Complete the following sentence: Calcium homeostasis is controlled by…

Correct Answer: D

Rationale: The correct answer is D: Parathyroid hormone. Parathyroid hormone plays a crucial role in regulating calcium homeostasis by increasing calcium levels in the blood through various mechanisms. It promotes calcium release from bones, enhances calcium absorption in the intestines, and reduces calcium excretion from the kidneys. Insulin (Choice A) primarily regulates blood sugar levels, not calcium. Erythropoietin (Choice B) stimulates red blood cell production and does not directly affect calcium homeostasis. Aldosterone (Choice C) regulates sodium and potassium balance but not calcium levels. Thus, Parathyroid hormone is the correct choice for controlling calcium homeostasis.

Correct Answer: D

Rationale: The correct answer is D. Folate absorption is not Na+ dependent because it is absorbed in the small intestine through a carrier-mediated process independent of sodium. Thiamin, riboflavin, and niacin require sodium-dependent transport mechanisms for absorption in the small intestine. Thiamin is absorbed through thiamin transporters that are Na+ dependent. Riboflavin is absorbed by sodium-dependent multivitamin transporters. Niacin absorption also involves sodium-dependent transporters. Therefore, folate is the only option that is not Na+ dependent for absorption.

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.