PLASMA PROTIENS

 

1.Functions of plasma proteins

   Important plasma proteins are Albumin, Globulin & Fibrinogen

       Normal Albumin/Globulin ratio = 1.7 : 1

a.       Colloidal osmotic pressure: Albumin is mainly responsible for the development of colloidal osmotic pressure. The normal colloidal osmotic pressure of blood is 25-30 mmHg. This is mainly responsible for the passage of fluid across the capillary membrane

b.      Viscosity of blood: Globulin maintains the viscosity of blood to some extent. Viscosity is one of factors that influence blood pressure

c.       Immunity: Antibodies (Immunoglobulins) belong to gammaglobulins. Antibodies neutralize the antigen

d.      Coagulation: Both prothrombin & fibrinogen take part in clotting process

                            Prothrombin activator 

                                                                                                                                    

             Prothrombin                                 Thrombin

                                   

                                            Fibrinogen                               Fibrin (clot)

e.       Transport:

  i) CO₂ is transported by carbamino proteins

 ii) Transferrin – transports iron

iii) Ceruloplasmin – transports copper

iv) TBG – Thyroxine Bound Globulin

v)  CBG – Cortisol Bound Globulin

f.       Acid-Base Balance – Plasma proteins act as buffers & neutralize any change in blood pH

g.      Protein reserve – Serve as storehouse of protein. Provides proteins to tissues during starvation

h.      ESR : Fibrinogen & Globulin increase the ESR. Albumin decreases the ESR

i.        Haptoglobin: Forms the complex with hemoglobin & prevent its filtration into the kidney

                                    2. ANTICOAGULANTS

               Anticoagulants are the substances that prevent clotting

a.       Natural anticoagulants:

        Heparin – produced by mast cells & basophils

        Mechanism of action: facilitates antithrombin – III which inhibits the clotting                       

                            factors II, IX, XI & XII

b.      Anticoagulants used in blood bank:

     Acid Citrate Dextrose (ACD): Calcium chelating agent

     Mechanism of action: forms a complex with calcium ions and decreases ionic 

                                         calcium level

c.       Anticoagulants used in the laboratories:

   Sodium citrate – Forms double salt with calcium ions

         Double oxalate (Oxalates of K+ & NH4) - Precipitation of calcium

                  EDTA- Ethylene Diamine tetra acetate – Preparation of calcium ions

d.      Therapeutic anti coagulants:

Dicoumarol – prevents the synthesis of blood clotting factors II, VII, IX, X by competitive inhibition with vitamin .K.