Gastrin secretion is stimulated by all but:

Correct Answer: C

Rationale: The correct answer is C: luminal acid. Gastrin secretion is primarily stimulated by the presence of luminal peptides and vagal discharge. Luminal acid inhibits gastrin secretion through negative feedback mechanisms. Phenylalanine does not directly stimulate gastrin secretion. In summary, luminal acid is the correct answer because it acts as an inhibitory factor for gastrin secretion, whereas the other choices are known stimulatory factors.

Correct Answer: C

Rationale: Rationale for Choice C: Plasma norepinephrine levels are generally unchanged after adrenalectomy in the adrenal medulla because norepinephrine is mainly produced by postganglionic sympathetic nerve endings rather than the adrenal medulla. Adrenalectomy removes the adrenal gland, which primarily secretes epinephrine, not norepinephrine. Therefore, plasma norepinephrine levels would not be significantly affected by adrenalectomy. Summary of other choices: A: Incorrect. Epinephrine is formed from norepinephrine, not tyrosine, through methylation and hydroxylation. B: Incorrect. The majority of cells in the adrenal medulla are epinephrine-secreting cells, not just 10%. D: Incorrect. The half-life of catecholamines in the circulation is very short, around 2 minutes, not 10 minutes.

Correct Answer: B

Rationale: Correct Answer: B (GGP) Rationale: 1. CoA, ITP, and creatine phosphate are high-energy compounds involved in various metabolic processes. 2. GGP (guanosine-5'-triphosphate) is primarily a signaling molecule, not a high-energy compound. 3. CoA is involved in acetyl group transfer, ITP in energy transfer, and creatine phosphate in ATP regeneration. 4. GGP is a nucleotide involved in signaling pathways but does not directly participate in energy transfer reactions. Summary: - CoA, ITP, and creatine phosphate are high-energy compounds involved in energy transfer. - GGP is a signaling molecule and not classified as a high-energy compound.

Correct Answer: D

Rationale: The correct answer is D: acromegaly. After body growth is completed, excess GH production can lead to acromegaly, a condition characterized by the enlargement of bones and tissues. This occurs because GH continues to stimulate bone and tissue growth. Kidney failure (A) is not directly related to excess GH production. Tetany (B) is caused by low calcium levels, not excess GH. Gigantism (C) occurs when excess GH is produced during the growth years, leading to abnormal height, not after growth is completed. Therefore, the correct answer is D as it directly correlates with the scenario provided.

Correct Answer: D

Rationale: The correct answer is D because corticosteroids are produced by the adrenal cortex, not the adrenal medulla. Cortisol is a type of corticosteroid, making choice A incorrect. Androgens are indeed produced by the adrenal cortex, making choice B correct. Calcitonin is produced by the thyroid, not the adrenal cortex, making choice C incorrect. Therefore, the only pair that is incorrect is corticosteroid and adrenal medulla.