Question

Give an account on cellular components of blood.

Answer 1

There are three types of blood cells or corpuscles.

(i) Red Blood Corpuscles (RBC or Erthrocytes): These are circular, biconcave and non-nucleated cells. Their main component is a red-pigmented protein, haemoglobin. The haemoglobin transports O${}_2$. They are manufactured in the marrow of bones. They disintegrate in the spleen and liver.

(ii) White Blood Corpuscules (WBC or Leucocytes): They are nucleated cells exhibiting amoeboid movement. They protect the body against invading micro-organisms. There are five types of leucocytes.

(a) Neutrophils: These are the most common type of leucocytes (60-70%) in the blood. Their nuclei can occur in more than one form. Hence they are called polymorphonuclear neutrophils (PMN).

(b) Eosinophils (0.5-3.0%): They are motile cells that leave the circulation to enter the tissues during an inflammatory reaction. During allergy reaction, their number increases.

(c) Basophils(0.1%): They play a role in the allergic and inflammatory reaction. They contain heparin which inhibits blood clotting.

(d) Lymphocytes (20-30%): These are smallest leucocytes. They are more common in lymphatic tissues namely the lymph nodes, spleen tonsils and thymus. Lymphocytes called B-cells can produce proteins called antibodies that can get attached to the bacteria and destroy them. T-cells protect us against viruses by attacking and destroying cells in which viruses are reproducing.

(e) Monocytes (1-4%): These are largest leucocytes. They destroy bacteria, dead cells and cell fragments. During chronic infection, their number increases.

(iii) Blood platelets or Thrombocytes: These are minute fragments of cells that play a very important role in coagulation of blood. Their life expectancy is 5-9 days.