Describe Blood Circulation In Human Body
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The first phase is called systole (pronounced: SISS-tuh-lee). This is when the ventricles contract and pump blood into the aorta and pulmonary artery. During systole, the atrioventricular valves close, creating the first sound (the lub) of a heartbeat. When the atrioventricular valves close, it keeps the blood from going back up into the atria. During this time, the aortic and pulmonary valves are open to allow blood into the aorta and pulmonary artery. When the ventricles finish contracting, the aortic and pulmonary valves close to prevent blood from flowing back into the ventricles. These valves closing is what creates the second sound (the dub) of a heartbeat.
The second phase is called diastole (pronounced: die-AS-tuh-lee). This is when the atrioventricular valves open and the ventricles relax. This allows the ventricles to fill with blood from the atria, and get ready for the next heartbeat.