neutralized by the bicarbonate buffer system, the blood would rapidly become too acid.
The buffer systems of the blood are so sensitive that the blood pH is held at an almost
constant level of about 7.40.
e. Water Balance. The maintenance of normal fluid distribution and water
balance in the body depends on the mobility of the water found in the blood. The
osmotic pressure of the plasma proteins is of great physiologic importance in the
regulation of the movements of fluid between the capillaries and the tissue spaces.
f. Regulation of Body Temperature. Mammalian tissue can function with
maximal efficiency only within closely restricted limits of body temperature. The
metabolic processes, which occur during cell activity are constantly producing heat.
Since blood passes through the capillaries of all organs, it tends to redistribute the heat
produced in these areas. The circulation of blood in the vessels of the skin and lungs
g. Regulation of Hormone Transport. The effectiveness of hormones is
entirely dependent on the circulation of blood. The transport to the tissues of various
hormones of the glands is carried out entirely by the blood.
The formed elements of blood and the phenomenon of coagulation are
discussed in detail in Subcourse MD0853, Hematology. Therefore, no review
is given here.
a. Composition. Plasma is the fluid part of blood obtained by separating the
formed elements from whole blood. Plasma is a clear, straw colored liquid that contains
a large number of substances in solution. Plasma makes up about 55 percent of whole
blood. Plasma is about 91.5 percent water and 7 percent protein (albumins, globulins,
fibrinogen, and prothrombin). The remainder includes inorganic salts, lipids, enzymes,
hormones, vitamins, and carbohydrates.
b. Functions of Plasma.
(1) Suspension medium. Since plasma comprises 55 one of the functions
of plasma is to act as a suspension medium for the formed elements. Blood cells are
kept suspended and circulating in a bath of plasma. Plasma also keeps the proper
volume of fluid circulating throughout the body.
(2) Coagulation. The factors for the process of coagulation, which is
characteristic of blood, are contained chiefly within the plasma fraction of the blood.
Platelets, of course, contribute to the clotting mechanism. It is the plasma protein,
fibrinogen, however, which is the soluble precursor of the jellylike fibrin in a blood clot.