There are two types of WBC or Leukocytes. They are:
A. Agranulocyte or Non-Granulocytes and
A. Agranulocyte or Non-Granulocytes: (Gr. a-, not; granulum- granule; L. kytos- cells). In this type of leukocyte the granules are absent.
Types of Agranulocytes:
There are two types of agranulocytes. They are:
i) Lymphocytes and
i) Lymphocytes: (L. lymph, water; Gr. kytos, cell). These cells are formed in lymph glands, thymus, liver, spleen, tonsils, and other lymphoid tissues. They are developed from the lymphoblasts of red bone marrow.
Types of lymphocytes:
The lymphocytes are of two types:
• B-lymphocytes (B cells)
• T-lymphocytes (T cells)
B-lymphocyte: These cells produce antibodies for the neutralisation of antigens.
T-lymphocytes cells: These cells are involved in allergic reactions, graft rejections, tumour control and regulation of immune system.
ii) Monocytes: (Gr. monos, – single; kytos, cells). The monocytes are the largest among all the WBC, with large bean shaped nucleus. They are 4% in total WBC.
They are developed from the monoblasts of bone marrow and come into blood circulation. They are motile, capable of amoeboid movement and phagocytic in nature.
B. Granulocytes: (L. granulum- small grain, Gr. kytos- cell). These cells are characterised by the presence of small granules in their cytoplasm.
The Granulocytes developed from the myeloblasts of the bone marrow. (The myeloblasts are the amoeboid cell stage of bone marrow, which give rise the myelocytes).
The nucleus of the granulocyte is bilobed or multilobed. That’s why these are also known as Polymorphonuclear cell. The main function of these cells is phagocytic. Their life span is about 14 hours.
Types of granulocytes:
Granulocytes are of three types. They are:
ii) Basophils and
iii) the neutrophils.
i) Eosinophils (Acidophils): (Gr. eos- dawn; philein, to love). These cells are spherical with bilobed nucleus. The lobes of the nucleus remains connected with a slender connective giving the shape of a spectacle. The cytoplasmic granules are larger and strain brilliantly with acid dyes e.g. eosin and appear red.
They are 2 to 4% in total number of WBC i.e. their normal count (value) is 2 to 4% in total number of leukocytes, in human blood. The increase in their number in blood is known as eosinophilic. Their number is increased in asthma and parasitic infection. These cells play an important role in detoxification or neutralising the toxins in body.
ii) Basophils: (Gr. basis,‐ base; philein ‐ to love). These are also the spherical cells with ‘S’ shaped nucleus. They have great affinity with basic dyes e.g. methylene blue.
They release histamine, heparin, and serotonin. The histamine dilates the blood vessels and increases the permeabilities of small vessel walls, heparin prevents the blood coagulation and the serotonin acts as a neurotransmitter.
They are less than 1% (about 0.4%) in total WBC count.
iii) Neutrophils: (L. neuter- neither; Gr. philein- to love). These cells are spherical and possess multi-lobed nucleus. The number of lobes are usually three but does not exceed five. The cytoplasm contains fine granules. They don’t have special affinity with any dye. So, they stain weakly with both acid and basic dye and appear in purple colouration.
Their number is largest (60- 70%) among all WBC. They are formed in the bone marrow and their lifespan is 4 to 8 hours in the blood, and 4 to 5 days in the tissue.
The neutrophils are phagocytic in nature. They engulf bacteria and other foreign bodies along with dead cells. They reach in large number to any infected area by amoeboid movements and ingest the microbes by the process of phagocytosis.
The number of neutrophils is increased in several cases such as in strenuous exercise, and in pregnancy.
The dead neutrophils, the dead body cells along with the microbes from the pus.
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