Whole blood or plasma clots upon standing and if the clot is removed, the remaining straw colored fluid is called serum. Serum contains a variety of small molecular weight components as well as hundreds of different serum proteins. The serum proteins are usually divided into albumin and globulin classes.
Serum albumin is the major protein found in serum.
Albumin functions in the transport of many substances in blood and plays an important role in the control of plasma osmolarity. The serum globulins can be subdivided into three major fractions. These fractions are the alpha, beta, and gamma globulins. Each globulin fraction contains a large number of different proteins. For example, the protein transferrin is only one of the proteins found in the beta -globulin fraction.