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Your Circulatory System
The circulatory system is an incredibly intricate, efficient, and effective transport system in your body. Its job is to move vital materials—such as water, oxygen, and nutrients—throughout the entire body. It also carries away waste materials, like carbon dioxide, to organs that will help remove them from the body. All of these materials are carried along by blood, which is constantly pumped through the body by the heart. The blood travels through thousands of miles of blood vessels while carrying out its duties.
Needless to say, without blood, we would not be able to stay alive. Blood is an integral part of the circulatory system. The circulatory system, which is also known as the cardiovascular system, consists of three major parts:
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Heart
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Blood
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Blood vessels
The most important role of the circulatory system is to provide the cells of the body with the nourishment and oxygen they need to sustain life, and also to carry away waste products and carbon dioxide. All animals, except for the most simple, primitive ones, have some type of circulatory system.
Early Knowledge of the Circulatory System
Doctors and scientists who lived and worked thousands of years ago were aware that the heart and the blood it pumps are essential to sustaining life. Egyptian anatomists living about 3,600 years ago discovered that vessels went from the heart to all parts of the body. But they didn’t know that blood passed through those vessels. Ancient Greek philosophers believed that a person’s soul was carried through their blood.
The Greek physician Hippocrates (460–377 BC), who is called the father of medicine, believed that the body was made up of four substances called “humors.” These were blood, yellow bile, phlegm (mucus), and black bile. Bile is a thick liquid secreted by the liver that aids in the dispersion and absorption of fats. The Greeks believed that if the humors were not functioning in balance, people became ill. Other Greek philosophers such as Plato (428–347 BC) and Aristotle (384–322 BC) believed that life came from a kind of spiritual fire. It was a “flame of life” that burned in the heart. Food nourished the flame, while breathing in air kept the fire under control.
An ancient Greek doctor, Galen (AD 129–216), believed that life was sustained by a mysterious substance in the air called the pneuma. After it was breathed in through the mouth, the pneuma supposedly passed through the blood vessels in the body to the heart. There it cleansed and revitalized the blood. At the same time, pneuma took away the body’s waste substances.
Galen’s theories weren’t accurate, but they were accepted as late as the sixteenth century, when Italian anatomists made substantial discoveries about how the heart pumped blood. Realdo Columbus (1516–1559) found that there is a system of blood vessels that supplies the lungs with blood, separate from the system that supplies the rest of the body. Andrea Cesalpino (1519–1603), though he did not discover exactly how the heart pumped blood, became the first to call the body’s blood transport system “circulation.”
A major breakthrough in understanding the circulatory system came in 1628 when an English doctor, William Harvey (1578–1657), discovered that blood was pumped by the heart and flows throughout the body in a circular motion through a system of vessels. While Harvey learned that blood flows in one direction only, the Italian anatomist Marcello Malpighi (1628–1694) later discovered through microscopic studies the capillaries that connect arteries and veins.
The Path of the Circulatory System
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The Circulatory System
J. Bavosi / Photo Researchers, Inc.
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The systemic circulation starts with the left side of the heart, followed by the aorta, the largest blood vessel in the body. After the blood leaves the aorta, it travels through a system of smaller arteries and finally passes into the capillaries. There are capillaries in every tissue of our body, and that’s where the exchange of nutrients, waste products, oxygen, and carbon dioxide take place. When all its oxygen supply is used up, the blood moves into the veins and travels back to the heart.
When the oxygen-depleted blood reaches the right side of the heart, it is pumped through large vessels called pulmonary arteries and sent to the lungs. This is known as pulmonary circulation. The blood then undergoes a cleansing process in the lungs. Carbon dioxide is exchanged for oxygen in a process known as oxygenation. The blood is now rich in oxygen again. It flows back to the heart through the pulmonary veins, and another cycle of the circulatory system begins.
The third component, coronary circulation, sustains the heart muscle. The coronary arteries carry blood to the capillaries of the heart muscles. This blood then returns to the coronary veins in the left side of the heart where it will follow the pulmonary circulation.
Help from Other Systems
The circulatory system does not work all by itself, in isolation. It needs help from other organs in the body. The circulatory system works in close coordination with the respiratory system. The two systems interact when the blood pumped by the heart passes through the lungs.
Another essential partner of the circulatory system is the hematologic system. This system, which includes the lymph nodes and spleen, builds blood cells in the bone marrow. To more fully understand the circulatory system, let’s learn more about blood and the heart and how they work together to keep us healthy and alive.