Unlike the arteries and veins, capillaries are very thin and fragile. The capillaries are
actually only one
epithelial cell thick. They are so thin that blood cells can only pass through them in
single file. The
exchange of oxygen and carbon dioxide takes place through the thin capillary wall. The red
cells inside the capillary release their oxygen which passes through the wall and into the
tissue. The tissue releases its waste products, like carbon dioxide, which passes through
the wall and
into the red blood cells.
and veins run
parallel throughout the body with a web-like network of capillaries, embedded
in tissue, connecting them. The arteries pass their oxygen-rich blood to the capillaries
which allow the
exchange of gases within the tissue. The capillaries then pass their waste-rich blood to
the veins for
transport back to the heart. Capillaries are also involved in the body's release of excess
exercise, for example, your body and blood temperature rises. To help release this excess
blood delivers the heat to the capillaries which then rapidly release it to the tissue.
The result is that
your skin takes on a flushed, red appearance. If you hold your hand, for example, under
your hand will quickly turn red for the same reason. Your arm, however, is not likely to
because it is not actually feeling an increase in temperature.