Arteries are thick-walled, flexible, and muscular.
The blood carried by most arteries is bright red because it has picked up oxygen while passing through the lungs. The blood that flows through the pulmonary arteries connecting the right side of the heart with the lungs has not yet picked up oxygen, so this blood has a dark bluish color. Blood flow is due to contraction of the heart muscle assisted by artery muscle contraction. The largest artery is the aorta, which stems directly from the heart. Two small branches of the aorta, the coronary arteries, supply the blood that nourishes the heart muscle itself.