Which of the following suppress(es) the secretion of ACTH?

Correct Answer: D

Rationale: Elevated plasma cortisol levels suppress the secretion of ACTH through negative feedback. High cortisol levels signal the hypothalamus and pituitary to decrease the release of CRH and ACTH, respectively, to maintain homeostasis. This is a regulatory mechanism to prevent excessive cortisol production. A: Elevated blood glucose levels do not directly suppress ACTH secretion. B: Dietary iodine is not related to ACTH secretion. C: CRH stimulates ACTH release, so it does not suppress its secretion.

Correct Answer: D

Rationale: The correct answer is D because both Cushing syndrome and Addison's disease are disorders of the adrenal cortex. Cushing syndrome involves excessive cortisol production, while Addison's disease is characterized by insufficient cortisol production. Both conditions directly affect the adrenal cortex, leading to hormonal imbalances. Choice A is incorrect because Cushing syndrome involves hyperfunction, not hypofunction. Choice B is incorrect as it states hypersecretion, which is true for Cushing syndrome but not for Addison's disease. Choice C is incorrect because while replacement cortisol therapy is used for Addison's disease, it is not the only treatment option, and it does not apply to Cushing syndrome.

Correct Answer: C

Rationale: The correct answer is C because epinephrine stimulates the hepatic conversion of glycogen into glucose. This process, called glycogenolysis, releases stored glucose from the liver into the bloodstream, increasing blood glucose levels. Choice A is incorrect because epinephrine does not directly increase glucose transport into cells. Choice B is incorrect as gluconeogenesis is the synthesis of new glucose, not the release of stored glucose. Choice D is incorrect because fatty acids are not directly converted into glucose by epinephrine.

Correct Answer: A

Rationale: Step 1: Calcitonin is secreted by the thyroid gland and lowers blood calcium levels by promoting calcium deposition in bones. Step 2: Parathyroid hormone (PTH) is secreted by the parathyroid gland and raises blood calcium levels by stimulating bone resorption and increasing calcium reabsorption in the kidneys. Step 3: Since Calcitonin lowers blood calcium and PTH raises blood calcium, choice A is correct. Summary: Choices B, C, and D are incorrect as they provide inaccurate information about the roles of calcitonin, PTH, thyroxine, and triiodothyronine in regulating blood calcium levels.

Correct Answer: D

Rationale: The correct answer is D: pituitary gland. The pituitary gland is often referred to as the 'master gland' because it controls the functions of other endocrine glands in the body. It secretes hormones that regulate various bodily functions such as growth, metabolism, and reproduction. It is located at the base of the brain and is divided into two parts: anterior and posterior. The anterior pituitary gland produces and releases several important hormones that influence other endocrine glands. The other choices (A: pancreas, B: adrenal glands, C: thyroid gland) do not have the same broad regulatory control over the endocrine system as the pituitary gland.