What is the capillaries?

Capillaries are the smallest blood vessels in the body, forming a network that connects arterioles to venules. They are composed of a single layer of endothelial cells, which are thin and porous enough to allow for the exchange of substances between the blood and the surrounding tissues.

Capillaries are found in all tissues and organs of the body, and their function is to deliver oxygen and nutrients to the cells, and to remove waste products. The exchange of substances between the blood and the tissues occurs by diffusion, which is the movement of molecules from an area of high concentration to an area of low concentration.

The diameter of capillaries is typically between 5 and 10 microns (μm), which is about the same size as a red blood cell. This allows red blood cells to pass through capillaries in single file, and it also helps to maintain a high surface area for the exchange of substances.

The walls of capillaries are made up of endothelial cells, which are thin and flattened cells with a large number of pores. These pores allow for the passage of water, solutes, and small molecules, but they prevent the passage of larger molecules such as proteins.

The endothelial cells of capillaries are also responsible for the production of a number of substances that help to regulate blood flow and the exchange of substances between the blood and the tissues. These substances include nitric oxide, prostacyclin, and endothelin.

Capillaries are essential for the proper functioning of the body. They provide the cells with the oxygen and nutrients they need to survive, and they remove waste products that could be harmful to the body.