University of Edinburgh

BSL Biology Glossary - capillary - definition

Definition: Capillaries are very small tubes that carry blood. Blood cells go down the thick arteries into the thinner capillaries. The capillaries get narrower and narrower. The red blood cells carry oxygen with them and other nutrients. When the blood gets to the capillaries it releases the oxygen and the nutrients, which filter through into the tissues. In the tissues there are waste products like carbon dioxide ( CO²). These pass into the blood stream and the blood leaves the capillaries