What Proteins Are in Blood Plasma?

Blood is a highly specialized form of connective tissue composed of several cellular elements and a fluid element. The cellular elements of blood determine its categorization as red or white blood cells, or as platelets. The fluid element is known as blood plasma. This plasma is composed of water, proteins, hormones, vitamins, amino acids, lipids, carbohydrates and inorganic salts. Next to water, which comprises 90 percent of its composition, the most important elements in blood plasma are the three blood plasma proteins: albumins, globulins, and fibrinogen.

A lab technician examines blood plasma. (Image: DragonImages/iStock/Getty Images)

Albumin

Albumin makes up the largest proportion of blood plasma proteins. Albumin is manufactured by the liver and is responsible for keeping the fluid pressure level constant in the blood, so that blood continually flows in the bloodstream rather than seeping into surrounding tissues. Albumin also functions as a carrier, binding specific molecules in the blood plasma so that it can carry nutrients and vitamins where they are needed in the body. Albumin levels act as strong indicators of health; low levels of albumin can indicate several potentially dangerous medical conditions, such as severe dehydration, liver damage and kidney failure.

Globulin

Although globulins make up a smaller proportion of blood plasma protein, they perform the very important function of providing antibodies. Globulin protein is actually subdivided into four major categories: gamma globulin, alpha-1 globulin, alpha-2 globulin, and beta globulin. Gamma globulins are also classified as immunoglobulin and are the specific group of plasma protein that functions as antibodies providing protection against disease on a cellular level. The alpha and beta globulins primarily act as transporters for fat soluble vitamins, hormones and lipids. The alpha and beta globulins are synthesized in the liver; gamma globulins, however, are created by the lymphoid tissue.

Fibrinogen

Fibrinogen is also created by the liver. Its primary function is to work with blood platelets to create blood clots. Abnormally low levels of fibrinogen can lead to excessive bleeding and hemorrhaging. Elevated levels of fibrinogen, however, can be a strong predictor of stroke. A recent study lead by Dr. Rehana Lovely of Missouri State University and published in the March 2010 issue of "Clinical Chemistry" indicates that a particular subset of the fibrinogen protein, known as y' fibrinogen, specifically may be useful as a marker for determining risk factor for cardiovascular disease. According to the study, y' fibrinogen levels can serve as an accurate biomarker for cardiovascular risk even in patients who show normal, healthy cholesterol levels—potentially saving lives in patients who would have, in the past, been considered low risk.

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