The Human Heart

The Human Heart

The human heart has four chambers. On each side of the heart there is one atrium and one ventricle, thus referred to as the left atrium, left ventricle, right atrium and right ventricle. To ensure that blood does not flow backwards, the heart uses several valves, limited in movement by the papillary muscle. The mitral and tricuspid valves are what allow blood to flow from the atria to the ventricles but not in the other direction. The tricuspid does this for the right side and the mitral for the left. The other two valves work for the ventricles. The pulmonary valve makes sure blood continues in a forward motion through the pulmonary arteries and out of the heart. The aortic valve works for the left ventricle and also guarantees that blood stays on a forward path out of the heart. However, the blood leaving each of these places has a very different destination, to be discussed later. The final component of the heart is the septum. The septum, from the Latin "saeptum," meaning a dividing wall or enclosure, does just that; it divides the right and left sides of the heart so the blood does not mix.

As mentioned above, there are two sides of the heart; a right side and a left side. Each side has a corresponding atrium and ventricle. The right atrium gathers de-oxygenated blood from the upper body/brain and the lower body by means of the superior (upper body) and inferior (lower body) vena cava. The oxygen-poor blood then travels through the tricuspid valve to the right atrium, where it is pumped through the pulmonary arteries to the lungs. This is called pulmonary circulation. Once in the lungs, the blood undergoes a gas exchange by receiving oxygen and leaving behind carbon dioxide. Now, the oxygenated blood travels through the pulmonary veins to the left side of the heart. The blood is pumped into the left atrium which propels it into the left ventricle after it passes through the mitral valve. When the left ventricle becomes filled with oxygen rich blood, being the strongest chamber in the heart, it thrusts the blood into the aortic valve. The aorta, the largest artery, uses its strength to pump the blood through the rest of the body. This is also known as systemic circulation.

Because their job is so crucial, let's re-examine the valves. In order to keep blood flowing in one direction, the valves open and close according to pressure differences inside of the heart and with the help of the aforementioned papillary muscle. Again, the four valves of the heart are the tricuspid, mitral, pulmonary and aortic. Once the right atrium is full of blood the tricuspid valve opens allowing it to flow into the right ventricle. Once the ventricle becomes full, a pressure change closes the tricuspid valve allowing the pulmonary valve to open and the blood to flow out of the heart to the lungs. Upon returning to the heart, the blood enters the left atrium. When this chamber becomes occupied by the oxygen-rich blood, the mitral valve bursts open pouring the scarlet red blood into the left ventricle. Again, the heart senses a pressure change and the mitral valve seals as quickly as it opened. Now, the final aortic valve opens and the blood streams onward to its target, the limbs.

Now that we know