Capillary

Capillary, one of the minute blood vessels that form the connection between the arteries and the veins. These tiny vessels vary in diameter from 0.0127 to about 0.2032 mm (0.0005 to about 0.008 in) and are present in great numbers throughout the entire body. The walls of capillaries are exceedingly thin and readily permeable. They are surrounded by lymph, and there is a constant interchange between the substances in the blood within the capillaries and the waste products in the body tissues and lymph outside. This interchange facilitates the processes of nutrition and elimination and enables the exchange of oxygen and carbon dioxide to take place. Lymph capillaries assist the blood capillaries in this process.