Multiple Choice Quiz: The Cardiac Cycle

What is the cardiac cycle, and what two main events does a single cycle encompass?

• The cardiac cycle is the rhythmic contraction of the heart, consisting of atrial systole and ventricular diastole.

• The cardiac cycle is the sequence of blood flow through the heart, consisting of oxygenation and deoxygenation.

• The cardiac cycle is the electrical activity of the heart, consisting of depolarization and repolarization.

• The cardiac cycle encompasses all events from the beginning of one heartbeat to the next, consisting of systole and diastole.

Describe the role of the sinoatrial (SA) node in initiating the cardiac cycle. What is the corresponding event on an electrocardiogram (ECG)?

• The SA node delays the electrical impulse, allowing the ventricles to fill; this is represented by the QRS complex on the ECG.

• The SA node initiates the electrical impulse, causing ventricular depolarization; this is represented by the T wave on the ECG.

• The SA node initiates the electrical impulse, causing atrial depolarization; this is represented by the QRS complex on the ECG.

• The SA node initiates the electrical impulse, causing atrial depolarization; this is represented by the P wave on the ECG.

During atrial systole, what happens to the pressure within the atria, and what is the consequence of this pressure change? Approximately what percentage of ventricular blood volume is added during this phase?

• Atrial systole decreases atrial pressure, causing 75% of blood to flow into the ventricles.

• Atrial systole increases atrial pressure, forcing 50% of blood into the ventricles.

• Atrial systole has no effect on atrial pressure and adds 10% of blood to the ventricles.

Explain the meaning of "isovolumetric" in the context of isovolumetric ventricular contraction. Which heart valves are open and closed during this phase?

• "Isovolumetric" means volume changes rapidly; atrioventricular valves are open, and semilunar valves are closed.

• "Isovolumetric" means volume changes slowly; all heart valves are open.

• "Isovolumetric" means volume remains the same; atrioventricular valves are closed, and semilunar valves are open.

• "Isovolumetric" means volume remains the same; all four heart valves are closed.

What electrical event in the ventricles is represented by the QRS complex on an ECG, and what mechanical event follows?

• The QRS complex represents atrial repolarization, followed by ventricular relaxation.

• The QRS complex represents ventricular repolarization, followed by ventricular contraction.

• The QRS complex represents atrial depolarization, followed by ventricular contraction.

• The QRS complex represents ventricular depolarization, followed by ventricular contraction.

Define stroke volume and explain how it is calculated. What are the typical values for end-diastolic volume and end-systolic volume?

• Stroke volume is the total volume of blood in the heart; calculated as end-systolic volume minus end-diastolic volume (100 ml - 50 ml = 50 ml).

• Stroke volume is the amount of blood returning to the heart; calculated as end-diastolic volume plus end-systolic volume (130 ml + 60 ml = 190 ml).

• Stroke volume is the amount of blood ejected by each ventricle; calculated as end-diastolic volume minus end-systolic volume (130 ml - 60 ml = 70 ml).

What causes the aortic valve to open, initiating the ejection phase of the cardiac cycle? Briefly describe the two sub-phases of ventricular ejection.

• The aortic valve opens when the pressure in the aorta exceeds the pressure in the left ventricle; the ejection phase includes slow ejection followed by rapid ejection.

• The aortic valve opens when the pressure in the right ventricle exceeds the pressure in the pulmonary artery; the ejection phase includes rapid ejection and reduced ejection.

• The aortic valve opens when the pressure in the left ventricle exceeds the pressure in the aorta; the ejection phase includes a rapid ejection phase and a slower ejection phase.

• The aortic valve opens when the pressure in the left atrium exceeds the pressure in the left ventricle; the ejection phase includes a slow ejection phase and a reduced ejection phase.

What electrical event is represented by the T wave on an ECG, and what mechanical event in the ventricles follows this electrical activity?

• The T wave represents atrial repolarization, and ventricular contraction follows.

• The T wave represents ventricular depolarization, and ventricular contraction follows.

• The T wave represents atrial depolarization, and ventricular relaxation follows.

• The T wave represents ventricular repolarization, and ventricular relaxation follows.

Explain what causes the first and second heart sounds ("lub" and "dub"). Which valves are involved in the generation of each sound?

• The first heart sound ("dub") is caused by the closure of the atrioventricular valves; the second heart sound ("lub") is caused by the closure of the semilunar valves.

• The first heart sound ("lub") is caused by the closure of the semilunar valves; the second heart sound ("dub") is caused by the closure of the atrioventricular valves.

During ventricular filling, are the ventricles contracting or relaxing? What causes the blood to flow into the ventricles during this phase?

• Ventricles are contracting; blood flows in due to ventricular contraction.

• Ventricles are contracting; blood flows in due to atrial contraction.

• Ventricles are relaxing; blood flows in due to atrial contraction.

• Ventricles are relaxing; blood flows passively from the atria due to the pressure gradient.