Select the correct statement about the structure or function of chemical messengers.

Correct Answer: C

Rationale: The correct answer is C: An amino acid derivative can be a hormone. This statement is correct because many hormones are derived from amino acids, such as thyroid hormones (derived from tyrosine) and epinephrine (derived from phenylalanine). Hormones can be derived from various sources, including amino acids, peptides, lipids, and even gases. Explanation of other choices: A: Prostaglandins are not biologically active peptides; they are lipid compounds derived from fatty acids. B: Modified cholesterol does not form the main structural component of peptone hormones; peptides are the main structural components of peptide hormones. D: Testosterone is a steroid hormone and not an example of a paracrine, which is a type of chemical messenger that acts on nearby cells.

Correct Answer: C

Rationale: The correct answer is C: Pituitary gland. The pituitary gland is an endocrine gland located at the base of the brain, below the hypothalamus. It secretes various hormones that regulate important functions in the body. The other choices are incorrect because: A: Adrenal gland - located on top of the kidneys, not in the brain. B: Pancreas - located in the abdomen, not in the brain. D: Parathyroid glands - located in the neck, not in the brain.

Correct Answer: D

Rationale: The correct answer is D: adrenal cortex. ACTH stimulates the adrenal cortex to produce and release its hormones, including cortisol. The anterior pituitary produces ACTH, but it does not release hormones itself. The adrenal medulla is primarily stimulated by the sympathetic nervous system, not ACTH. The kidneys are not directly stimulated by ACTH to produce and release hormones. Therefore, the adrenal cortex is the correct choice as it directly responds to ACTH stimulation.

Correct Answer: D

Rationale: The correct answer is D: adrenal gland. The adrenal gland secretes cortisol and aldosterone. Cortisol is essential for regulating metabolism, immune response, and stress. Aldosterone helps regulate blood pressure and electrolyte balance. The other choices are incorrect because the thyroid gland (A) secretes hormones like thyroid hormone and calcitonin, the parathyroid gland (B) secretes parathyroid hormone, and the pancreas (C) secretes insulin and glucagon. Only the adrenal gland (D) secretes cortisol and aldosterone, making it the correct answer.

Correct Answer: B

Rationale: The correct answer is B: pancreas; glucagon. When blood glucose levels are low, the pancreas secretes glucagon. Glucagon acts to increase blood glucose levels by stimulating the liver to release stored glucose. The adrenal cortex does not directly regulate blood glucose levels through aldosterone secretion. Insulin is secreted by the pancreas in response to high blood glucose levels to lower them, not increase them. The posterior pituitary secretes ADH to regulate water balance, not blood glucose levels.