The membrane that surrounds and protects the heart is called the

Correct Answer: A

Rationale: The pericardium, a double-layered sac, surrounds and protects the heart, with a fibrous outer layer anchoring it and a serous inner layer reducing friction via pericardial fluid. The pleura encase the lungs, not the heart. The myocardium is the heart's muscle layer, not a membrane. The mediastinum is the thoracic region, not a protective sac. This pericardial shield prevents overexpansion and infection, essential for heart function, a fundamental concept in cardiac anatomy, relevant in conditions like pericarditis where inflammation disrupts this protection.

Correct Answer: A

Rationale: Cardiac output (CO) is the volume of blood the left ventricle ejects into the aorta per minute, typically 5-6 liters at rest, calculated as stroke volume (blood per beat) times heart rate. 'Cardiac input' isn't a standard term venous return approximates it. Stroke volume is per beat (~70 mL), not minute. Heart rate is beats per minute, not volume. CO measures heart efficiency, key in assessing circulation and diagnosing failure where output drops, a vital metric in cardiovascular physiology and clinical monitoring.

Correct Answer: D

Rationale: Cardiac reserve is the difference between maximum cardiac output (e.g., during exercise, ~20 L/min) and resting CO (~5 L/min), reflecting the heart's capacity to increase pumping. Stroke volume is per beat. Peripheral resistance is vascular opposition, not output. Afterload is arterial pressure resisted. Reserve, boosted by rate and contractility, gauges heart health, key in fitness and failure where it diminishes, a vital performance indicator.

Correct Answer: C

Rationale: The myocardium is the heart wall's muscular layer, cardiac muscle with intercalated discs for synchronized contraction, pumping blood. Epicardium (outer) and endocardium (inner) are connective; pericardium is the external sac. This layer's thickness and strength, especially left-sided, drive heart action, key in physiology and failure where muscle weakens, a definitive cardiac component.

Correct Answer: A

Rationale: The trachea (A) is not in the respiratory zone, per the key it's a conducting zone organ. Small bronchioles (B), alveolar ducts (C), and alveoli (D) form the respiratory zone, enabling gas exchange (e.g., 5-6 L/min air). The trachea conducts air (C-shaped cartilage), not exchanging gases. Respiratory zone structures (terminal bronchioles onward) have thin walls (0.5 μm) for O₂/CO₂ diffusion, per anatomy. The trachea's role airway patency (15-20 cm long) contrasts with B's transition, C's channeling, and D's 300 million exchange sites, excluding A from the gas-exchange zone.