The posterior pituitary gland receives hormone messages from the hypothalamus via ________.

Correct Answer: B

Rationale: The correct answer is B: neurons that extend from the hypothalamus to the pituitary. The hypothalamus produces hormones that are stored and released by the posterior pituitary gland. This communication is facilitated by specialized neurons that extend from the hypothalamus to the pituitary, forming the hypothalamic-pituitary axis. These neurons release hormones into the bloodstream, which then reach the posterior pituitary gland and stimulate the release of its stored hormones. Choice A is incorrect because the posterior pituitary does not directly receive messages through a capillary network. Choice C is incorrect as Schwann cells are responsible for myelinating peripheral nerves, not hormone communication. Choice D is incorrect because while the hypothalamus communicates with the pituitary gland through neurons, it does not involve a capillary network.

Correct Answer: B

Rationale: The correct answer is B because the bloodstream can carry hormones throughout the body simultaneously, reaching various target cells and organs. This enables a single endocrine hormone to produce responses in multiple parts of the body. In contrast, nerve cells can only target a limited number of cells through direct connections. Choice A is incorrect because endocrine hormones can also target multiple responses, not just one. Choice C is incorrect as the endocrine system and nervous system can interact. Choice D is incorrect as endocrine hormones can have broad effects on multiple target cells.

Correct Answer: D

Rationale: In Graves disease, there is an overproduction of thyroid hormones due to autoimmune stimulation. Thyroid-stimulating hormone (TSH) is decreased because the excessive thyroid hormones suppress its production through negative feedback. A and B are incorrect because both T3 and T4 levels are elevated in Graves disease. C is incorrect as DIT is a precursor to thyroid hormones and its levels may not necessarily be decreased in Graves disease.

Correct Answer: C

Rationale: The correct answer is C: down-regulation. Prolonged exposure to high hormone concentrations can lead to down-regulation, where cells decrease their responsiveness to the hormone by reducing the number of hormone receptors. This is a regulatory mechanism to prevent overstimulation. A: Diabetes mellitus is a chronic condition characterized by high blood sugar levels, usually caused by insulin deficiency or insulin resistance, not directly related to prolonged exposure to high hormone concentrations. B: Cellular inhibition is a broad term that may refer to various cellular processes being inhibited, but it is not a specific phenomenon resulting from prolonged exposure to high hormone concentrations. D: Metabolism of protein kinases is a cellular process involved in signal transduction, but it is not a direct consequence of prolonged exposure to high hormone concentrations.

Correct Answer: B

Rationale: The correct answer is B because the parathyroid glands target the bone and activate osteoclasts to release calcium into the bloodstream. This process helps maintain adequate blood calcium levels. By activating osteoclasts, calcium is released from the bone into the blood, ensuring a balance of calcium levels. A: Blocking the action of growth hormone is unrelated to the function of parathyroid glands in maintaining blood calcium levels. C: Antagonizing the synthesis of calcitonin is not the primary mechanism through which parathyroid glands regulate blood calcium levels. D: Slowing the activity of tissues that require calcium for activity would not help maintain adequate blood calcium levels as it does not address the direct release of calcium from bone by activating osteoclasts.