Capillaries are tiny blood vessels where the smallest arteries meet the smallest veins and where the blood exchanges food and oxygen for waste products. Veins, which are also blood vessels, return depleted blood to the heart.Know More
Some capillaries are so small that they can only be seen under a microscope, and tiny blood cells can only pass through them one at a time. Because capillaries are so small, their walls are correspondingly thin. Nutrients carried by the blood are able to pass through these walls to the cells of the body. Waste materials from the cells and tissues can also pass through the walls and be carried away. In the lungs, the capillaries exchange oxygen and carbon dioxide.
Capillary-sized veins are called venules. The small veins join together to form larger ones. Eventually, the veins all flow into the superior and inferior vena cava. The superior vena cava carries blood to the heart via the head and arms. The inferior vena cava carries blood from the legs and the trunk.
The walls of veins have three layers, though they're thinner and more rigid than the walls of the arteries. Many of the larger veins have valves that make sure the blood flows toward the heart and doesn't flow backward.Learn more about Blood
The purpose of the precipillary sphincter is to adjust the flow of blood into the capillaries. These smooth muscles contract and act as a valve to redirect blood to the area where the body needs it most. They encircle each capillary branch at its exit from the arteriole, according to Reference.com.Full Answer >
The capillaries that contain a complete lining are called continuous capillaries. The lining itself is referred to as the endothelial lining. Variations in this lining determine the "leakiness" of the capillary.Full Answer >
White blood cells emerge from the bloodstream through capillaries and engage harmful molecules by either engulfing them or poisoning them. There are different types of white blood cells, which divide between them various infection-fighting activities, from detection to elimination.Full Answer >
Blood, a liquid made up of plasma and cells, has several functions including controlling body temperature, supplying oxygen and nutrients, removing waste, assisting the immune system and transporting hormones. Blood cells, red and white, are made in bone marrow. Plasma is 90 percent water but contains dissolved substances such as hormones, electrolytes, vitamins and proteins.Full Answer >