Describe the various types of blood cells and their functions.

Blood consists of liquid medium called plasma. It contains several salts, glucose, aminoacids, proteins, hormones, digested and excretory products. Serum is blood plasma from which the blood clotting protein-fibrinogen is removed. In the plasma of blood the following three components are found:
(i) Red blood cells or erythrocytes.
(ii) White blood cells or leucocytes.
(iii) Thrombocyte (platelets).
(i) Red blood cells or spherical, disc shaped. Human RBC’s are biconcave and are devoid of nucleus. Their number is about 5 million per cubic mm of blood. Their red colour is due to the presence of a pigment haemoglobin. Main function of RBC’s is to transport oxygen with the help of haemoglobin.

(ii) White blood cells or leucocytes do not have a definite shape and possess a nucleus. These are bigger than RBC’s and are of five types. Main function of leucocytes is to protect the body from micro-organisms and provide immunity to body.
(iii) Blood platelets or thrombocytes are small bodies numbering about 5,00,000 per cubic mm of blood. They perform an important function of forming a clot on the skin in the event of an injury and thus prevent excess flow of blood from the body.

 Human blood cell