PLASMA PROTEINS

Introduction: Plasma proteins are: Serum albumin. Serum globulin. Fibrinogen. Serum contains albumin and globulin. Fibrinogen is absent Converted into fibrin during blood clotting. Therefore albumin and globulin are called serum albumin and serum globulin.

Normal values: Total proteins: 7.3 g/dL Albumin/ globulin ratio: Serum albumin : 4.7 g/dL Serum globulin : 2.3 g/dL Fibrinogen : 0.3 g/dL Albumin/ globulin ratio: Important indicator of diseases involving liver or kidney. Nomal A/G ratio is 2:1.

Origin of plasma proteins: In embryo: Mesenchyme cells. 1st: albumin. Others synthesized later. In adults: Reticuloendothelial cells of liver. Also from spleen, bone marrow, disintegrating blood cells and general tissue cells. Gamma globulin is synthesized from B lymphocytes.

Properties of plasma proteins: Molecular weight: Albumin: 69,000 Globulin: 1,56,000 Fibrinogen: 4,00,000 Oncotic pressure: Responsible for osmotic pressure in blood. Colloidal osmotic pressure. 25 mm Hg. Specific gravity: 1.026. Buffer action: Acceptance of hydrogen ions. 1/6 of total buffering action.

Functions of plasma proteins: 1. ROLE IN COAGULATION OF BLOOD: Fibrinogen is essential for coagulation. 2. ROLE IN DEFENCE MECHANISM: Gamma globulins acts as antibodies. Immunoglobulins. 3. ROLE IN TRANSPORT MECHANISM: Albumin, alpha globulin and beta globulin are responsible for transport of hormones, enzymes, etc. Alpha and beta globulins play an important role in transport of metals in blood. 4. ROLE IN MAINTENANCE OF OSMOTIC PRESSURE IN BLOOD: Plasma proteins can’t pass through capillary membranes and remain in blood. They exert osmotic pressure of 25 mmHg. Albumin exerts maximum pressure. Starling hypothesis: net filtration through capillaries is proportional to hydrostatic pressure difference minus oncotic pressure difference.

5. ROLE IN REGULATION OF ACID BASE BALANCE: Ability of proteins to take up hydrogen ions. 6. ROLE IN VISCOSITY OF BLOOD: Provide viscosity to maintain blood pressure. 7. ROLE IN ERYTHROCYTE SEDEMENTATION RATE: Globulin and fibrinogen accelerate the tendency of rouleax formation by RBCs. 8. ROLE IN SUSPENSION STABILITY OF RBCs: Globulin and fibrinogen helps in suspension stability of RBCs. 9. ROLE IN PRODUCTION OF TREPHONE SUBSTANCES: Produced by leukocytes from plasma proteins. 10. ROLE AS RESERVE PROTEINS: Used as source of energy. Plasma proteins are split into amino acids by tissue macrophages. Amino acids are taken back by blood and distributed throughout the body to form cellular protein molecules.

PLASMAPHERESIS: Experimental procedure done in animals to demonstrate the importance of plasma proteins. Also called whipple’s experiment. Procedure: Demonstrated in dogs. Blood is removed completely from body. RBCs are separated from plasma, washed with saline and reinfused into the body of same dog along with locke’s solution. Sudden lack of proteins results in state of shock. High protein diet results in restoration of proteins in 7 days. New plasma proteins are synthesized by liver of dogs. High protein diet after removal of liver-> plasma proteins are not produced. Persistant shock results in death.

Plasmapheresis demonstrates: Importance of plasma proteins for survival. Synthesis of plasma proteins by liver.

Clinical significance: Blood purification procedure. Effective for temporary treatment of autoimmune diseases. Immune system attacks body’s own tissues. Antibodies are protein in nature that circulate in the blood before attacking tissues. Plasmapheresis removes these antibodies from blood. Also called therapeutic plasma exchange.

Procedure: Venous blood removed. Blood cells are separated from plasma by cell separator. Anticoagulant prevents clotting of blood. After removal. Plasma is discarded and cells are returned cells are returned to blood stream by mixing with saline and sterilized human albumin protein.

Uses of plasmapheresis: Used to remove antibodies from blood. Temporary benefit of protecting the tissues from antibodies. Required repetitive session of the treatment. Diseases: Mysthenia gravis. Thrombocytopenia purpura. Paraproteinimic peripheral neuropathy. Chronic demylenating polyneuropathy. Guillain barre syndrome. Lambert Eaton myasthenic syndrome.