Plasma Proteins of blood in animals

Plasma Proteins of blood in animals

Plasma proteins of blood in animals contribute about 7% of the total organic molecules of the plasma. The major proteins present in plasma are- Albumin (55%), Globulins (38 %) and Fibrinogen (7 %).

Liver functions as a chief site of synthesis of plasma proteins, albumin, fibrinogen, prothrombin and some of the globulins. While the gamma globulins are synthesised extra-hepatically in the lymph nodes and in the Mononuclear Phagocytic System (MPS) of spleen and bone marrow.

The ratio of albumin to globulin is 1:0.7. There are species variations in the ratio of plasma proteins i.e. albumin: globulin ratio. In humans, sheep, goats and dogs, the albumin predominates over globulin.

In horses, pigs, cow and cats albumin globulin ratio is equal. In new born animals (except rodents and primates plasma gamma globulin is absent or found in minute quantity.

Separation Method of plasma proteins

1. Salting out method: Using different concentrations of ammonium sulphate solution.
2. Electrophoresis: Paper, starch gel, polyacrylamide gel electrophoresis are used for the separation of plasma protein fractions.

PLASMA PROTEIN FRACTIONS

Prealbumin

Transports thyroxine and Vitamin A.

Albumin

• Two fifth is intravascular and the rest occur extravas­cularly. It provides colloidal osmotic pressure because of its high concentration and low molecular weight and non-diffusible property through blood vessels, thus prevents excessive passage of fluid from the blood into the interstitial tissue and serves to control the fluid balance between blood and tissues.
• It contributes to the amino acid pool with tissue protein and helps in transport of some anions and cations.

Globulins

Globulins Includes fractions α1 and α2, β1 and β2 and γ globulins which include IgA, IgD,IgE, IgG and IgM.

•  α – globulins act as carrier proteins of bilirubin, lipids, steroids and thyroxine.
• α₁ globulins are protease inhibitors and functions to inhibit WBC elastase and other WBC proteases and activated factor XI. The α₁ lipoproteins transport lipids, fat soluble vitamins and hormones.
• α₂ globulins are the macroglobulins and inhibit plasmin, thrombin and kallikrein.
• β – globulins  are:
  1. Ceruloplasmin: Transports copper.
  2. Ferroxidase: Transferrin transports iron.
  3. Haptaglobulin: Transports Hb to liver after haemolysis.
  4. Apolipoproteins: Transports triglycerides, phospholipids and cholesterol.
  5. Hemopexin: Aids the transport of heme from lysed RBCs.
  6. Transcortin: Transports cortisol.
  7. Transcobalamins I & II: Transports cobalt.
• γ – globulins
  1. They provide viscosity to the blood, thus maintain normal blood pressure. Synthesised by -lymphocytes and plasma cells, functions to provide immunity and also helps transport of vitamin D.
  2. The γ globulins are the immunoglobulins (Ig) and are classified into the following types:
  3. IgG is responsible for most of the humoral immunity of the organism. It can cross placenta.
  4. IgM is the second major immunoglobulin of the serum and it is typically the first immunoglobulin increase in concentration in serum during primary immune response. These are naturally occurring antibodies against erythrocytes in certain incompatible blood types.
  5. IgA is a glycoprotein found in external secretion such as saliva, tears, colostrum etc. It forms the primary immunoglobulin in the colostrum and is responsible for natural passive immunity in the neo-natal calf, foal, lamb, kid and piglets. Plays an important role in local defence by protecting various body surfaces e.g., the intestinal, respiratory and uro-genital tracts, mammary gland and the eyes from bacterial and viral invasions. IgA does not cross the placenta. It is most abundantly found in normal animals.
  6. IgD is involved in B-cell differentiation to form ‘clones’.
  7. IgE is involved in hypersensitivity and allergic responses. It causes the release of histamine from basophils and mast cells.

Fibrinogen

Fraction from the liver, functions as a precursor to form a mesh work of fibrin threads and play a key role in blood coagulation. It influences the suspension stability of the erythrocytes. Increased concentration of fibrinogen and globulins alter the colloidal state of the blood, hastens agglutination of RBCs and settling.

FUNCTIONS OF PLASMA PROTEINS

1. Function as source of amino acids for the synthesis of tissue proteins. The amino acids of plasma protein and tissue pro­teins are in a state of dynamic equilibrium.
2. Provide colloidal osmotic pressure and helps to regulate fluid balance. Around 80% of the colloidal osmotic pressure is contributed by albumin.
3. They act as blood buffer and regulate acid-base balance, thus maintains normal pH of 7.4.
4. Fibrinogen and various clotting factors are essential for coagulation of blood.
5. Influence the suspension stability of RBCs in the blood.
6. Contributes to the viscosity of plasma (by gamma globulins), thereby providing for peripheral resistance, which is essential for efficient cardiac function.
7. As carrier proteins they are invloved in transport of copper, iron, heme, bilirubin, thyroxine, cortisol, sex hormones, vitamin A, vitamin D, fatty acids, triglycerides, phospholipids and cholesterol.
8. Immunoglobulins provide specific antibody against specific antigen.

PLASMA PROTEIN CONCENTRATION