The Plasma Proteins

Although many blood-borne hormones (such as insulin) are proteins, and all enzymes (in the blood and elsewhere) are proteins, the majority of proteins found in the bloodstream are called the plasma proteins.

There are three broad types of plasma proteins: the albumins (al-BYOO-mins), globulins (GLAHB-you-lins), and the clotting proteins. All of them are important synthesis products of the liver.

The albumins

The word, albumin, comes from the Latin for ''white of an egg.'' The albumins are thick, sticky, glue-like proteins found in raw egg white and in various other plant and animal tissues. The albumins are the most abundant of the plasma proteins, making up about 60% of the total. Because they are so abundant, their concentration can significantly affect the water concentration within the blood plasma. When the blood albumin concentration is unusually high, for instance, the water concentration within the bloodstream is unusually low. As a result, there is a net osmosis (diffusion) of water from the surrounding body tissues, into the blood plasma. Such significant movements of H2O into and out of the bloodstream, have important influences upon both the blood volume and blood pressure.

The globulins

The word, globulin, exactly translates to mean a ''little globe'' (globul) ''protein substance'' (-in). This rather rounded, globe-shaped group makes up about 1/3 (36%) of all the plasma proteins. There are several subtypes of globulins, usually named with some of the letters of the Greek alphabet. The alpha and beta globulins, for instance, are transport proteins that carry lipids, certain ions, and fat-soluble (dissolvable) vitamins. Another main subtype is the gamma (GAM-ah) globulins. These serve as antibody molecules that attack and destroy foreign invaders as a critical part of the body's immune (ih-MYOON) or self-defense system.

The clotting proteins

The last main subtype of plasma proteins comprises the clotting proteins, which make up about 4% of the total. The two most important clotting proteins are called fibrinogen (feye-BRIN-oh-jen) and prothrombin (proh-THRAM-bin). Fibrinogen and prothrombin are present in the blood plasma all the time.

They undergo a sequence of reactions to help produce blood clotting, whenever there is some damage or injury to the blood vessel wall. In summation:

THE PLASMA - ALBUMINS + GLOBULINS + CLOTTING PROTEINS (Osmosis, blood (Transport, PROTEINS volume, BP) immunity) (Blood clotting)

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