At the beginning of the cardiac cycle, which of the following occurs?
The atria and ventricles are in diastole, and the atrioventricular valves are open.
The atria are in systole, the ventricles are in diastole, and the semilunar valves are open.
The atria and ventricles are in systole, and all valves are open.
The atria and ventricles are in diastole, and the semilunar valves are open.
The Correct Answer is A
A. The atria and ventricles are in diastole, and the atrioventricular valves are open: At the beginning of the cardiac cycle, both the atria and ventricles are relaxed (diastole). The atrioventricular (tricuspid and mitral) valves are open due to higher atrial pressure compared to ventricular pressure, allowing passive ventricular filling. This phase establishes the end-diastolic volume and prepares the ventricles for subsequent contraction.
B. The atria are in systole, the ventricles are in diastole, and the semilunar valves are open: During atrial systole, the atria contract to complete ventricular filling, but the semilunar valves remain closed because ventricular pressure has not yet exceeded the pressure in the aorta or pulmonary trunk.
C. The atria and ventricles are in systole, and all valves are open: Both chambers are never in systole simultaneously. If both contracted at once, it would impair filling and ejection, and physiologically, the valves are not all open at the same time.
D. The atria and ventricles are in diastole, and the semilunar valves are open: Semilunar valves (aortic and pulmonary) open only when ventricular pressure exceeds arterial pressure during ventricular systole. At the start of the cycle, ventricles are relaxed, so the semilunar valves remain closed.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is C
Explanation
A. Contractile force increases to compensate for the reduced cardiac output: In early compensatory phases, the heart may attempt to increase contractility via sympathetic stimulation, but in true heart failure, the myocardium is unable to generate sufficient force due to structural or functional impairment.
B. Contractile force increases, leading to an increased end systolic volume: Increased contractility would reduce, not increase, end-systolic volume because more blood is ejected per beat. In heart failure, contractile weakness leads to higher end-systolic volumes, reflecting incomplete emptying of the ventricles.
C. Contractile force is diminished due to damaged cardiomyocytes or cardiomyopathies: Heart failure results from conditions such as myocardial infarction, chronic hypertension, or dilated cardiomyopathy that impair cardiomyocyte function. This reduces the strength of ventricular contraction, decreasing stroke volume and overall cardiac output.
D. Contractile force is not affected in heart failure: Contractile force is significantly affected in heart failure. The weakened myocardium cannot generate sufficient pressure to maintain normal stroke volume, making this statement inaccurate.
E. Contractile force remains the same, but the heart becomes larger: While ventricular dilation can occur in chronic heart failure as a compensatory mechanism (eccentric hypertrophy), the contractile force per myocyte is reduced. Increased chamber size alone does not preserve effective contraction.
Correct Answer is {"dropdown-group-1":"B"}
Explanation
A. Inotropes: Inotropes, such as digoxin or dobutamine, increase the contractile force of the heart to improve cardiac output. They do not directly remove excess fluid or reduce blood volume.
B. Diuretics: Diuretics promote the excretion of sodium and water by the kidneys, reducing intravascular volume and venous pressure. This alleviates symptoms of fluid overload, such as pulmonary edema and peripheral edema, and decreases the workload on the failing heart, making them a cornerstone in symptomatic management of heart failure.
C. ACE inhibitors: Angiotensin-converting enzyme inhibitors lower afterload and inhibit RAAS, reducing blood pressure and preventing cardiac remodeling. While they indirectly reduce fluid retention by decreasing aldosterone levels, they are not the primary agents for rapid fluid removal.
D. Beta blockers: Beta blockers decrease sympathetic stimulation, heart rate, and myocardial oxygen demand. They improve long-term cardiac function but do not directly increase sodium or water excretion.
E. ARBs: Angiotensin II receptor blockers inhibit RAAS-mediated vasoconstriction and sodium retention, reducing afterload and preventing remodeling. Similar to ACE inhibitors, they have a modest effect on fluid retention but are not the main therapy for removing excess fluid.
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