Plasma: What is it? Where is it located? Functions and Transfusions of This Important Liquid Fraction of the Blood

Blood constitutes between 7% and 8% of the bodyweight of a human being.

That equates to up to almost 5.5 liters of blood in an adult. The essential function of the blood is to transport oxygen and nutrients throughout the body.

Put, without blood circulating through our system; we would die instantly. However, the blood performs many more functions apart from these primary functions.

Some of the most important functions of blood include:

  • Eliminate waste products from the body, such as carbon dioxide.
  • The transport of hormones.
  • Regulates acidity levels (pH).
  • Regulates body temperature.

The components of blood can be essentially classified into two categories.

  1. First, solid particles, such as platelets, white blood cells, and red blood cells.
  2. The rest of the blood is made up of blood plasma.

Each of these components carries out a specific function within the blood. All are necessary for the body to function normally.

Where is it located?

Plasma is the pale yellow, aqueous solution that suspends all other parts of the blood.


It constitutes about 55% of the total volume of the blood.

It is a solvent for essential proteins, nutrients, electrolytes, gases, and other substances necessary for life.

Plasma represents the liquid fraction in the blood. And it has a density of 1025 kg / m3.

Plasma comprises 91% water and 9% inorganic components such as sodium, potassium, magnesium, chloride, calcium, bicarbonate (HCO3), and phosphoric acid (HPO4).

Organic components include proteins, hormones, vitamins, lipids, and other organic metabolites such as glucose, amino acids, pigments, enzymes, uric acid, and urea.

Plasma functions

Although it is often thought that plasma is less critical than blood cells that carry oxygen and provide immunity.

Plasma is equally essential as it is responsible for many different functions in the body, such as:

  • Nutrient transport.
  • Waste transportation.
  • Electrolyte balance.
  • Maintain blood volume.
  • Defense of the organism.

Nutrient transport

One of the most critical functions of plasma is transporting nutrients throughout the body.

This includes amino acids (the building blocks of proteins), lipids (fats), sugars (glucose), and fatty acids.

These nutrients are distributed to cells throughout the body, where they are used to maintain healthy functions and growth.

Research has shown that more than 500 different proteins have been found in plasma to date.

Plasma is believed to contain part of every type of protein that the human body can make.

Another protein synthesized by the liver, serum albumin, constitutes approximately 60 percent of all plasma proteins.

Other proteins called alpha and beta globulins to carry lipids such as cholesterol and steroid hormones, sugar, and iron.

This carrier substance is essential for various substances, including hormones.

The endocrine system also secretes hormones such as insulin, corticosteroids, and thyroxine into the blood.

Plasma hormone concentrations must be carefully regulated for good health and transported by plasma throughout the body.

Waste transportation

In addition to transporting nutrients, plasma transports waste products such as uric acid, creatinine, and ammonium salts, from the body’s cells to the kidneys.

The kidneys filter these wastes from the plasma and excrete them from the body in the form of urine.

These nitrogenous wastes must be excreted since if they increase significantly, they can cause kidney failure.

Electrolyte balance

Electrolytes and the acid-base system found in plasma are finely regulated.

For example, potassium usually is present in plasma at a concentration of only four milliequivalents per liter.

A slight increase in plasma potassium (to 6-7 milliequivalents per liter) can cause death.

Similarly, plasma sodium, chloride, bicarbonate, calcium, and magnesium levels must be kept precisely within a narrow range.

The smallest molecules such as sodium, potassium, glucose, and calcium are mainly responsible for the concentration of dissolved particles in plasma.

Plasma carries these electrolytes throughout the body. These salts are essential for many bodily functions.

Without these salts, the muscles would not contract, and the nerves would not be able to send signals to and from the brain.

Maintain blood volume

Albumin is one of the proteins created by the liver.

Albumin helps keep the plasma contained within blood vessels.

In patients with renal dysfunction or low plasma protein concentrations, especially when albumin levels are low, the plasma can develop a migration of water from the vascular space to the tissue spaces.

Entering the tissue can cause edema (swelling) and congestion in the limbs and vital organs, including the lungs.

Albumin is also present in the cells’ fluids, known as interstitial fluid.

The albumin concentration in this fluid is lower than in plasma. Because of this, water cannot pass from the interstitial fluid into the blood.

If the plasma did not contain as much albumin, the water would pass into the blood, increasing blood volume and causing an increase in blood pressure that would make the heart work harder.

The concentration of proteins on both sides of the semipermeable membranes, such as the endothelial cells that line the capillaries, create the crucial pressure gradients necessary to maintain the correct amount of water within the intravascular compartment and therefore to regulate the volume of circulating blood.

Defense of the organism

When blood clotting is activated, the fibrinogen circulating in the blood is converted to fibrin, which helps form a stable blood clot at the site of vascular disruption.

Clotting inhibitor proteins help prevent abnormal clotting (hypercoagulability) and resolve clots after they form.

Substances secreted into plasma by cancers may indicate occult malignancy; for example, a higher prostate-specific antigen concentration in an asymptomatic middle-aged man may indicate undiagnosed prostate cancer.

Gamma globulins, or immunoglobulins, are an essential class of proteins secreted by the B lymphocytes of the immune system.

They include most of the body’s supply of protective antibodies produced in response to specific viral or bacterial antigens.

Cytokines are proteins synthesized by cells of various organs and by cells found in the immune system and bone marrow to maintain normal blood cell formation (hematopoiesis) and regulate inflammation.

For example, a cytokine called erythropoietin, synthesized by specialized cells in the kidney, stimulates blood progenitor cells in the bone marrow to produce red blood cells.

Other cytokines stimulate the production of white blood cells and platelets.

Another protein system in plasma, called complement, is essential for mediating appropriate immune and inflammatory responses to various infectious agents.

About 7 percent of plasma is protein.

The protein found in the highest concentration in plasma is albumin, an essential protein for tissue repair and growth.


Whole blood, which contains red blood cells, plasma, platelets, and clotting factors, is rarely used for transfusions because most transfusions only require specific blood components.

It can be used only up to 35 days after it has been drawn and is not always available because most units of blood collected are used to obtain components.

Plasma is obtained when all blood cells – red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes) – are separated from whole blood.

The remaining yellowish fluid contains 90 to 92 percent water but contains solutes necessary for maintaining health and life.

Plasma, the liquid portion of blood, contains all of the non-cellular components of whole blood, including clotting factors, immunoglobulins, other proteins, and electrolytes.

When frozen, clotting factors remain stable for up to a year but are usually transfused within 24 hours of thawing.

However, some of the clotting factors, such as factor VIII (or antihemophilic factor), and factor V, are very labile even after the plasma is frozen and require stabilizing substances (for example, glycine) or the use of special freezing procedures.

Fresh frozen plasma is used in patients with multiple clotting factor deficiencies, such as those with severe liver disease or massive bleeding.

Cryoprecipitate is prepared from fresh frozen plasma and contains approximately half the original amount of clotting factors, although these factors are highly concentrated in 15-20 milliliters.

Cryoprecipitate is used to treat patients with deficiencies of factor VIII, von Willebrand factor, factor XIII, and fibrinogen.

Specific clotting factor concentrates are prepared from pooled plasma or pooled cryoprecipitate.

Factor VIII concentrate, an antihemophilic factor, is the preferred treatment for hemophilia A. Factor IX complex, prothrombin complex, is also available to treat hemophilia B (factor IX deficiency).


Immunoglobulin, obtained from the plasma of a pool of healthy donors, contains a mixture of immunoglobulins, mainly immunoglobulin G, with smaller amounts of immunoglobulin M and immunoglobulin A.

They are used to provide passive immunity to various diseases such as measles, hepatitis A, and hypogammaglobulinemia.

Intravenous immunoglobulins provide immediate antibody levels and avoid the need for painful intramuscular injections.

Hyperimmune serum globulin is prepared in the same way as the nonspecific immunoglobulin listed above but from patients who are selected for their high specific antibody titers.

Rh immune globulin is given to pregnant Rh-negative women to prevent hemolytic disease of the newborn.

Other hyperimmune serum globulins are used to prevent hepatitis B, tetanus, rabies, and chickenpox or shingles, in exposed people.