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.