Blood and Plasma Proteins

Question 1

types of Plasma proteins

Answer 1

• normal plasma protein conc. 6-8 g/100 ml of plasma

the major types of plasma proteins are:
1) albumin
-major constituent of plasma proteins (4.5 g/dl)
- formed in liver
- half life is about 20 days
- maintains the blood colloid osmotic pressure
- carrier protein
- buffering capacity for acid-base balance
- being smallest in diameter, in kidney diseases with glomerular injury it appears early in urine (albuminuria)
- in kidney diseases, albuminuria - dec albumin - hypoalbuminemia.
it also occurs in liver due to dec formation of albumin.
- therefore, decreased blood colloidal osmotic pressure leads to edema

2) globulin:
- formed in liver by cells of reticuloendothelial system and plasma cells
- 2.5 g/dl
- globulins are divided into three categories, a(a1,a2), b(b1,b2) and gamma
- include diff transport proteins, transferrin, ceruloplasmin, hemopexin etc.
transferrin - iron transport
ceruloplasmin- copper transport
hemopexin - heme binding and transport
- antibodies are gamma globulins formed by plasma cells

normal albumin: globulin = 1.7:1 (1.2 to 2.2:1)
- detection of agr helps in diagnosing and prognosis

3) fibrinogen
- produced in liver
- plays an imp role in blood coagulation
- also contributes to viscosity of plasma and determination of ESR.

Question 2

functions of plasma proteins

Answer 2

1) osmotic pressure: plasma proteins are osmotically active molecules and the osmotic pressure of plasma due to plasma proteins is called oncotic pressure.
- normal - 25 mm hg
- helps in maintaining volume of vascular compartment - retains fluid - therefore prevents loss of fluid from capillaries into the interstitial tissue space.
- so when oncotic pressure decreases due to hypoproteinemia as occurs in liver and kidney diseases, edema manifests due to escape of water into the interstitial tissue space.
- due to presence of albumin

2) viscosity of blood :
- contributes to 50% viscosity of blood
- fibrinogen molecules that are elongated and fibrillar in shape contribute more to blood viscosity than albumin molecules that are ellipsoid in structure.

3) immunity:
- antibodies - plasma proteins- gamma globulins
- antibodies mediate humoral immunity that protects the body from infections especially extracellular pathogens and from the effect of toxic substances

4) blood coagulation:
- blood clotting depends on conc of fibrinogen that forms fibrin thread
- blood clotting factors like prothrombin are also plasma proteins

5) carrier proteins : serve as carrier molecule for transport of various substances like hormones, drugs, metals, etc
- carrier for water-insoluble (lipophilic) substances - albumin - steroid hormones, fatty acids and thyroid hormones
- specific carrier proteins - meant for transport of lipophilic hormones to target cells.
eg - sex hormone-binding globulins (that bind to estradiol and testosterone), thyroxine-binding globulin etc

6) buffering:
- form important buffering system - protein buffers. helps in acid base balance of the body

7) labile protein store
- serve as mobile protein reserve of the body which can be utilised for tissue growth, especially in situations of protein depletion

8) synthetic function: provide substrate for the synthesis of protein hormones lile erythropoietin etc and for syn of hb

9) determination of ESR - mostly depends on conc of fibrinogen
- fibrinogen facilitates rouleux formation which inturn inc the esr of red blood cells