10-16. RESPONSES TO HEMORRHAGE
A blood vessel may be damaged by transection (cutting across) or rupture. At
such points, a volume of whole blood can flow out of the blood vessels. This escape of
blood from the blood vessels is called hemorrhage.
HEMO = blood
RRHAGE = excessive flow ("bursting forth")
a. Vascular contraction. The first response to a cut or ruptured vessels is
contraction (spasm) of the blood vessel itself. This may considerably reduce the
volume of blood loss.
b. Platelet Plug. If the hole is small, a plug formed by clumping of the platelets
c. Blood Clotting. There is a complicated process for sealing off holes or ends
of blood vessels after a cut or rupture. By this process, called coagulation or clotting,
the blood forms a solid mass to seal the opening where the blood is escaping. The
mass is called a blood clot. After many intermediate steps, the protein fibrinogen of the
blood is converted into sticky strands of fibrin. These sticky strands adhere to the wall
of the opening and form a meshwork in the opening, which traps RBCs and plasma.
Thus, the opening is sealed.
d. Hematoma. A hematoma is a collection of blood, usually clotted, in an
organ, space, or tissue. When found immediately beneath the skin, it will produce a
purplish spot or mark. With time, as the clot is broken down and resorbed, the
hematoma changes color and becomes smaller.
e. Mobilization of Blood Reservoirs. Certain areas of the body contain
enough blood that they can be used as reservoirs to maintain the circulating blood
volume. This is important when a volume of blood has been lost through hemorrhage.
Among these are the spleen and the liver, whose sinuses together can release several
hundred milliliters of blood. Also important are several groups of veins, including the
large abdominal veins, which can also provide several hundred milliliters of blood.
10-17. BLOOD TRANSFUSIONS AND BLOOD MATCHING
a. Transfusions. In cases where an individual has lost whole blood by
hemorrhaging, it is often necessary to give transfusions of whole blood. Whole blood
transfusions continue the functions of the RBCs. On the other hand, if an individual has
suffered burns causing a loss of fluid but not the loss of formed elements, plasma or a
plasma substitute will often be used.