Multiple Choice
What is the cardiac output of a person with a heart rate of 60 beats per minute (bpm) and a stroke volume of 90 mL?
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18. The Heart
Cardiac Cycle
Multiple Choice
Which of the following correctly lists the phases of the cardiac cycle in order, starting immediately after ventricular filling?
A
Atrial systole → isovolumetric contraction → ventricular ejection → isovolumetric relaxation
B
Isovolumetric relaxation → isovolumetric contraction → ventricular ejection → atrial systole
C
Isovolumetric contraction → ventricular ejection → isovolumetric relaxation → atrial systole
D
Ventricular ejection → isovolumetric contraction → isovolumetric relaxation → atrial systole
Verified step by step guidance1
Step 1: Understand the cardiac cycle phases. The cardiac cycle consists of sequential phases that describe the mechanical events of the heart during one heartbeat. These phases include ventricular filling, atrial systole, isovolumetric contraction, ventricular ejection, isovolumetric relaxation, and diastole.
Step 2: Identify the starting point. The problem specifies starting immediately after ventricular filling, which means the next phase is atrial systole. Atrial systole involves the contraction of the atria to push additional blood into the ventricles.
Step 3: Follow the sequence of events. After atrial systole, the ventricles begin to contract without ejecting blood yet, leading to isovolumetric contraction. This phase is characterized by a rise in ventricular pressure while all heart valves remain closed.
Step 4: Continue to ventricular ejection. Once the pressure in the ventricles exceeds the pressure in the arteries, the semilunar valves open, and blood is ejected from the ventricles into the pulmonary artery and aorta.
Step 5: Conclude with isovolumetric relaxation. After ventricular ejection, the ventricles relax, and the pressure drops. The semilunar valves close, and all valves remain closed briefly before the cycle repeats with atrial systole.
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