As the blood moves closer to the heart, the veins get larger and larger. The blood travels from the capillaries into the venules, which are the smallest veins. The blood moves back to the heart through veins. The cornea of the eye is one area that has no capillaries. Skeletal muscle, the liver, and the kidney all have a large number of capillaries because their body systems need a lot of oxygen and nutrients. The number of capillaries in a body system depends on the amount of material exchange. The capillaries connect the arteries, which take blood from the heart, and the veins, which take blood to the heart. The smallest arteries are the arterioles, which move blood from the muscular arteries to the capillaries. The femoral and coronary arteries are two examples of muscular arteries. They’re made of smooth muscle, which can expand and contract as blood flows. The muscular arteries move blood from the elastic arteries through the body. They’re the only arteries that carry deoxygenated blood. Pulmonary arteries take deoxygenated blood from the right ventricle to the lungs. The aorta is the body’s most important artery. They receive blood directly from the heart and need to be elastic to accommodate the surge and contraction as blood pushes through with each heartbeat. The aorta and pulmonary arteries are the elastic arteries. They get smaller and smaller the further they are from the heart. It’s made up of smooth muscle that changes the size of the artery to regulate blood flow. The middle layer is usually the thickest. The artery walls have three layers: tunica intima (inner), tunica media (middle), and tunica externa (outer). Arteries carry blood away from the heart.
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