The smallest of the body's blood vessels. Capillaries have walls so thin that oxygen
and glucose can pass through them and enter the cells, and waste products such as carbon
dioxide can pass back into the blood to be carried away and taken out of the body.
Sometimes people who have had diabetes for a long time find that their capillaries become
weak, especially those in the kidney and the retina of the eye.
Here is a diagram of a capillary,