What of the following statements best describes a toxic thyroid adenoma?

Correct Answer: D

Rationale: Step 1: Toxic thyroid adenoma is characterized by a benign tumor in the thyroid gland. Step 2: This tumor produces excessive amounts of thyroid hormones, particularly T3 and T4. Step 3: The tumor arises from the follicular cells of the thyroid gland. Step 4: Choice D accurately describes a toxic thyroid adenoma as a benign tumor producing excessive thyroid hormones from follicular cells. Summary: Choice A is incorrect because it describes autoimmune thyroid disease, not a toxic adenoma. Choice B is incorrect as it describes a malignant tumor, not a benign one. Choice C is incorrect as it describes thyroiditis, not a toxic adenoma.

Correct Answer: B

Rationale: The correct answer is B: ductless. Endocrine glands release hormones directly into the bloodstream without the use of ducts. This allows hormones to reach target organs throughout the body. Choice A (vascular) is incorrect because it refers to the presence of blood vessels, which is common in all glands, not just endocrine glands. Choice C (square) is irrelevant as the shape of glands does not determine their function. Choice D (autonomous) is incorrect as it does not accurately describe endocrine glands; while they function independently, the term "autonomous" does not specifically apply to them.

Correct Answer: D

Rationale: The correct answer is D: second messengers. Protein hormones typically bind to cell surface receptors, activating second messenger systems to relay the signal inside the cell. This mechanism allows for rapid and amplified cellular responses. Choices A and B (cytoplasmic and nuclear receptors) are more commonly associated with steroid hormones, not protein hormones. Choice C (cyclic ribosomal adenosine phosphate) is not a known mechanism of hormone action. Thus, the correct answer is D, as second messengers are the primary mediators of protein hormone actions.

Correct Answer: A

Rationale: The correct answer is A because ADH secretion is increased during stress to retain water in the body. This response helps maintain blood pressure and prevent dehydration under stressful conditions. Choice B is incorrect because ADH secretion is actually increased during hemorrhage to conserve water. Choice C is incorrect because increased blood osmolality triggers ADH secretion to retain water. Choice D is incorrect because alcohol inhibits ADH secretion, leading to increased urine production.

Correct Answer: D

Rationale: The correct answer is D because the anterior pituitary is regulated by hypothalamic neuropeptides. The hypothalamus secretes releasing and inhibiting hormones that control the anterior pituitary's hormone release. This close interaction between the hypothalamus and the anterior pituitary is known as the hypothalamic-pituitary axis. A is incorrect because the anterior pituitary is not neural tissue, it is an endocrine gland. B is incorrect because the anterior pituitary synthesizes and secretes peptide hormones, not steroid hormones. C is incorrect because the anterior pituitary is located at the base of the brain, not above the kidney.