How is the structure of a capillary related to its function?

The capillaries are very small blood vessels in the body that take the blood to the individual body cells. They transport oxygen and nutrients to the cells ( the cell needs these to survive) and remove carbon dioxide and waste products. It is within these vessels that the exchange of these products happens between the body cells and the blood vessel. Capillaries have very thin walls that are only 1 cell thick. These walls are also very permeable (leaky!!). This allows the carbon dioxide, oxygen and nutrients to diffuse between cells and vessels. They carry blood at a very low pressure so don't need any muscular walls.