Plasma

Blood plasma consists of the liquid part of blood and makes up about 55% of the blood volume. It contains 90–91% water, while the remaining 9–10% consists of organic and inorganic substances. About 85% of the organic substances are proteins, approximately 65–85 g/l. The liver and reticuloendothelial system synthesize blood plasma proteins, which perform various physiological functions:

• They maintain colloid osmotic pressure and stabilize blood volume. Albumins regulate blood plasma volume and fluid balance between tissues, with about 80% of plasma osmotic pressure depending on them. When albumins fall below 30 g/l, colloid osmotic pressure decreases, causing fluids to move from the blood into tissues, leading to edema. The relatively lower blood plasma volume decreases renal blood flow, stimulating the renin-angiotensin-aldosterone system to restore blood volume. Without albumin to retain Na+ and other cations and water, water spreads into the interstitial space, increasing edema.

• Blood plasma proteins provide a small reserve of body proteins.

• Albumins serve as the main transport proteins, carrying free fatty acids, unconjugated bilirubin, Ca2+, Cu2+, tryptophan, triiodothyronine, and many drugs (e.g., aspirin, dicumarol, sulfonamides).

• Proteins, as amphoteric compounds, help maintain stable blood pH.

• Blood plasma proteins, including fibrinogen and others, assist in blood clotting.

Researchers have currently identified about 100 blood plasma proteins. Blood serum electrophoresis determines five fractions: albumins, a1-, a2-, b-, and g-globulins. Various electrophoresis and immunoelectrophoresis methods can identify more than 30 fractions.