Plasma
(Encarta)
COMPOSITION OF BLOODAbout 55 percent of the blood is composed of a liquid known as
plasma. The rest of the blood is made of three major types of
cells: red blood cells (also known as erythrocytes), white blood cells
(leukocytes), and platelets (thrombocytes).
Plasma consists predominantly of water
and salts. The kidneys carefully maintain the salt concentration in plasma
because small changes in its concentration will cause cells in the body to
function improperly. In extreme conditions this can result in seizures, coma, or
even death. The pH of plasma, the common measurement of the plasma?s acidity, is
also carefully controlled by the kidneys within the neutral range of 6.8 to 7.7.
Plasma also contains other small molecules, including vitamins, minerals,
nutrients, and waste products. The concentrations of all of these molecules must
be carefully regulated.
Plasma is usually yellow in color due to
proteins dissolved in it. However, after a person eats a fatty meal, that
person?s plasma temporarily develops a milky color as the blood carries the
ingested fats from the intestines to other organs of the body.
Plasma carries a large number of
important proteins, including albumin, gamma globulin, and clotting
factors. Albumin is the main protein in blood. It helps regulate the water
content of tissues and blood. Gamma globulin is composed of tens of thousands of
unique antibody molecules. Antibodies neutralize or help destroy
infectious organisms. Each antibody is designed to target one specific invading
organism. For example, chicken pox antibody will target chicken pox virus, but
will leave an influenza virus unharmed. Clotting factors, such as fibrinogen,
are involved in forming blood clots that seal leaks after an injury. Plasma that
has had the clotting factors removed is called serum. Both serum
and plasma are easy to store and have many medical uses.
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