After birth, the ductus arteriosus develops into the:

Correct Answer: B

Rationale: After birth, the ductus arteriosus, which shunts blood from the pulmonary artery to the aorta in the fetus, closes and becomes the ligamentum arteriosum, a fibrous remnant. The fossa ovalis is the remnant of the foramen ovale, and the other options relate to different fetal structures.

Correct Answer: B

Rationale: Arteriovenous shunts (or thoroughfare channels) are metarterioles connecting arterioles to venules, bypassing capillaries to regulate blood flow (e.g., in thermoregulation or under low metabolic demand).

Correct Answer: A

Rationale: Postoperative elevation in pulse and BP is typically due to the sympathetic nervous system’s response to stress (e.g., surgery), releasing catecholamines like epinephrine, increasing heart rate and vasoconstriction. The parasympathetic system slows heart rate, infection would take longer to manifest, and pain medications often lower BP.

Correct Answer: C

Rationale: Serum albumin, the most abundant plasma protein, maintains colloidal osmotic pressure (about 25 mmHg), keeping fluid in the bloodstream. Antibodies are from globulins, fibrinogen is a separate protein, and waste removal is primarily a kidney function.

Correct Answer: C

Rationale: Erythropoietin (EPO) production by the kidneys is triggered by hypoxia (e.g., hemorrhage, poor heart pumping, low oxygen). Epinephrine increases heart rate but doesn’t directly stimulate EPO.