The constant pumping action of the cardiac muscles keeps our blood circulation going. Put simply, the heart pumps oxygenated blood received from the lungs to the rest of the body, and deoxygenated blood from the rest of the body to the lungs. The oxygenated and deoxygenated blood do not mix as they enter different sides of the heart (left and right respectively), fibrous wall called the interatrial septum. Let us now study the circulation of blood in greater detail.

Oxygenated blood from the lungs enters the left auricle through veins called the pulmonary veins. It then passes into the left ventricle and is pumped out of the heart through a major artery, the aorta. It flows into the smaller arteries branching out from the aorta and ultimately, into the capillaries supplying oxygenated blood to various parts of the body.

The deoxygenated blood leaving the cells after internal respiration flows back into the heart after passing through the network of capillaries and veins. It enters the right auricle through two major veins, the superior vena cava and the inferior vena cava. From here, it passes into the right ventricle, then into the lungs through the pulmonary artery, which branches into two. The carbon dioxide in the blood is released into the alveoli of the lungs, were the blood is oxygenated again and the same cycle is repeated.

The passage between the right auricle and right ventricle is guarded by the tricuspid valve, which stops blood from flowing back from the latter to the former. The bicuspid valve prevents the backflow of blood from the left ventricle to the left auricle.

Remember that blood circulation consists of the transport of not only carbon dioxide and oxygen, but also the other substances mentioned earlier.

Heartbeat and pulse

The heart pumps blood at regular intervals by the contraction of its muscles. The auricles contract first, forcing blood into the ventricles, which relax simultaneously to let in the blood. Almost immediately after, the ventricles contract wit great force to push blood into the aorta and pulmonary artery. Next, the auricles relax to let in blood from the pulmonary veins and the superior and inferior vena cava’s. This entire takes less than a second.

The contraction of the heart muscles produces a sound called the heartbeat. This is what the doctor listens to when he puts his stethoscope to your chest. The heartbeats are an average of 72 times per minute. You can count your heartbeat by feeling pulse, which is the throbbing or swelling, of your arteries each time blood is pumped into them by the left ventricle. The pulse can be felt the most easily at wrist and the throat. The pulse rate varies according to a person’s age, state of health, the amount to a person’s age, state of health, the amount of physical exercise taken, and so on.

*Try to feel your pulse placing the index and middle fingers of your right hand over the inner side of your left wrist. First count the number of beats per minute while you are at rest and note down your reading. Repeat this 5 times, noting down each reading. Then calculate your average pulse rate. Next take another count after some exercise, like jumping or running. You will notice that this reading will be higher than your average pulse rate.



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