The blood circulatory system of vertebrates consists of

The blood circulatory system of vertebrates, including humans, consists of four main components: the heart, arteries, capillaries, and veins. The heart pumps blood, which is rich in oxygen and nutrients, to the rest of the body through a large artery called the aorta. The arteries branch off into smaller vessels and eventually into tiny capillaries. Capillaries are the smallest blood vessels and are responsible for delivering oxygen and nutrients to cells while removing waste products. After passing through the capillaries, the blood then flows into the veins, which gradually increase in size as they merge together to form larger vessels that eventually lead back to the heart. The largest veins in the body are the vena cava, which bring blood back to the heart from the body's lower and upper halves. This continuous loop of blood flow enables the body to receive the necessary oxygen and nutrients it needs to function properly, while also removing waste products like carbon dioxide.