Plasma: The Liquid Part of Blood

Plasma is the liquid portion of blood, constituting about 55% by volume of blood in a normal person, with the cells forming about 45% by volume of the blood. It is composed of approximately 90% water and 10% dissolved substances, including proteins, salts, nutrients, and wastes. The concentration of these substances in plasma varies depending on the condition of the organism and the portion of the system being examined.

 

Types of Solutes in Plasma

There are six types of solutes present in plasma:

Plasma Proteins: 7 to 9% of the plasma is made up of various types of proteins that are synthesized in the liver. These plasma proteins serve important functions in the body, including:

a) Fibrinogen, which plays a role in the clotting process. Prothrombin, a protein, acts as a catalyst in blood clotting. Plasma without fibrinogen is called serum.

b) Immunoglobulins or antibodies, which are produced by lymphocyte cells in response to antigens and are then passed to plasma and lymph. Immunoglobulins play a critical role in the body's defense against diseases.

c) Maintaining osmotic pressure between the blood stream and surrounding medium, as water does not readily pass through the walls of blood vessels due to the large size of plasma proteins.

Inorganic or Mineral Ions: Salts make up about 0.9% of human plasma, with sodium chloride and bicarbonates comprising over two-thirds of this amount. Trace amounts of calcium, magnesium, copper, potassium, zinc, and other metabolic ions are also present. Shifts in the concentration of these ions can cause significant disturbances in the body.

Organic Nutrients: Plasma also contains organic nutrients such as glucose, fats, phospholipids, amino acids, and lactic acids.

Metabolites and Wastes: Amino acids, glucose, vitamins, lipids, urea, and uric acids are among the metabolic waste products present in plasma.

Hormones: Plasma serves as a carrier for various hormones that are transported throughout the body.

Dissolved Gases: Carbon dioxide (CO₂), oxygen (O₂), and nitrogen (N₂) are also present in plasma.