How Your Circulatory System Works

Blood Circulation, Illustration
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The circulatory system, also known as the cardiovascular system, is a simple loop which starts, and ends, with your heart. It is a closed system, meaning blood does not enter or leave the system during its journey from your heart to your body and back again. In such a system, a continuous flow of the same liquid can be pumped through the loop again and again.

Blood is circulated throughout your body via your arterial system—arteries, arterioles, and capillaries—​​and returned to your heart via the venous system—veins and venules. Your blood is vital to your well-being and circulates nutrients including electrolytes, oxygen, carbon dioxide and amino acids throughout your body. Your heart is responsible for the majority of the circulatory system's function and is where the process begins.

Circulation Begins in Your Heart

The circulatory system begins in your right atrium, the upper right-hand chamber of your heart. Blood moves from the right side of your heart through your lungs to get rid of carbon dioxide and pick up oxygen, and then returns to the left side of your heart, ending up in the left ventricle. The left ventricle is the strongest part of the heart, since it must pump blood out to the rest of the body.

When it comes to circulating blood throughout your body, the left ventricle is the most important chamber in the heart. The left ventricle is the largest of the four chambers and is responsible for generating the force necessary to propel your blood out of your aorta, the first artery your blood enters as it leaves your heart.

From Your Aorta to Your Capillaries

Your blood travels from your aorta through a series of smaller blood vessels until it reaches your capillaries. Before reaching your capillaries, however, blood must travel through the arterioles, where its speed and pressure are constantly adjusted as different segments of the arterioles change diameter in response to pressure and chemical sensors positioned nearby. These sensors adjust blood flow via the arterioles in response to changing conditions in your body.

Because of arteriole action, by the time your blood reaches your capillaries, it is no longer traveling in a pulsing fashion. Blood flows continuously through the capillaries, it does not "squirt" and "pause" as your heart beats. This continuous flow is necessary because there is a constant exchange of oxygen and nutrients happening in the capillary walls. No cell in the body is far from a capillary.

Back to Your Heart and All Over Again

As blood travels through the capillaries, its supply of oxygen is reduced and has picked up waste products as well. From the capillaries, blood enters the venules, the veins, and then travels back to the heart to be refreshed and sent out once again.

In conclusion, your heart works like a pump which provides nutrients to every organ, tissue, and cell throughout your body. In turn, your cells dump waste products, like carbon dioxide, back into your blood to be returned to your heart.

By Craig O. Weber, MD
Craig O. Weber, MD, is a board-certified occupational specialist who has practiced for over 36 years.