Blood circulation is regulated by the circulatory system, and blood is distributed throughout the body by the heart. It flows from the heart into arteries that branch into smaller veins and capillaries.
Muscle contractions in the heart pump blood into the arteries, which can then reach other parts of the body through veins and capillaries, providing oxygenated blood to cells. Capillaries have thin walls that allow red blood cells to carry oxygen and nutrients to tissues in the body while removing carbon dioxide waste from the tissues. The blood is then sent back to the heart through a series of veins and arteries to be reused.