Blood plasma: composition and function

Blood plasma is a viscous homogeneous liquid of light yellow color. It is about 55-60% of the total blood volume. In the form of suspension in it are blood cells. Usually the plasma is transparent, but after eating fatty foods it can be slightly cloudy. It consists of water and mineral and organic elements dissolved in it.

Composition of plasma and the function of its elements

The bulk of the plasma is water, its amount is about 92% of the total volume. In addition to water, it includes the following substances:

  • proteins;
  • glucose;
  • amino acids;
  • fat and fat-like substances;
  • hormones;
  • enzymes;
  • minerals( ions of chlorine, sodium).

About 8% of the volume is made up of proteins, which are the main part of the plasma. It contains several types of proteins, the main ones are:

  • albumins - 4-5%;
  • globulins - about 3%;
  • fibrinogen( refers to globulins) - about 0.4%.


Albumin is the main plasma protein. It has a low molecular weight. The plasma content is more than 50% of all proteins. Albumins are formed in the liver.

Protein functions:

  • perform transport function - transfer fatty acids, hormones, ions, bilirubin, drugs;
  • take part in the metabolism;
  • regulates the oncotic pressure;
  • are involved in the synthesis of proteins;
  • reserve amino acids;
  • deliver medicines.
A change in the level of this protein in plasma is an additional diagnostic feature. The albumin concentration is determined by the concentration of albumin, since for many chronic diseases of this organ it is characteristic to reduce it.


The remaining plasma proteins are globulins that are large molecular. They are produced in the liver and in the organs of the immune system. The main types:

  • alpha globulins,
  • beta globulins,
  • gamma globulins.

Alpha-globulin binds bilirubin and thyroxin, activates the production of proteins, transports hormones, lipids, vitamins, trace elements.

Beta-globulins bind cholesterol, iron, vitamins, transport steroid hormones, phospholipids, sterols, cations of zinc, iron.

Gamma-globulin binds histamine and is involved in immunological reactions, therefore they are called antibodies, or immunoglobulins. There are five classes of immunoglobulins: IgG, IgM, IgA, IgD, IgE.They are produced in the spleen, liver, lymph nodes, bone marrow. They differ from each other in biological properties, structure. They have different ability to bind antigens, activate immune proteins, have different avidity( antigen binding speed and strength) and the ability to pass through the placenta. Approximately 80% of all immunoglobulins leave IgG, which have high avidity and are the only one that can penetrate the placenta. The fetuses are the first to synthesize IgM.They also appear first in the serum after most vaccinations. They have high avidity.

Composition of blood
Composition of blood

Fibrinogen is a soluble protein that forms in the liver. Under the influence of thrombin, it turns into insoluble fibrin, due to which a blood clot forms at the site of damage to the vessel.

Other proteins

In addition to the above, the plasma contains other proteins:

  • complement( immune proteins);
  • transferrin;
  • thyroxine-binding globulin;
  • prothrombin;
  • C-reactive protein;
  • Haptoglobin.
Also you can read: Laboratory test tubes for the determination of total protein Total protein in the blood

Nonprotein components

In addition, the blood plasma includes non-protein substances:

  • organic nitrogen containing: amino acid nitrogen, urea nitrogen, low molecular weight peptides, creatine, creatinine, indikan. Bilirubin;
  • organic nitrogen-free: carbohydrates, lipids, glucose, lactate, cholesterol, ketones, pyruvic acid, minerals;
  • inorganic: cations of sodium, calcium, magnesium, potassium, anions of chlorine, iodine.

The ions in the plasma regulate the pH balance, the cells state normally.

Protein Functions

Proteins have several uses:

  • homeostasis;
  • ensuring the stability of the immune system;
  • maintenance of the aggregate state of blood;
  • nutrient transfer;
  • involved in the process of blood clotting.

Plasma functions

Blood plasma performs many functions, among which:

  • transportation of blood cells, nutrients, metabolic products;
  • binding of liquid media that are outside the circulatory system;
  • making contact with body tissues through extravascular fluids, thereby carrying out hemostasis.
Blood donor
Donor plasma saves a lot of human lives

Use of donor plasma

For transfusion in our time, more often than not whole blood is needed, but its components and plasma. Therefore, at points of transfusion, blood is often delivered to the plasma. It is obtained from the whole blood by centrifugation, that is, the liquid part is separated from the shaped elements by the apparatus, after which the blood cells are returned to the donor. The procedure lasts about 40 minutes. The difference from the delivery of whole blood is that the blood loss is much less, and you can return the plasma in two weeks, but no more than 12 times during the year.

Serum of blood is obtained from plasma, which is used for medicinal purposes. It differs from plasma in that it lacks fibrinogen, while it contains all the antibodies that can withstand pathogens. To receive it, sterile blood is placed in the thermostat for an hour. Then exfoliate the formed clot from the wall of the tube and keep it in the refrigerator for a day. After this, with the help of a Pasteur pipette, the whey that is left is drained into a sterile container.


Blood plasma is its liquid component, which has a very complex composition. Plasma performs important functions in the body. In addition, the donor plasma is used for transfusion and the preparation of therapeutic serum, which is used for prevention, treatment of infections, and also for diagnostic purposes to identify the microorganisms obtained during the analysis. It is considered more effective than vaccines. Immunoglobulins, contained in the serum, immediately neutralize harmful microorganisms and products of their vital activity, passive immunity is formed more quickly.