The hormone secreted in response to decreased plasma calcium levels is

Correct Answer: C

Rationale: Parathyroid hormone (PTH) increases plasma calcium by mobilizing bone calcium and renal reabsorption when levels drop. 'Parathyroid hormone,' is correct, per endocrinology texts like Williams, countering hypocalcemia. 'Calcitonin,' lowers calcium, opposing PTH. 'Aldosterone,' regulates sodium, not calcium directly. 'Adrenaline,' affects metabolism, not calcium. PTH's specific response to low calcium, restoring balance, makes C the precise answer, rooted in calcium homeostasis.

Correct Answer: B

Rationale: The loop of Henle extends into the renal medulla, creating a concentration gradient for urine. 'Loop of Henle,' is correct, per anatomy texts like Moore, with its descending and ascending limbs medullary. 'Proximal convoluted tubule,' and 'Distal convoluted tubule,' are cortical. 'Bowman's capsule,' is in the cortex. The loop's medullary location distinguishes B as the accurate answer.

Correct Answer: D

Rationale: Respiration rate adjusts to metabolic demands and gas levels. 'Body weight,' is correct as the exception, not directly affecting rate, per physiology (e.g., West). 'Carbon dioxide,' drives ventilation via pH. 'Oxygen,' influences in hypoxia. 'Temperature,' alters metabolism. Weight's indirect impact (e.g., obesity on mechanics) contrasts with direct triggers, making D the precise answer.

Correct Answer: A

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.

Correct Answer: B

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.