Which one of the following statements is false about the trachea?

Correct Answer: B

Rationale: The trachea's false statement is 'it is covered by epiglottis.' The epiglottis, a laryngeal flap, covers the glottis during swallowing to prevent food entry, not the trachea itself it sits above. The trachea has C-shaped cartilage rings for structural support, keeping it open, true. It splits into right and left bronchi, not lungs directly, but this is anatomically accurate enough. 'None' is incorrect one is false. The trachea conducts air to the bronchi, lined with cilia and mucus, and its independence from epiglottal coverage ensures unobstructed airflow, a key anatomical fact for airway management and respiratory function.

Correct Answer: D

Rationale: Blood exits the left ventricle through the aortic semilunar valve, opening during systole to release oxygenated blood into the aorta, closing to prevent backflow. The right atrium receives deoxygenated blood, unrelated. The interventricular septum divides ventricles, not a passage. The bicuspid (mitral) valve admits blood into the ventricle, not out. This valve's half-moon shape optimizes ejection, a critical step in systemic circulation, essential in understanding cardiac output and conditions like aortic stenosis narrowing this exit.

Correct Answer: B

Rationale: Cardiac muscle fibers depolarize longer than skeletal muscle due to a prolonged plateau phase in their action potential, driven by calcium influx through L-type channels, lasting ~200-300 ms versus skeletal's ~2-5 ms. This extended depolarization ensures sustained contraction, preventing tetanus and allowing complete ventricular ejection per beat. Skeletal muscle's brief depolarization suits rapid, repeated motions. 'Same' ignores this distinction; cardiac's unique refractory period matches its continuous duty. This longer phase, key to heart rhythm, is critical in ECG interpretation and antiarrhythmic drug effects targeting calcium channels.

Correct Answer: C

Rationale: Cardiac output (CO) is the blood volume ejected from either ventricle left into the aorta (systemic), right into the pulmonary trunk (lungs) per minute, ~5 L total. 'Left, aorta' or 'right, pulmonary' alone is half; 'right, aorta' is wrong. This dual definition reflects parallel circuits, key in measuring heart efficiency, critical in failure where CO drops, a broad metric in physiology.

Correct Answer: C

Rationale: The myocardium, the heart wall's thickest layer, is cardiac muscle driving contraction thickest in the left ventricle (~1-1.5 cm) for systemic pressure. Epicardium and endocardium are thin connective layers; pericardium is the sac, not wall. This muscle bulk powers pumping, key in hypertrophy or infarction where it's affected, a core structural feature in cardiac function.