Imagine that you are living in the year 1535, and that you don't feel well. You have had some problems with fatigue, feeling a little more tired than usual when you walked to the market and back. You tell this to your physician, and he sends you to another physician down the street, telling you there may be some problem with your circulation. When you get to the new physician, he tells you to take off your shirt and lie down on the bench. After a quick look in your mouth, he says your vital blood is probably O.K. But he's concerned that maybe your nutritive blood is not being made fast enough. Then he starts to feel around on your abdomen. He mentions that your liver is slightly enlarged and suggests that maybe you have not been eating enough green leafy vegetables or protein. Wait a minute! You have come in with problems with your circulation, and this guy is talking about your liver and the type of foods you have been eating! What is going on here? Where did this fellow learn to practice medicine anyway?

Confusion over the nature of the heart, the blood, and the role of the blood in the body had existed for centuries. Pliny the Elder, a Roman writer who lived from AD 23-

No discussion of the circulatory system would be complete without mentioning some of the problems that can occur. Several problems can occur with the valves of the heart. Valvular stenosis is the result of diseases such as rheumatic fever, which causes the opening through the valve to become so narrow that blood can flow through only with difficulty. The result can be blood damming up behind the valve. Valvular regurgitation occurs when the valves become so worn that they cannot close completely, and blood flows back into the atria or the ventricles. If the blood can flow backward, the efficiency of the cardiac stroke is drastically reduced.

Tiger, Steven. "HEART DISEASE", Julian Messner.

The coronary arteries are also subject to problems. Atherosclerosis is a degenerative disease that results in narrowing of the coronary arteries. This is caused by fatty deposits, most notably cholesterol, on the interior walls of the coronary arteries. When the walls become narrowed or occluded, they reduce the blood flow to the heart muscle. If the artery remains open to some degree, the reduced blood flow is noticed when the heart is under stress during periods of rapid heartbeat. The resulting pain is called angina. When the artery is completely closed or occluded, a section of the heart muscle can no longer get oxygenated blood, and begins to die. This is called a heart attack. Only quickly restoring the blood flow can reduce the amount of heart muscle that will die. At times, the walls of the systemic arteries become weakened. When this occurs, the wall may balloon outward, much like a weak spot in the radiator hose. This is called an aneurysm, and is an extremely dangerous condition. Like a radiator hose under pressure, the wall can rupture. Blood can then spill out of the circulatory system into the body cavity. If an aneurysm ruptures in the aorta, death is almost certain.

There are three types of vessels - arteries, veins, and capillaries. Arteries, veins, and capillaries are not anatomically the same. They are not just tubes through which the blood flows. Both arteries and veins have layers of smooth muscle surrounding them. Arteries have a much thicker layer, and many more elastic fibers as well. The largest artery, the aorta leaving the heart, also has cardiac muscle fibers in its walls for the first few inches of its length immediately leaving the heart. Arteries have to expand to accept the blood being forced into them from the heart, and then squeeze this blood on to the veins when the heart relaxes. Arteries have the property of elasticity, meaning that they can expand to accept a volume of blood, then contract and squeeze back to their original size after the pressure is released. A good way to think of them is like a balloon. When you blow into the balloon, it inflates to hold the air. When you release the opening, the balloon squeezes the air back out. It is the elasticity of the arteries that maintains the pressure on the blood when the heart relaxes, and keeps it flowing forward. if the arteries did not have this property, your blood pressure would be more like 120/0, instead of the 120/80 that is more normal. Arteries branch into arterioles as they get smaller. Arterioles eventually become capillaries, which are very thin and branching.

Since the advent of modern medical research, physicians have made quantum leaps in their understanding of the heart and in ways to treat cardiovascular disorders. When we hear of breakthroughs in cardiac medicine, we often think of radical treatments such as heart transplants or artificial hearts. The first heart transplant took place in 1967. It was performed by the South African surgeon Dr. Christiaan Barnard. The patient lived just 18 days. The first U.S. transplant took place in 1968. The rate of transplants increased in the 1970's, but most patients died within a year. The drugs given to fight rejection of the heart also lowered the body's resistance to infections. It was th

Some common words found in the essay are:
Systems Remember, Anatomy Heart, Stained Cross, Supply Heart, DeVries Due, King Charles, Bed Capillaries, Vessel Anatomy, Galen Greek, Blood Animals, blood flow, cardiac muscle, circulatory system, blood heart, oxygenated blood, heart muscle, arteries veins, smooth muscle, blood vessels, organs body, heart circulatory system, blood flow heart, arteries veins capillaries, blood flow backward, ventricles purkinje fibers,
Approximate Word count = 6235
Approximate Pages = 25 (250 words per page double spaced)