White blood cells can be mainly divided into two types.
Granulocytes or granules and Agranulocytes or agranulocytes
Granulocytes
White blood cells whose cytoplasm is granular are called granulocytes. The granules are stained with Leishman stain. Its nucleus is 2-7 segmented. 72% of white blood cells are granulocytes. Their lifespan is 4-8 hours. They arise from the myeloblast cells of the bone marrow. Based on the dye holding capacity and the structure of the nucleus, they can be divided into three groups.
1. Neutrophil
The cytoplasm of neutrophils is neutral in color and granular. They are spherical and the nucleus is 2-5 lobed. Their diameter is 12-15 µm. Their number is 4900 per cubic milliliter. That is the highest which is 70%. Lifespan 2-5 days. It is produced in red bone marrow. They exhibit amoeboid motility and enter the site of infection through pores in the cellular network. This process is called diapedesis. They destroy microbes by the process of phagocytosis.
Function of neutrophils
(i) They send chemical messages about microbes
(ii) Increases vascular permeability by secreting lipids
(iii) Swallows microbes by the process of phagocytosis
2. Eosinophil
Their cytoplasm is bluish and acidic and the granules stain reddish-orange with eosin dye. They are spherical and the nucleus is 2-3 lobed. Their diameter is 12-17 µm. Their number is 150-400 per cubic milliliter. That is 1.5% of white blood cells. Lifespan 8-12 days. It is produced in red bone marrow. They are more common in the alimentary canal.
Function of eosinophils
(i) They secrete larvicidal polypeptides and destroy worm larvae
(ii) It destroys allergic antibodies.
(iii) Swallows microbes by the process of phagocytosis
(iv) Secretes hydrolytic enzymes.
(iv) Schistosoma and Trichinella cause death of parasites.
3. Basophil
Their cytoplasm is alkaline and the granules are stained bluish-black. They are round, nucleus is kidney shaped and bilobed. Their diameter is 12-15 µm. Their number is 35 per cubic milliliter. That is the lowest which is 0.5%. Life expectancy is 12-15 days. It is produced in red bone marrow.
The function of basophils
(i) Dilates blood vessels by producing histamine.
(ii) Prevents blood clotting by producing heparin.
Agranulocytes
White blood cells whose cytoplasm lacks granules are called agranulocytes. Their nuclei are large, intact and transparent. 28% of white blood cells are agranulocytes. They originate from bone marrow and lymphoid tissue. They can be divided into two categories.
1. Lymphocytes
Lymphocytes are small in size, round and have large nuclei. It is alkaline and alkaline. Its diameter is 6-16 µm. Their number is 1680 per cubic milliliter. 24% of white blood cells are lymphocytes. Life expectancy is 7 days. It is produced from red bone marrow, liver, spleen and lymph glands. There are three types of lymphocytes.
(i) B-lymphocytes: B-lymphocytes are derived from thymocytes of the thymus gland.
(ii) T-lymphocytes: T-lymphocytes are derived from hematopoietic progenitor cells of bone marrow.
(iii) NK cells: NK cells are toxic to other cells and are detrimental to immunity.
Function of lymphocytes
(i) Produces antibodies and destroys germs
(ii) Acts as a memory cell
(iii) Attacks the virus directly
(iv) Destroys cancer cells.
2. Monocytes
Monocytes are the largest white blood cells. Its nucleus is kidney-shaped or horseshoe-shaped. Its diameter is 12-20 µm. Their number is 280 per cubic milliliter. 4% of white blood cells are monocytes. Lifespan 2-5 days. It originates from red bone marrow (monoblast cells), liver, spleen and lymph nodes. 30-40 hours after generation it transforms into macrophage.
The function of monocytes
(i) Acts as a natural drain
(ii) Ingests viruses and bacteria
(iii) causes phagocytosis.