Question

Describe the complete cardiac cycle and include which valves are closed at which time. What makes the heart sounds?

Answer 1

Answer. The cardiac cycle is completed in three steps:

1. Auricular systole 0.1 sec
2. Ventricular systole 0.3 sec
3. Joint diastole. 0.4 sec

Total duration= 0.8 sec

Systole means contraction and diastole means relaxation.

Initially, both auricle and ventricle are in diastole which is known as joint diastole. At this stage AV valves of both right and left chambers are open. The right auricle receives blood from the vena cava and the left auricle receives blood from the lungs via pulmonary vein. Pulmonary and aortic valves too are open at this stage.

The conduction system of heart starts working, the SA node generates the impulse that passes the AV node and helps in auricular contraction. Blood goes into both the ventricles. To prevent backfliw of blood both tricuspid valve of right chamber and bicuspid valve of left chamber closes producing a sound called LUB. It is the first heart sound.

Ventricular pressure increases beyond atrial pressure as a result ventricles contract and blood flows into aorta and pulmonary artery from left and right ventricle, respectively. Bundle of His and the Purkinje fibers too helps in ventricle contraction. This leads to the closure of pulmonary and aortic valves producing the sound DUB.