The Human Heart
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An Image of the Human Heart!
The Hearts Aortic Valves!
 The heart is one of the most important of the bodies organs. The heart pumps the blood that carries all the vital materials which help our bodies function and removes the waste products. For example, the brain requires oxygen and glucose. Muscles need oxygen, glucose, amino acids, and the proper ratio of sodium, calcium and potassium salts to contract normally. If the heart ever ceases to pump blood the body begins to shut down and after a very short period of time will die.
The heart is a muscle (about the size of your fist). Like any other muscle in the body, the heart contracts and expands, it is considered to be an involuntary muscle. Unlike skeletal muscles, however, the heart works on the All -or-Nothing Law: This means, each time the heart contracts it does so with all its force. In skeletal muscles, the principle of gradation is present. The pumping of the heart is called the Cardiac Cycle, this occurs 60 to 100 times per minute in the adult. What this means is each cycle lasts about eight-tenths of a second, during each cycle, the heart rests for about four-tenths of a second.
 The walls of the heart are made up of three layers, the cavity is divided into four parts. There are two upper chambers, called the right and left atria, and two lower chambers, called the right and left ventricles. The Right Atrium, receives blood from the upper and lower body through the superior vena cava and the inferior vena cava, and from the heart muscle itself through the coronary sinus. The right atrium is the larger of the two atria but the atrium has thin walls. The right atrium opens into the right ventricle through the right atrioventicular valve (tricuspid valve), this allows the blood to flow from the atria into the ventricle, but not in the reverse direction. The right ventricle pumps the blood to the lungs. This is where the blood receives it's oxygen. The left atrium receives blood from the lungs via the four pulmonary veins. Smaller than the right atrium, but has thicker walls. The valve between the left atrium and the left ventricle, the left atrioventicular valve (bicuspid valve), is smaller than the tricuspid. It opens into the left ventricle and functions as a one way valve. The left ventricle pumps the blood throughout the body. It is the Aorta, the largest artery in the body, that originates from the left ventricle.
The Heart works as a pump moving blood throughout the body. Blood that has already been to the cells and has given up its nutrients to them, is drawn from the body by the right half of the heart, it is then delivered to the lungs to be reoxygenated. Blood that has been reoxygenated by the lungs is drawn into the left side of the heart and then passed into the blood stream. It is the atria that draws the blood from the lungs and body, and the ventricles that pumps the blood to the lungs and body. The output of each ventricle per beat is about 70 ml, or about 2 tablespoons. In a well conditioned athlete, this amount may double. With the average heart rate of 60 to 100 beats per minute, the heart pumps about 5 liters of blood per ventricle, or about 10 liters total per minute. This is known as cardiac output. In a well conditioned athlete, the total cardiac output is about 20 liters. If we multiply the normal, non-athlete output by the average age of 70 years, we would see that the cardiac output of the average human heart would be about 1 million liters, over a life-time!
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