The aorta stretches with every heartbeat to keep blood flowing between beats
Every time the heart squeezes, the body's largest artery balloons outward, then gently recoils while the heart refills. That elastic bounce, known as the Windkessel effect, smooths the heart's jerky output into steadier flow. Nearly every organ depends on it: apart from the lungs' gas-exchange zone, the whole body draws blood from the aorta.
The aorta leaves the left ventricle through the aortic valve, climbs upward, makes a hairpin turn called the aortic arch, and then runs down through the chest and abdomen. There it splits into the two common iliac arteries that feed the pelvis and legs. Anatomists label its stretches either by body compartment, thoracic above the diaphragm and abdominal below, or by direction: ascending, arch, descending.
Each segment has its territory. Right at the root, small pockets behind the valve cusps give rise to the two coronary arteries that feed the heart muscle itself. The arch sends out three big branches that supply the head, neck and arms, and it stays tethered to the pulmonary trunk by a ligament left over from the fetal circulation. Sensors in the arch report blood pressure, acidity and carbon dioxide to the brainstem.
Its wall is built for bounce. Layers of elastic fibres and smooth muscle wrap concentrically in the middle coat, and the elastic matrix governs its mechanical behaviour; the muscle does little to change the vessel's diameter, instead stiffening the wall when it contracts. The outer layers even have their own mesh of tiny feeding vessels. Each heartbeat launches a pressure wave down the artery that echoes back from branch points, producing a small notch in the aortic pressure trace. With age the aorta stiffens, the wave travels faster and its reflection arrives before the valve closes, pushing blood pressure up, which is why pulse wave velocity is used as an independent indicator of hypertension.
The layout is ancient. All amniotes share a broadly similar plan. Fish instead have two aortas: a ventral one carrying oxygen-poor blood from the heart to the gills, and a dorsal one sending oxygenated blood onward to the body. The ventral vessel survives in land animals as part of the ascending aorta, and the dorsal one as the descending aorta.
Source: Aorta
