Definition
- Plasma proteins are the major solute constituents of plasma; normal concentration 6 to 8 g/100 mL (g%), synthesized mainly by the liver.
- Three types: albumin, globulin and fibrinogen.
Types of Plasma Proteins
Types of plasma proteins
Type
Albumin
- Normal concentration
- 4 to 5.5 g%
- Site of synthesis
- Liver
Globulin
- Normal concentration
- 1.5 to 3 g%
- Site of synthesis
- Liver, reticuloendothelial system cells, plasma cells
Fibrinogen
- Normal concentration
- 0.3 g%
- Site of synthesis
- Liver
- Globulins subdivide into α (α1, α2), β (β1, β2) and γ; γ-globulins are antibodies (immunoglobulins) formed by plasma cells.
- Albumin is the smallest plasma protein by molecular size and determines the colloidal osmotic (oncotic) pressure of plasma.
- Fibrinogen is essential for blood coagulation (forms fibrin, the final step) and contributes to plasma viscosity and ESR.
- Albumin:Globulin ratio (AGR) is normally 1.7:1 (1.2 to 2.2:1).
- Albumin MW 66,000 Da, half-life about 20 days; globulin MW 90,000 to 156,000 Da; fibrinogen MW 340,000 Da.
- Globulins include transport proteins (transferrin, ceruloplasmin, hemopexin) and form lipoproteins in combination with plasma lipids.