The heart and blood vessels, which together maintain a continuous flow of blood throughout the body. The system provides tissues with oxygen and nutrients, and carries away waste products. The circulatory system consists of 2 main parts: the systemic circulation, which supplies blood to the whole body apart from the lungs; and the pulmonary circulation to the lungs. Within the systemic circulation, there is a bypass (the portal circulation), which carries nutrient-rich blood from the stomach, intestine, and other digestive organs to the liver for processing, storage, or re-entry into general circulation. In the systemic circulation, oxygen-rich blood from the pulmonary circulation is pumped under high pressure from the left ventricle of the heart into the aorta, from where it travels through arteries and smaller arterioles to all parts of the body. Within body tissues, the arterioles branch into networks of fine blood vessels called capillaries. Oxygen and other nutrients pass from the blood through the capillaries’ thin walls into body tissues; carbon dioxide and other wastes pass in the opposite direction. Deoxygenated blood is returned to the heart via venules, veins, and the venae cavae. Venous blood returns to the right atrium of the heart to enter the pulmonary circulation. It is pumped from the right ventricle through the pulmonary artery to the lungs, where carbon dioxide is exchanged for oxygen. The reoxygenated blood then returns through the pulmonary veins to the heart and re-enters the systemic circulation.
Circulatory system |
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