The pacemaker potential of the Sino-Atrial node is due to influx of

Correct Answer: B

Rationale: The SA node's pacemaker potential results from calcium influx via T-type channels, depolarizing cells. 'Calcium,' is correct, per cardiac physiology (e.g., Opie). 'Sodium,' contributes later in action potentials. 'Potassium,' hyperpolarizes. 'Magnesium,' is minor. Calcium's role in phase 4 depolarization makes B the precise answer.

Correct Answer: B

Rationale: Oogenesis is the formation of ova (eggs) in the ovaries, from oogonia to mature oocytes. 'Oogenesis,' is correct, per reproductive physiology (e.g., Tortora). 'Spermatogenesis,' is sperm formation. 'Ovulation,' is egg release. 'Fertilization,' is conception. Oogenesis' full developmental process makes B the accurate answer, specific to female gametes.

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.