The heart is part of the larger circulatory system. It is a large muscle that pumps blood to the lungs and the body using different blood vessels. It is important to know some basic anatomy to fully understand how the system works.
Basic Terms and Anatomy
The heart is a hollow muscular organ made up of four chambers. The top two chambers are called atria, or atrium singularly. The bottom two chambers are called ventricles. Atria are smaller than the ventricles and receive blood either from the lungs or from the body. The atria then pump that blood into the ventricles. Ventricles are larger because they have to pump the blood out of the heart into farther-reaching parts of the body, so they have to be more muscular to do their job efficiently. The left ventricle is the most muscular since it has the job of pumping the blood out into the body, whereas the right side only pumps the blood out to the lungs. In between the atria and ventricles are valves that help keep blood flowing in one direction only. There are also valves between the ventricles and blood vessels. When the atria pump, that is associated with the “lub” of the "lub dub" of a heart beat. The ventricles are associated with the "dub" of the beat. So the “dub” of the heart beat is always associated with blood flowing out of the heart.
The aorta is responsible for pumping oxygenated blood out into the body. Since this vessel carries blood to the body, it is attached to the left ventricle and arches off the top middle part of the heart. After the aorta arches off of the heart it splits into smaller and smaller vessels. There are three arteries that come off of the top of the aortic arch. One is called the brachiocephalic artery and feeds the upper right side of the body and right side of the head oxygenated blood; the other two are the left common carotid artery and the left subclavian artery. The left common carotid feeds the head, and the left subclavian feeds the upper left side of the body. If we focus our attention to the aortic arch again and just follow the arch down past the heart, it becomes the descending aorta to the abdominal aorta. The abdominal aorta splits into two vessels below the level of the belly button to send blood to the right and left lower extremities. The vessels will split smaller and smaller until they are finally arterioles in the distal most extremities, and then turn into a capillary network that starts to carry blood back to the heart.
The pulmonary arteries pump blood away from the heart to the lungs. They exit so the right ventricle. The pulmonary arteries are the only arteries that carry deoxygenated blood. The pulmonary arteries startsas one artery that branches off the front middle part of the heart, in front of the aorta. Almost immediately this one vessels splits into two pulmonary arteries, one to go to the left lung and one to go the the right lung. The pulmonary arteries rapidly become smaller and smaller until they turn into pulmonary capillaries. At the level of the capillaries, carbon dioxide is release and oxygen is attached to the blood cells. The capillary network then turns into pulmonary veins and starts to return to the heart.