Question

Describe the events in cardiac cycle. Explain “double circulation”.

Answer 1

Cardiac cycle

• The cardiac cycle comprises all of the physiological events associated with a single heartbeat, including electrical events, mechanical events (pressures and volumes), and heart sounds.
• The atria and ventricles alternately contract in each cardiac cycle. The pressures in the chambers change greatly over the course of the cardiac cycle.
• The cardiac cycle is essentially split into two phases, systole (the contraction phase) and diastole (the relaxation phase). Each of these is then further divided into an atrial and ventricular component.

Atrial systole

• Atrial systole: lasts about 0.1 seconds - both atria contract and force the blood from the atria into the ventricles.

Ventricular systole

• Ventricular systole: lasts about 0.3 seconds - both ventricles contract, blood is forced to the lungs via the pulmonary trunk, and the rest of the body via the aorta.

Atrial diastole

• Atrial diastole: lasting about 0.7 seconds - relaxation of the atria, during which the atria fill with blood from the large veins (the vena cava).

Ventricular diastole

• Ventricular diastole: lasts about 0.5 seconds - begins before atrial systole, allowing the ventricles to fill passively with blood from the atria.

Double circulation :

• The human circulatory system has three key components: blood vessels, blood and the heart. It is called a double circulatory system because blood passes through the heart twice per circuit.
• The right ventricle sends deoxygenated blood to the lungs where it becomes oxygenated and returns back to the heart.
• The left ventricle sends the newly oxygenated blood around the body. By the time this blood returns to the heart, it has returned to a deoxygenated state.