BRIEF ACCOUNT ON BLOOD PLASMA AND ITS FUNCTIONS

Blood:

The blood is the medium in which dissolved nutrients, gases, hormones and wastes are transported through the body. It is made up of two main components.

• The Plasma
• Cells or Cell-like bodies (white blood cells, red blood cells, and platelets)

The weight of the blood in our body is about 1/12^th of the body, means that if a person weighs about 60Kg, then 1/12^th of it, about 5kg is the blood. This remarkable fluid is all (i.e. 5 to 6 liters) the time being circulated throughout the body day and night for whole life.

Little Experiment to Separate Blood Plasma and Cell like Bodies:

Separation of Plasma from Blood

It is a common observation, that when blood is outside our body or the body of other animals, it coagulates or clots. If we put blood with an anticoagulant such sodium citrate in a test tube; and allow it to stand, then after sometime we can see that blood separates into two layers. The upper layer is pale yellow in color while second layer (the lower layer) is brick red in color. This pale yellow upper part is the plasma — the liquid portion of the blood; and the lower brick red contains cell like bodies like white blood cells, red blood cells and platelets.

Plasma:

Blood Plasma is the pale yellow portion of the blood in which blood cells and platelets are usually suspended. 

A Plasma Cell

Composition:

In normal person, plasma constitutes about 55% by volume of the blood, plasma is primarily water in which proteins, salts and nutrients are dissolved. Water constitutes about 90% of plasma, 10% are dissolved substances.

Ions	Normal Concentration Range
Sodium	135-145 mmol/L
Potassium	3.5-5.1 mmol/L
Chloride	95-105 mmol/L
Calcium	2.1-2.5 mmol/L

The substances dissolved or present in plasma vary in their concentration with the condition of the organism and with the portion of the system under examination. The solutes can be divided into six categories:

• Inorganic salts (ions)
• Plasma proteins
• Organic nutrients
• Nitrogenous waste products
• Hormones
• Gases which are dissolved

Inorganic Ions or Mineral Ions:

Together the inorganic ions and salts make 0.9 percent of the plasma, of humans, by weight; more than two third of this amount is sodium chloride, the ordinary table salt.

Even if the total concentrations of dissolved substances remain the same, shifts in the concentration of particular ion can create serious disturbances.

They help to regulate osmotic pressure of the blood. They are also important to control pH of the blood, as HCO₃ and H₂PO₄ act as buffers and these allow the blood plasma to absorb H⁺ ions, without effectively increasing its pH. The normal pH of human blood is 7.4 and it is maintained within narrow limits, because the change in pH would affect the chemical reactions of the body.

The Plasma Proteins:

Plasma proteins constitute 7-9 percent by weight of the plasma. Most of these proteins which are of many types are synthesized in the liver. These proteins perform many functions:

Defense against Disease:

Production of Antibodies in response to Antigen

Some of the globulins, called immunoglobulin or antibodies, are produced in response to antigens, by lymphocytes (B and T) cells; and then are passed to plasma, and lymph. Immunoglobulin play important role in body's defense against diseases.

Maintain Viscosity:

The proteins in the plasma, also maintain viscosity of the blood only if the viscosity (viscosity is a measure of internal friction of a fluid i.e. the friction between molecules as they slide pass each other) of the blood is nearly normal.

Facilitate Transport of Materials:

Plasma proteins bind to certain hormones, (α-globulin) fatty acids, and other lipids, some vitamins, and various materials; they greatly facilitate the transport of such substances by the blood (β-globulin).

Clotting of Blood:

Prothrombin acts as a catalyst in blood clotting process. Fibrinogen takes part in the blood clotting process.

Organic Nutrients:

Organic nutrients include glucose, fats, phospholipids, amino acids and lactic acids. Some of them enter the blood from the intestine (during absorption). Lactic acid is produced in muscles as a result of Glycolysis, and is transported by blood to liver where it is oxidized to release energy. Most of it is converted into glycogen. Cholesterol is an important constituent, which is metabolized to some extent, but also serves as precursor of steroid hormones.

Nitrogenous Waste Products:

Nitrogenous waste products are formed as a result of cellular metabolism. These products are carried from the liver where they are produced, to the organs from where they are removed i.e. kidneys. Urea and small amounts of uric acid are present in plasma.

Hormones:

All the hormones in the body are carried by blood – so they are present in the plasma.

Gases:

The gases such as O₂, CO₂, are present in the plasma of the blood.