Function
The vena cava has the task of collecting blood from the periphery of the body and returning it to the heart. It is also jointly responsible for filling the right heart. The pressure in the vena cava is between 0 and 15 mmHg.
The pressure shows respiration-dependent and pulse-synchronous fluctuations, which is known as the venous pulse. This pressure can be determined and as a diagnostic measure, especially in intensive care therapy, can be important for the assessment of cardiovascular function. This central venous pressure is dependent on the blood filling the circulatory system and the pumping capacity of the heart.
It is also dependent on the suction effect of breathing, the valve-plane mechanism of the heart action, the arteriovenous pressure gradient and the pumping force of the heart. The suction effect of breathing occurs because the pressure in the thorax drops to negative pressure values during inhalation. In this way, blood is sucked in from the periphery.
At the same time, as the diaphragm is lowered during inhalation, the pressure in the abdominal cavity increases, which causes the abdominal vessels to be compressed, thus increasing the backflow to the heart. Heart valves function like valves that only allow blood to pass in one direction. In the heart, all heart valves lie in one plane.
During the action of the heart, the shortening of the muscle fibers causes this valve plane to shift, thus creating additional suction to support the venous return flow. The skeletal muscles shorten and thicken when they are activated. The thickening causes the veins in the legs to be compressed and squeezed out. Venous valves in the leg veins prevent the blood from sinking back into the legs. The vena cava itself has no venous valves.
Histological structure
I will subdivide the vein walls into layers. The layers are thinner than the walls of the arteries. Towards the vascular lumen is the intima, a single layer of specialized cells (endothelial cells).
The endothelial cell layer is closed by the Membrana elastica interna, a network of elastic fibers produced by the smooth muscle cells of the subsequent media. This is followed by the Membrana elastica externa.The last layer is the Adventitia. It consists of connective tissue and anchors a vessel in the environment. In the vena cava, the adventitia contains smooth muscle fibers arranged lengthwise. Blood vessels must also be supplied by small blood vessels (vasa vasorum), which run through the adventitia and can penetrate to the media.