The systemic circulation is also called the great circulation. It carries blood through the majority of the body. The other major circulation of the body is the pulmonary circulation, which carries blood to and from the lungs.
What is the circulatory system?
The main function of the systemic circulation is to supply oxygenated blood to organs and body tissues and to dispose of venous blood. The systemic circulation begins in the left ventricle. With the contraction of the ventricular muscles, the oxygen-rich blood is expelled through the aortic valve into the aorta. Thus, 80 milliliters of blood enter the aorta per heartbeat. The amount of blood ejected is also known as stroke volume. The aorta arises directly from the heart. With a diameter of about three centimeters and a length of about forty centimeters, it is the largest artery in the human body. Its shape resembles a walking stick. The arcuate beginning runs above the heart, after which the vessel runs downward to the pelvis. According to its shape, the aorta is divided into an ascending aorta, the aortic arch and a descending aorta. The descending aorta can in turn be divided into thoracic aorta and abdominal aorta. All other major arterial vessels branch off from the aorta. The major branches include the brachiocephalic trunk, the common carotid artery, the subclavian artery, the coeliac trunk, the superior mesenteric artery, the inferior mesenteric artery, and the common iliac arteries. These large arteries divide into smaller and smaller arteries. The arteries then branch into arterioles. Arterioles are small arteries. They are the finest blood vessels still visible to the naked eye. The arterioles are followed by the capillaries. They are only 0.5 millimeters long and have a maximum vessel diameter of 10 micrometers. They form a fine capillary network in the organs and tissues, which is supplied with blood by the arterioles. The capillaries merge into venules. In these, the deoxygenated blood from the organs and tissues collects. The venules unite to form larger veins. Some veins have intervening portal veins. The best known and most important portal vein is the portal vein of the liver (vena portae). It collects all the blood from the unpaired abdominal organs. Finally, all the veins of the body pass into the superior (superior vena cava) or inferior (inferior vena cava) vena cava. These two major veins carry venous blood back to the heart. They open into the atrium of the right heart. From there, the blood travels through the small circuit to the lungs and finally to the left atrium. Then the great circuit begins again.
Function and purpose
The main task of the systemic circulation is to supply the organs and body tissues with oxygenated blood and to dispose of venous blood. There is high pressure and high flow velocity in the large arteries. As a result, the blood is rapidly distributed throughout the body. The arterioles serve as control valves. If the blood were to flow into the small capillaries with the pressure of the large arteries, vascular and tissue damage would occur. Arterioles have very strong muscular walls. They can control blood flow by closing (vasoconstriction) or opening (vasodilation). The small capillaries serve to exchange fluids, electrolytes, vitamins, nutrients, hormones and other substances. For this function, the capillaries are equipped with a thin vascular wall. For small-molecule substances, this membrane is permeable, so that all required nutrients can reach the tissue. In some organs, the capillaries are dilated. Such sinusoids are found, for example, in the liver and spleen. The surface of the sinusoids also allows the passage of larger molecules. In the liver, for example, proteins are synthesized that must pass through the sinusoids. In the spleen, red blood cells exit. One of the purposes of the spleen is to sort out obsolete or deformed blood cells. Like the capillaries, the venules have only a very thin vascular wall. They collect venous blood from the tissues and feed it to the veins. Thus, they additionally serve to remove waste and metabolic waste products. The veins have thin but muscular walls. They also serve the body as blood reservoirs. Another important function of the body’s circulatory system is thermoregulation. The degree of blood flow to the skin is controlled via the vessels.This also regulates the heat dissipation over the body surface and ultimately the body temperature.
Diseases and ailments
Diseases in the body’s circulatory system can affect the heart or blood vessels. The most common cardiovascular disease is high blood pressure. In the long run, too high blood pressure damages the heart and blood vessels. The high pressure can cause small tears to form in the inner lining of the blood vessels. At these points, the vessel walls thicken and harden to stabilize: atherosclerosis develops. Other risk factors for the development of vascular calcification are lack of exercise, obesity, smoking, gout, diabetes mellitus or elevated cholesterol levels (hypercholesterolemia). Consequential diseases of atherosclerosis are heart attack or stroke. Peripheral arterial occlusive disease (pAVK) and renal insufficiency are also possible consequences of vascular calcification. A life-threatening disease of the circulatory system is aortic aneurysm. It is a bulging of the aorta. In the case of a pronounced aneurysm, rupture is imminent. Such a rupture is associated with a very high mortality rate. The affected patients bleed to death internally within a few minutes. Particularly insidious is that most aneurysms cause no symptoms before rupture.
