aorta (āôrˈtə) [key], primary artery of the circulatory system in mammals, delivering oxygenated blood to all other arteries except those of the lungs. The human aorta, c.1 in. (2.54 cm) in diameter, originates at the left ventricle of the heart. After supplying the coronary arteries that nourish the heart itself, the aorta extends slightly toward the neck to feed branches serving the head and arms. It then arches down toward the waist, directing blood into the arterial system of the chest. Entering the abdomen through the aortic hiatus, an opening in the diaphragm, the aorta branches off to supply the stomach, kidneys, intestines, gonads, and other organs through extensive arterial networks. It finally divides into the two iliac arteries carrying blood to the legs. The elasticity of the aorta wall permits it to pulse in rhythm with the heartbeat, thus helping to propel blood through the body.