The structure of the different types of blood vessels reflects their function or layers. Fluid is also brought back to the heart via the lymphatic system. The major veins drain blood from the same organs and limbs that the major arteries supply. Veins are blood vessels that bring blood back to the heart. The capillaries converge again into venules that connect to minor veins that finally connect to major veins that take blood high in carbon dioxide back to the heart. Fluid also crosses into the interstitial space from the capillaries. Capillaries are narrow-diameter tubes that can fit red blood cells through in single file and are the sites for the exchange of nutrients, waste, and oxygen with tissues at the cellular level. Capillary beds contain a large number (10 to 100) of capillaries that branch among the cells and tissues of the body. The major arteries diverge into minor arteries, and then smaller vessels called arterioles, to reach more deeply into the muscles and organs of the body.Īrterioles diverge into capillary beds. The iliac artery takes blood to the lower limbs. These major arteries include the carotid artery that takes blood to the brain, the brachial arteries that take blood to the arms, and the thoracic artery that takes blood to the thorax and then into the hepatic, renal, and gastric arteries for the liver, kidney, and stomach, respectively. The main artery is the aorta that branches into major arteries that take blood to different limbs and organs. The blood from the heart is carried through the body by a complex network of blood vessels (Figure 1). (credit: modification of work by Mariana Ruiz Villareal) Figure 1. The major human arteries and veins are shown.
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