Understanding the Cardiac Cycle

The cardiac cycle involves a series of events that repeat with each heartbeat, divided into systole and diastole. Systole refers to ventricular contraction, while diastole refers to relaxation. Blood flows from high to low pressure, with valves opening and closing based on pressure gradients. The cycle starts with the SA node firing, leading to atrial contraction and ventricular filling. Ventricular contraction follows, leading to blood ejection. The cycle ends with diastole, where the ventricles relax and fill again, repeating the process.

What are the two main phases of the cardiac cycle?

• Contraction and Relaxation

• Atrial and Ventricular

• Systole and Diastole

• Depolarization and Repolarization

Which node initiates the cardiac cycle?

• Purkinje fibers

• Bundle of His

• SA node

• AV node

What event marks the beginning of systole?

• Opening of semilunar valves

• Closing of AV valves

• Atrial contraction

• Ventricular filling

During which phase do the ventricles contract without changing volume?

• Atrial contraction

• Ventricular filling

• Rapid ejection

• Isovolumetric contraction

What causes the semilunar valves to open?

• Atrial pressure exceeds ventricular pressure

• Ventricular pressure exceeds aortic/pulmonary pressure

• Aortic pressure exceeds ventricular pressure

• Ventricular pressure falls below atrial pressure

What marks the end of systole?

• Opening of AV valves

• Closing of semilunar valves

• Ventricular depolarization

• Atrial contraction

What is the first part of diastole called?

• Isovolumetric relaxation

• Ventricular ejection

• Rapid filling

• Atrial contraction

When do the AV valves open during the cardiac cycle?

• When ventricular pressure exceeds aortic pressure

• When atrial pressure exceeds ventricular pressure

• When ventricular pressure exceeds atrial pressure

• When aortic pressure exceeds ventricular pressure

What happens during ventricular filling?

• Atria contract to push blood into ventricles

• Blood is ejected from the ventricles

• Ventricles contract without changing volume

• Blood flows passively into the ventricles

What is the role of atrial contraction in ventricular filling?

• It only contributes a small fraction to ventricular filling

• It accounts for most of the ventricular filling

• It initiates the cardiac cycle

• It prevents backflow of blood