The function of the arteries is to carry oxygenated blood to organs and cells in the body. Because of this, arterial blood has a bright red color and flows away from the heart.
Arterial walls have three layers. The outer layer is elastic connective tissue, and the middle layer is made out of muscle. The inner lining of the artery is made up of smooth cells called the endothelium, which are similar to the cells in the heart. When the heart beats, the walls of the arteries enlarge to make room for the blood that's pumped into them. Then, the muscular layer contracts slowly to pump the blood further down the arteries to the arterioles and capillaries.
The largest artery in the body is the aorta, which connects directly to the heart. Two branches of the aorta are the coronary arteries, which both send oxygen and nourishment to the heart. The carotid arteries send blood to the sides of the head and neck. The aorta divides in the abdomen to form the iliac arteries, which then continue down into the legs. When the blood is depleted of oxygen, it's collected by veins and sent to the pulmonary arteries and lungs.