Cardiac cycle MCQ - Practice Questions with Answers

Cardiac cycle

• Cardiac cycle refers to the one cycle of contraction and relaxation of the cardiac muscles or one heartbeat.
• A heart beat consists of contraction and relaxation of atria and ventricles. 
• The phase of contraction is referred to as systole while the phase of relaxation is called diastole.
• The term joint diastole is used when both atria and ventricles are undergoing relaxation or diastole together
• During joint diastole, the blood is carried from superior and inferior vena cava into the atria and from atria to the ventricles through auriculoventricular valves
• Blood flow is then restricted from ventricle to aorta and pulmonary trunk
• The stages of cardiac cycle

1. Atrial systole- In this step, there is a wave of contraction stimulated by the SA node. As a result of this the atria contract and blood is forced into the ventricles as the bicuspid and tricuspid valves are open
2. Atrial diastole- In this stage, the atrial systole ends and atrial diastole begins
3. Beginning of ventricular systole- This step includes a wave of contraction that is stimulated by AV node. This causes the ventricles to begin contracting . The bicuspid and tricuspid valves closes leading to appearance of first heart sound called Lubb
4. Complete ventricular systole- In this step, ventricles show complete contraction and as a result of this, blood flows into the pulmonary trunk and aorta as the semilunar valve is open  
5. Beginning of ventricular diastole- In this step the ventricles begin to relax leading to closure of semilunar valve. This causes the second heart sound dub to appear
6. Complete ventricular diastole- In this stage of cardiac cycle, the pressure in the ventricles fall, the bicuspid and tricuspid valves open and blood flows from atria into the ventricles. This blood flow is facilitated because the pressure within the relaxed ventricles is lesser than that in atria and veins