What are the various types of leucocytes?

What are the various types of leucocytes?

Leucocytes:

Leucocytes are commonly called White Blood Corpuscles (WBC). These cells lack haemoglobin and are generally far less in num­ber when compared with RBCs. A cubic millimeter of blood contains between 5 to 10 thousand WBCs.

In abnormal conditions the number may increase or decrease. Unlike RBCs WBCs are nucleated and are irregular in shape. The cytoplasm has the organelles like mitochondria, golgi bodies etc., Leucocytes are formed by the process known as leucopoiesis. It takes place in lymph nodes, spleen, thymus and red bone marrow. The Leucocytes have a life span of three to four days. The worn out ones are destroyed in blood liver and lymph nodes.

Classification of WBCs:

Basically there are two types- namely agranulocytes and granulocytes.

(i) Agranulocytes:

These do not have any granules in cytoplasm or oc^ casionally small granules may be found. The cells have a single nucleus and are generally rounded in shape. They are produced in Lymphoid tis­sues. There are two types of agranulocytes viz, monocytes and lympho­cytes.

a. Lymphocytes:

These cells are larger than RBCs. They have a large spherical nucleus and thin cytoplasm. They are non motile and also nonphagocytic. They are produced in lymphnodes and secrete antibodies which destroy invading microbes. The lymphocytes are about 1300 to 3000 in number per cubic milimeter of blood.

b. Monocytes:

These are the largest of all leucocytes and have a large bin shaped nucleus. They are motile. They come out of the blood vessels and engulf bacteria and other cellular debris.

(ii) Granulocytes:

These leucocytes have a number of granules in the cytoplasm and have a distinctly lobed nucleus. The Granulocytes are produced in the red bone marrow. They are also motile and squeeze out of the blood vessels and destroy invading cells. Three kinds of granulocytes have been identified based on their staining reaction. These are basophils, eosinophils and neutrophils.

a. Basophils:

These react positively to the basic stains. They are fairly large in size, have a S shaped nucleus and a few coarse granules. A cubic milimeter of blood consists of about 50 cells averaging to 0.4%. The Basophils release the anticoagulant substance.

b. Eosinophils:

These leucocytes take up acidic stains like eosin appear­ing red in colour. They are fairly large, have bilobed nucleus and abun­dant coarse granules. On an average a cubic milimeter of blood consists of about 60 to 100 cells. Eosinophils destroy toxic substances produced by microbes. In case of infections and allergic reactions the number of eosinophils increases and this condition is called eosinophilia.

c. Neutrophils:

These exhibit a neutral response to both acidic and basic dyes and stain equally well. These are large, have a manylobed nucleus and manyfine granules in the cytoplasm. They are phagocytic in action.