adrenal glands, not related to the hypothalamic-pituitary axis. Choice D is incorrect because prolactin synthesis occurs in the lactotroph cells of the anterior pituitary, not in the hypothalamic-hypophyseal tract.

Correct Answer: D

Rationale: The correct answer is D because the second-messenger mechanism involves the hormone binding to specific receptors on the cell surface, activating G proteins, which then trigger the production of cyclic adenosine monophosphate (cAMP) inside the cell. cAMP acts as a secondary messenger to relay the hormone's signal and initiate a cellular response. Synthesizing more hormone than needed (A) is not related to the mechanism. Increasing basal metabolic rate (B) is not a direct result of the second-messenger system. Not responding to feedback (C) contradicts the regulatory nature of hormone actions.