CBSE Class 10 Answered

The Heartbeat

The heartbeat is made up of systole and diastole, which are the two stages of a heartbeat                            Systole: Stage when the ventricles of heart are contracting resulting in blood being pumped out to the lungs and the rest of the body.Diastole: Stage when the ventricles of the heart are relaxed and not contracting. During this stage, the atria are filled with blood and pump blood into the ventricles.

• Thick, muscular walls of both ventricles contract.
• Pressure rises in both ventricles, causing the bicuspid and tricuspid valves to close. Therefore, blood is forced up the aorta and the pulmonary artery.
• The atria relax during this time. The left atrium receives blood from the pulmonary vein, and the right atrium from the vena cava.

• Thick, muscular walls of both ventricles relax.
• Pressure in both ventricles falls low enough for bicuspid valves to open.
• The atria contract, and blood is forced into the ventricles, expanding them.
• The blood pressure in the aorta is decreased, therefore the semi-lunar valves close.

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