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40.2E: Plasma and Serum

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    • Contributed by Boundless
    • General Microbiology at Boundless

    Plasma is the liquid component of blood after all of the cells and platelets are removed; serum is plasma after coagulation factors have been removed.

    Learning Objectives

    • Explain the structure and function of plasma and serum

    Key Points

    • Plasma, the liquid component of blood, comprises 55 percent of the total blood volume.
    • Plasma is composed of 90 percent water with antibodies, coagulation factors, and other substances such as electrolytes, lipids, and proteins required for maintaining the body.
    • The removal of coagulation factors from plasma leaves a fluid similar to interstitial fluid, known as serum.
    • Albumin, a protein produced in the liver, comprises about one-half of the blood serum proteins; it functions to maintain osmotic pressures and to transport hormones and fatty acids.
    • Immunoglobin is a protein antibody produced in the mucosal lining; it plays an important role in antibody mediated immunity.

    Key Terms

    • interstitial fluid: a solution found in tissue spaces that inundates and moistens cells in multicellular animals
    • electrolyte: any of the various ions (such as sodium or chloride) that regulate the electric charge on cells and the flow of water across their membranes
    • viscosity: a quantity expressing the magnitude of internal friction in a fluid, as measured by the force per unit area resisting uniform flow
    Figure \(\PageIndex{1}\): Blood sample after centrifugation: The liquid components of blood called plasma (yellow section) can be separated from the erythrocytes (red section) and platelets (white section) by using a centrifuging or spinning the blood.

    Plasma and Serum

    Plasma, the liquid component of blood, comprises 55 percent of the total blood volume. It can separated by artificially spinning or centrifuging the blood at high rotations of 3000 rpm or higher. The blood cells and platelets that make up about 45 percent of the blood are separated by centrifugal forces to the bottom of a specimen tube, leaving the plasma as the upper layer. Plasma consists of 90 percent water along with various substances required for maintaining the body’s pH, osmotic load, and for protecting the body. The plasma also contains the coagulation factors and antibodies.

    Serum, the plasma component of blood which lacks coagulation factors, is similar to interstitial fluid in which the correct composition of key ions acting as electrolytes is essential for normal functioning of muscles and nerves. Other components in the serum include proteins, which assist with maintaining pH and osmotic balance while giving viscosity to the blood; antibodies, or specialized proteins that are important for defense against viruses and bacteria; lipids, including cholesterol, which are transported in the serum; and various other substances including nutrients, hormones, metabolic waste, and external substances, such as drugs, viruses, and bacteria.

    Human serum albumin, the most abundant protein in human blood plasma, is synthesized in the liver. Albumin, which constitutes about one-half of the blood serum protein, transports hormones and fatty acids, buffers pH, and maintains osmotic pressures. Immunoglobin, a protein antibody produced in the mucosal lining, plays an important role in antibody mediated immunity.



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