The human circulatory is one of, if not the, most important systems in the body. It consist of such organs as the heart and lungs. However every organ and organ system in the body is nourished and kept alive through the use of the circulatory system. The main organ in the circulatory system is the heart. Basically, the heart is a pump that keeps fresh blood coursing through your body, bringing oxygen and nutrients to all your organs and cells. " The heart keeps approximately ten pints (7.43 liters) of blood constantly circulating through seventy- five- thousand miles of blood vessels"( Dunbar2). Those thousands of miles of blood vessels reach every organ in the human body. .
Once they reach the organ they deliver much needed oxygen and take away carbon dioxide and other waste products that the body cannot use. This must be done without interruption to remain healthy and sustain life. Every living cell in the body depends on oxygen for life. Any cell deprived of oxygen for more than thirty minutes will die. The cells in the brain are even more dependent on fresh oxygen. If the brain cells are deprived of oxygen for five seconds it can cause unconsciousness to occur. If the brain is deprived for more than four minutes it will die. But, where does all this oxygen come from, the lungs.
The lungs, I believe, are the second most important organ in the circulatory system, For one reason they are the only way for oxygen to be received into the body. It is in the lungs that cells absorb fresh oxygen, and where carbon dioxide is released to be expelled from the body. The transfer of these two gasses takes place in the alveoli in the lungs. "Alveoli are "small cavities" or "air sacs in the lungs" ( Marieb G-2). Blood entering the lungs through the pulmonary circulation is dark colored, low in oxygen, and high in carbon dioxide. The blood is pumped by the right side if the heart into the pulmonary arteries, which leads to the lungs.
