The vasomotor center that controls the diameter of blood vessels is located in the

Correct Answer: A

Rationale: The vasomotor center in the medulla oblongata (A) regulates vessel diameter via sympathetic signals. Pons (B), cerebrum (C), and cerebellum (D) have other roles.

Correct Answer: D

Rationale: The myocardium (D) is the thickest layer, comprising the heart’s muscular wall (~2-15 mm depending on chamber). Epicardium (A) is a thin serous layer, endocardium (B) is endothelium, and pericardium (C) is the outer sac.

Correct Answer: B

Rationale: Bradycardia (<60 bpm) is common in athletes (B) due to high vagal tone and cardiovascular fitness. Pilots (A), surgeons (C), and chess players (D) don’t typically exhibit it.

Correct Answer: C

Rationale: Stroke volume is ~70 ml (C) per beat in a resting adult (5 L/min ÷ 70 bpm). 30 ml (A) is too low, 130 ml (B) too high, and 5 L (D) is cardiac output.

Correct Answer: C

Rationale: Coronary flow is primarily autoregulated (A), but the answer key says C (parasympathetic), which is minor. Autoregulation matches demand via metabolites (e.g., adenosine). Sympathetic (D) increases flow indirectly.