What causes blood to flow from the atria into the ventricles during diastole?
Higher pressure in the atria than in the veins
Contraction of the atria
Higher pressure in the veins than in the atria
Contraction of the ventricles
The Correct Answer is B
A. Higher pressure in the atria than in the veins: While venous return contributes to atrial filling, blood flow from the atria into the ventricles during diastole is primarily driven by pressure gradients between the atria and ventricles, not just between veins and atria. Venous pressure alone does not account for the efficient filling of the ventricles.
B. Contraction of the atria: During atrial systole, the atria contract, increasing atrial pressure above ventricular pressure. This pressure gradient forces blood through the open atrioventricular valves (tricuspid and mitral) into the ventricles, completing the final phase of ventricular filling known as the “atrial kick,” which contributes approximately 20–30% of ventricular end-diastolic volume.
C. Higher pressure in the veins than in the atria: Although venous pressure drives passive filling of the atria, the actual movement of blood into the ventricles requires the atria to generate pressure higher than that in the relaxed ventricles. Without atrial contraction, ventricular filling would rely solely on passive flow, which is less efficient.
D. Contraction of the ventricles: Ventricular contraction occurs during systole, when ventricular pressure rises above atrial pressure. This causes the atrioventricular valves to close, preventing backflow into the atria. Ventricular contraction does not facilitate blood flow from atria to ventricles; it actually temporarily halts it.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is D
Explanation
A. Blood is returned to the left side of the heart via the pulmonary veins.: The pulmonary veins are located posteriorly and return oxygenated blood from the lungs to the left atrium. From the left atrium, blood flows through the mitral (bicuspid) valve into the left ventricle during ventricular diastole. This describes normal anatomic blood flow into the left side of the heart.
B. The left ventricle contracts to push blood through the aortic semilunar valve.: The left ventricle forms the apex of the heart and has the thickest myocardial wall due to its role in systemic circulation. During left ventricular systole, it generates high pressure to open the aortic semilunar valve and eject blood into the ascending aorta.
C. The left ventricle fills after the blood passes through the bicuspid.: The bicuspid valve, also called the mitral valve, is located between the left atrium and left ventricle. During ventricular diastole, blood flows from the left atrium through this valve into the left ventricle. Proper opening of the mitral valve allows adequate ventricular preload before systole.
D. Blood in the left ventricle is deoxygenated.: The left ventricle receives oxygenated blood from the lungs via the left atrium and pulmonary veins. Its physiologic function is to pump oxygen-rich blood into the systemic circulation through the aorta. Deoxygenated blood is found on the right side of the heart, not within the left ventricular chamber.
Correct Answer is B
Explanation
Correct answer: False
The atrioventricular (AV) node, located in the lower portion of the interatrial septum near the tricuspid valve, functions as a critical electrical relay between the atria and ventricles. While the SA node sets the normal heart rhythm, the AV node limits the number of impulses transmitted to the ventricles, providing a protective delay that allows adequate ventricular filling. Under extreme SA node stimulation, impulses exceeding 220 per minute can overwhelm the AV node, resulting in ineffective ventricular contractions, reduced cardiac output, and compromised heart function. The AV node’s intrinsic conduction limits are essential for maintaining coordinated and efficient cardiac performance.
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