Figure 1-4. Contusion.
b. Wound Healing. Wound healing is a complicated process. A wound is a
break in the continuity of tissue. The body must have a special procedure to take care
of the skin injury and dead tissue. The injured area must be able to signal distress, and
there must be some way to get rid of the dead cells and replace them with new cells.
The process of wound healing is a way of restoring living tissue so that the entire body
is covered with skin.
(1) The body's first response to cell damage is inflammation. The reaction
is similar regardless of the cause--cut, burn, bruise, or pinch. The injury starts a
reaction which may be the release from the dead or injured cells of one of their
substances such as histamine. The released substances affect the capillaries. The
capillaries dilate, widely increasing the blood supply that they can bring to the injured
area. If the injury takes place in the skin or in the tissue close to the skin, the increased
amount of blood in that area causes the area to look red. Because the injured area has
a greater blood supply than the surrounding area, the wound site is warm to the touch.
(2) As the capillaries dilate, the "mesh" of their walls also is opened.
Normally, capillary walls allow water and electrolytes to pass through, but now these
walls also permit extra fluid and some protein plasma to escape. This extra fluid in
tissue spaces produces swelling. Because the fluid is extra, the patient feels discomfort
and a throbbing sensation. Sometimes just the swelling is enough to stimulate the pain
receptors. The changes in the blood vessels are responsible for the basic symptoms of
inflammation: swelling, pain, redness, and heat.
(3) One of the substances released by injured cells attracts leukocytes.
Leukocytes pass through capillary walls into damaged tissues. In an injury with
extensive tissue damage, large amounts of the substance which attracts leukocytes are
released. This substance may be absorbed and circulated in the blood stimulating the
production of more white cells. If a blood count is taken at this time, there will be an
increase above normal in the number of white cells (leukocytosis).