We all know that the heart is the organ the pumps blood throughout the entire body. But, how does the blood circulate through the heart before it circulates through the rest of the body? In order to answer this question, we first need to know where the blood that enters the heart comes from.
Blood enters the heart either from the superior vena cava or inferior vena cava, both of which are veins that carry unoxygenated blood (CO2 containing blood). The superior vena cava contains blood that is being transported from the head, while the inferior vena cava transports blood from the rest of the body. The names of these veins do not denote the size of the veins. Instead, the names refer to where they are in relation to each other with the superior vena cava being located above the inferior vena cava.
Upon entering the heart, the blood is now in the right atrium. The blood then enters the right ventricle by passing through the tricuspid valve. This valve is located at the top of the right ventricle and is there to prevent the backflow of blood into the right atrium. If this valve is not functioning properly, it is called a heart murmur.
Next, blood is transported to lungs by pulmonary artery; which is the only artery in the human body that transports unoxygenated blood. Located in the pulmonary artery is a pulmonary semilunar valve, which prevents the backflow of blood into the right ventricle. In the lungs, gas exchange occurs and the blood is now oxygenated.
Blood is then transported back to the heart by the pulmonary vein. Conversely similar to the pulmonary artery, the pulmonary vein is the only vein in the human body that transports oxygenated blood. Located in the pulmonary vein is another pulmonary semilunar valve that prevents the backflow of blood; in this case, to the lungs.
After reentering the heart, the blood is now in the left atrium. Next, the blood enters the left ventricle by passing through the bicuspid valve. The bicuspid valve is located at the top of the left ventricle and prevents the backflow of blood into the left atrium. Like the tricuspid valve, if this valve is not functional, it is also called a heart murmur.
The blood then exits the left ventricle and the heart through the aorta and is transported to the rest of the body. The aorta has an aortic semilunar valve in order to stop the backflow of blood from the artery back to the heart.
Since the heart cannot get nutrients from the blood it pumps, it has to get nutrients another way. The heart gets blood form coronary arteries that are found on the surface of the heart. The coronary arteries are branched off from the aorta. If the coronary arteries become clogged, it can result in a heart attack. The only way to clean out the blockage is through bypass surgery.
Although the heart may only the size of your fist, it contains many small parts that work together to ensure the blood circulates properly through the heart so it can then circulate properly through the rest of the body.