What is the primary consideration when preparing to administer thrombolytic therapy to a patient who is experiencing an acute myocardial infarction (MI)?

Correct Answer: D

Rationale: Thrombolytic therapy effectiveness in acute MI depends on time since symptom onset (ideally within 6-12 hours), as it dissolves clots to restore blood flow. History (A), aspirin sensitivity (B), and MI specifics (C) are secondary to this time-sensitive factor.

Correct Answer: D

Rationale: The sinoatrial (SA) node, located in the right atrium near the superior vena cava, is known as the heart’s natural pacemaker. It initiates each heartbeat by generating electrical impulses that trigger atrial contraction. The atria (Choice A) contain the SA node but are too broad a location, the ventricles (Choice B) do not house the pacemaker, and the atrioventricular (AV) node (Choice C) relays impulses from the SA node but does not initiate them. Choice D is the precise and correct answer.

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: D

Rationale: Venous valves prevent backflow, and the skeletal-muscle pump (contractions of skeletal muscles) aids venous return by compressing veins. Skeletal-muscle groups contribute to this pump. Venous pressure alone is low (near 0 mmHg at the venae cavae) and insufficient without these mechanisms.

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).