What are plasma proteins? Describe the origin, properties and function of plasma protein?

What are plasma proteins?

Plasma proteins are the major solid constituent of the plasma. About 7% of the volume of plasma- nearly all that is not water -is made of proteins.

7.4g/dl(ranges from 6.4-8.3g/dl) is the total plasma protein concentration in the blood. The important fractions of plasma proteins are :

Albumin (4.8g/dl)

Globulins(2.3g/dl) include:

Alpha 1(α1) globulin

Alpha2 (α2)globulin

Beta (β)globulin

Gamma(γ)globulin

Fibrinogen (0.3g/dl).

⏹️Origin of plasma proteins:

There is present various sites in the human body for the formation of plasma proteins,

1. In embryo:

In embryonic stage from the mesenchyme cells the plasma ,proteins are synthesized.The albumin is synthesized first and other proteins are synthesized later.

2. In adults:

In adults the plasma proteins are synthesized mainly from the reticuloendothelial cells of the liver.

In this period the plasma proteins are also synthesized from spleen(largest lymphoid organ of the body),bone marrow, disintegrating blood cells and general tissue cells. Gamma globulin is synthesized from B lymphocytes.

Plasma protein in details

⏹️Properties of plasma proteins:

1.Molecular weight of the plasma proteins:

Plasma proteins are large molecules with the following molecular weight:

Molecular weight of albumin is 69000,

Molecular weight of globulin is ,from 90000-156000,and Molecular weight of Fibrinogen is 500000.

Thus the molecular weight of fibrinogen is greater than that of albumin and globulin.

2.Specific Gravity of plasma proteins:

Specific gravity of the plasma protein is 1.026.

3. Oncotic pressure of plasma proteins:

Plasma proteins are responsible for the oncotic or osmotic pressure in the blood.Osmotic pressure exerted by proteins in the blood is known as colloidal osmotic pressure. Normally the value of it, is about 25mmHg.

4. Amphoteric nature of plasma proteins:

In the plasma proteins NH2 and COOH groups are present. Because of the presence of these groups plasma proteins are amphoteric in nature.

By virtue of their amphoteric nature ,the plasma proteins act as efficient buffers.

5. Electrophoretic mobility of plasma proteins:

In acidic solutions, plasma proteins act as cations and in the alkaline solution plasma proteins act as anions.

6. Water solubility of plasma proteins:

In the plasma proteins because of the presence of polar residues like NH2 and COOH ,they are soluble in water.

⏺️Functions of plasma proteins:

1.Role plasma proteins in the coagulation of blood:

Coagulation of blood is a process in which blood losses its fluidity and becomes a jelly like mass few minutes after it is shed out or collected in a container.

In the coagulation of blood fibrinogen, prothrombin,and other coagulation proteins has an important role.

2.Role of plasma proteins in transport mechanism:

Plasma proteins are involves in the transport mechanism of various substances in the blood . Albumin ,alpha and beta globulin are involves in the transport of hormones and enzymes.

The alpha and beta globulin are also involves in the transport of metals in the blood .

3.Role of plasma proteins in viscosity of blood :

Blood is viscous in nature because of the presence of plasma proteins in it . Albumin provides maximum viscosity than the other plasma proteins.

4. Role as reserve proteins:

Plasma proteins serve as reserve proteins and are utilized by the body tissues during conditions like : fasting , Inadequate protein intake and excessive catabolism of body proteins.

5. Role in maintenance of osmotic pressure in blood:

In the blood, plasma proteins exert colloidal osmotic(oncotic) pressure of about 25mm Hg. Albumin has the greater role in the colloidal osmotic pressure.

6. Role in regulation of acid-base balance:

In the regulation of acid-base balance of the blood plasma proteins especially albumin has an important role. 15% of the buffering capacity of the blood is due to the presence of plasma proteins.

7.Role in Suspension Stability of Red Blood Cells:

Suspension stability refers to the property of the red blood cells by virtue of which they remain uniformly suspended in the blood. Globulins and fibrinogen accelerate this property.

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