Composition of Blood and their Important Functions in Detail

Blood is the liquid connective tissue and is part of the circulatory system of the body. This blood acts as a transport medium and performs many essential activities.

The blood components can be broadly classified into a

  • The cellular fraction, which makes 45 % and
  • Plasma comprises 55%.

Composition of Blood

1.Blood cells

a) Red blood cells

b) White blood cells

c) Platelets or thrombocytes


Blood cells

This portion forms 40% of the total blood. It has formed elements called cells. These cells are all formed in the bone marrow and released into the bloodstream.

Red blood cells

These cells are called red blood corpuscles or erythrocytes. The blood is red in color due to the presence of these cells in large concentrations. They have hemoglobin in their matrix and helps in carrying oxygen from the lungs to the tissues.

Composition of Blood - Blood cells

White blood cells

These cells are white in color and are of five types:

  1. Neutrophils
  2. Acidophils
  3. Basophils
  4. Monocytes and
  5. lymphocytes.

These white blood cells help to combat infections and help prevent infectious diseases. For more details, refer to types of white blood cells.


These cells are also called platelets. These cells are involved in hemostasis.


This is the clear, straw-colored fluid portion of the blood. It makes up 55% of the blood volume. It has up to 90% of water and 10% of soluble and suspended materials. The solid material includes

  1. Proteins like albumin and globulin.
  2. Nutrients
  3. Gases (Oxygen, carbon dioxide)
  4. Waste material
  5. Lipids
  6. Electrolytes like Na+, Ca+
  7. Hormones
  8. Enzymes


Plasma proteins constitute 7% of the plasma volume. These include serum albumin, globulin and immunoglobulins. These proteins are large and hence unfiltered through capillaries. Hence, these proteins contribute to the osmotic pressure of the blood. Due to this osmotic pressure, the blood stays within the blood vessels.

Albumin, fibrinogen contributes to blood viscosity. This albumin constitutes 60% of total plasma proteins and acts as carrier molecules for free fatty acids, steroidal hormones and drugs.

Goblins have diverse roles, like immunoglobulins provide immunity against microbes and foreign antigens. While thyroglobulin carries thyroxine hormone and transferrin carries iron.

Fibrinogen is a major clotting factor and helps in the coagulation of blood. They prevent the formation of blood clots in the circulation, leading to the blockage of small vessels.


Blood carries nutrients like glucose, amino acids, fatty acids from the digestive system to other tissues. Glucose is meant for energy generation in the form of ATP. Amino acids are used as building blocks for protein synthesis.

Gases (Oxygen, carbon dioxide)

Oxygen and carbon dioxide gases are present in the plasma. Oxygen is supplied from the lungs to the tissue. CO2 is carried from tissues to the lungs for expiration.

Waste material

Waste material is carried from the tissues to the kidney for excretion. These include urea, uric acid, ammonia, etc.


Lipids like HDL, LDL, VLDL are present in the blood.


Plasma has many electrolytes like Na+, Ca2,+ K+, PO4-. These help in the proper transmission of nerve impulses maintain the pH of the blood by acid-base balance. The blood pH is slightly alkaline and is around 7.35 to 7.45.


Hormones are substances released from the endocrine glands. These are carried away to the tissue.

Enzymes SGPT, SGOT, etc., are present in the plasma.

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