Why is blood needed by all the parts of a body?

Blood is a specialized body fluid. It has four main components: plasma, red blood cells, white blood cells, and platelets. About 7 to 8 per cent of your total body weight is blood. An average-sized man has about 12 pints of blood in his body, and an average-sized woman has about nine pints.

Blood is needed by all the parts of the body because:

  • It carries oxygen to all the body parts and carries carbon dioxide back to the lungs.
  • It carries digested food to various parts of the body for absorption.
  • It contains platelets that help in the clotting of blood.
  • It helps in maintaining constant body temperature.
  •  It transports hormones and helps in fighting the body with germs and bacteria.


Plasma is the liquid component of the blood, a mixture of water, sugar, fat, protein, and salts. The function of plasma is to transport blood cells throughout your body and nutrients, waste products, antibodies, clotting proteins, a chemical messenger.

Red Blood Cells (also called erythrocytes or RBCs)

Red cells are the most abundant cell in the blood, accounting for about 40 to 45 per cent of their volume. The shape of a red blood cell is a biconcave disk with a flattened centre – in other words, both faces of the disc have shallow bowl-like indentations (a red blood cell looks like a doughnut).

White Blood Cells (also called leukocytes)

White blood cells protect the body from infection. The most common type of white blood cell is the neutrophil. The other major type of white blood cell is a lymphocyte. There are two main populations of these cells. T lymphocytes help regulate the function of other immune cells and directly attack various infected cells and tumours. B lymphocytes make antibodies, which are proteins that specifically target bacteria, viruses, and other foreign materials.

Platelets (also called thrombocytes)

Platelets help the blood clotting process (or coagulation) by gathering at the site of an injury, sticking to the lining of the injured blood vessel, and forming a platform on which blood coagulation can occur.

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