The function of the heart is to act as a blood pump for the circulatory system, providing continuous blood flow to the entire body. This circulation consists of systemic circulation to and from the corpus callosum and pulmonary circulation to and from the lungs. The blood conducts a gaseous exchange in the pulmonary circulation, giving up carbon dioxide and capturing oxygen instead in a process known as respiration. The blood is then transported to the heart and from it to the body through the systemic circulation, where oxygen is given to the tissues of the body and the blood is loaded with carbon dioxide, and this deoxygenated blood is returned to the heart again in order to pump it to the lungs to repeat the same process.[9]
The right heart collects deoxygenated blood from two large major veins, the superior vena cava and the inferior vena cava, where the blood collects in the atria continuously.[9] The superior vena cava drains blood from whatever is above the diaphragm and empties into the upper posterior part of the right atrium, while the inferior vena cava drains blood from whatever is below the diaphragm and empties into the posterior part of the right atrium below the mouth of the superior vena cava. The mouth of the coronary sinus is located just above and medial to the mouth of the inferior vena cava.[9] In addition, the coronary sinus drains deoxygenated blood from the myocardium into the right atrium. As previously mentioned, blood is collected in the right atrium, and when the right atrium contracts, blood is pumped through the tricuspid valve into the right ventricle. When the right ventricle contracts, the tricuspid valve closes and blood is pumped to the pulmonary trunk through the pulmonary valve. The pulmonary trunk divides into two pulmonary arteries, which in turn divide into ever smaller arteries in the lungs, until they branch out into the capillaries. These capillaries pass near the alveoli of the lungs where gas exchange takes place.
In the left heart, blood returns to the left atrium through the pulmonary veins, and then is pumped into the left ventricle through the mitral valve, and then through the aortic valve into the systemic circulation. The aorta is a large artery that branches into smaller arterioles, then arterioles, and finally capillaries. In the capillaries, the body’s cells take in oxygen and nutrients from the blood for metabolism, and excrete carbon dioxide and waste products of metabolism.[9] The capillary blood hereby becomes deoxygenated and travels through the venules and venules that drain into the superior and inferior vena cava on the right side of the heart.
