The circulatory system moves blood around the body. The main components of this system are:
- The heart—a muscular pump that has four chambers and is about the size of its owner’s clenched fist. There is a left and a right atrium, and a left and a right ventricle. The two atria pump blood into the two ventricles, which are larger and more powerful than the atria. The left ventricle is more powerful than the right ventricle, as it needs to pump blood all the way around the body.
- Circulation of blood—is caused by the mechanical action of the heart. The heart’s right side pumps blood to the lungs, where oxygen is absorbed into the blood and carbon dioxide is released. Blood, rich with oxygen, is returned from the lungs to the left side of the heart. It is then pumped out of the heart via the aorta. The aorta then divides into many smaller arteries to supply blood and oxygen to organs, muscles and all other tissues.
- Arteries—carry blood from the heart at high pressure, so their walls are strong, muscular and elastic. The blood in the arteries is a bright red colour, due to its oxygen content; if an artery is cut, blood spurts out at the rate of the heartbeat. Serious blood loss can occur quite rapidly from a cut artery, because of the high blood pressure. Arterial bleeding is serious and must be controlled as soon as possible.
- Veins—carry blood back to the right side of the heart from the organs and muscles of the body after oxygen has been used. The blood in veins is dark red and moves at low pressure, and it is kept flowing in one direction by one-way valves. Veins are thin-walled. Many are near the surface of the skin and are easily seen as blue lines on the feet, hands and forearms.
- Capillaries—the tiny vessels that link the ends of the smallest arteries with the smallest of the veins. Each artery divides into an enormous number of these tiny vessels, which form a network that is in close contact with the cells of the body. The capillaries allow oxygen and nutrients to reach every cell in the body, and carbon dioxide and other waste products to be removed.
First aid implications
With the exception of the fingernails, toenails and hair, injury to any part of the body will result in damage to blood vessels and, therefore, bleeding.
For all organs and parts of the body to receive adequate oxygen, they need lungs that are being ventilated to get oxygen into the blood, and a heart that is beating to pump the oxygenated blood around the body and supply all organs, especially the brain.