Capillarie

Notes

Capillaries Learning Point 4. Describe capillaries and state how capillary beds can be opened and closed depending on the body's needs. The capillaries are the smallest blood vessels in the human body. The function of capillaries is to bring blood close to body cells in order to supply them with oxygen and nutrients and to carry away their waste materials, such as carbon dioxide. The exchange of materials between blood and body tissues at the level of the capillaries is facilitated by specific structural features of capillaries. Capillary walls are very thin, just one cell thick, which facilitates the process of exchange of materials with body cells. Also, most capillaries are only wide enough to let red blood cells pass into the capillary one cell at a time, which results in a slow blood flow inside these blood vessels and gives enough time for the movement of materials to and from body tissues. Moreover, capillary walls have small spaces between their cells, which allow some substances to leak. Some types of capillaries also have large gaps and pores in their walls, which further facilitate the exchange of materials with body tissues, since materials can leave and enter the capil...