White blood cells (leukocytes) are the colourless and nucleated formed elements of the blood involved in the defense mechanisms of the body
| Cell | Cells/µL (average) | approx. normal range | % of total WBCs | |
|---|---|---|---|---|
| Total WBCs | 9,000 | 4,000-11,000 | … | |
| Granulocytes Neutrophils | 5,400 | 3,000-6,000 | 50-70 | |
| Eosinophils | 275 | 150-300 | 1-4 | |
| Basophils | 35 | 0-100 | 0.4 | |
| Agranulocytes Monocytes | 540 | 300-600 | 2-8 | |
| Lymphocytes | 2,750 | 1,500-4,000 | 20-40 |
Leukocytes can be classified based on the presence or absence of granules in their cytoplasm into the following groups; Granulocytes: granules present; Neutrophils (most abundant)
12-14µm in diameter Motile and actively phagocytic Multilobed nucleus (1-6 lobes)
Young cells have single horse shoe shaped nucleus which becomes multilobed as the cells grow older (lobes are connected with one another by chromatin threads)
Cytoplasm contains neutral stained granules Neutrophils contain defensins, NADPH oxidase, myeloperoxidase, defensins
& thromboxanes Average lifespan in circulation is 6 hours
Functions: Phagocytosis of invading organisms Eosinophils 12-14µm in diameter Less mobile than neutrophils but also phagocytic Usually (85%) bilobed. Lobes are connected with one another by chromatin threads producing a spectacle appearance Cytoplasm contains granules which stain bright brick red with acidic
(eosin) dye Granules contain oxidases, peroxidases and phosphatases, lysozymes &
Major Basic Protein (MBP)
Functions: Detoxification of foreign proteins and other harmful substances Basophils 10-12µm in diameter Irregular bilobed nucleus (often ‘S’ shaped, without clear boundaries due to overcrowding of coarse granules)
Cytoplasm is slightly basophilic (granules stain blue with basic methylene blue)
Granules contain heparin, histamine and serotonin(5HT)
Functions: Allergic reactions Mast cells Heavily granulated wandering cells found in areas rich in connective tissue and are abundant beneath epithelial surfaces Contains heparin, histamine and many proteases They have IgE receptors on their cell membrane Like basophils, they degranulate when IgE-coated antigens bind to their surfaces They are involved in inflammatory responses initiated by IgE & IgG
immunoglobulins
Functions: Innate immunity Agranulocytes: granules absent; Monocytes Largest WBC (18-20µm in diameter) Large single nucleus which is eccentric in position (pushed to one side of the cell)
Nucleus is notched/indented (kidney shaped) It has reticulated chromatin network Cytoplasm is abundant, pale blue, with no granules (sometimes, they contain fine purple dust-like granules called Azur granules)
Functions: Form tissue macrophages which also phagocytize invading organisms MONOCYTES
↙ ↘
↙IN TISSUES WANDERING
Kupffer cells Goes to the site of inflammation Alveolar macrophages Microglia Lymphocytes – Play crucial role in acquired immunity and are classified in two different classifications Morphologically Small lymphocytes (7-10µm in diameter) – rounded nucleus with just the rim of cytoplasm seen Large lymphocytes (10-14µm in diameter) – nucleus is big with indentation. Definite cytoplasm is seen and they are precursors of small lymphocytes Functionally B-lymphocytes – provide humoral immunity (differentiate into plasma cells which further produce 5 classes of antibodies that provide immunity)
T-lymphocytes – provide cell-mediated immunity (T-cytotoxic cells aim to eliminate virus-infected cells, cancer cells and also cause graft rejection)
Physiological variations o Age: more in infants and children o Sex: slightly more in males than in females o Diurnal variation: minimum early in the morning, maximum in the afternoon o Exercise: increases slightly o Sleep: decreases o Emotional conditions like anxiety: increases o Pregnancy: increases o Menstruation: increases o Parturition: increases Pathological variations o Leukocytosis – increase in total leukocyte count (seen in allergy, common cold, tuberculosis, glandular fever, etc.)
o Leukopaenia – decrease in total leukocyte count (seen in anaphylactic shock, viral infections, liver cirrhosis, typhoid and paratyphoid infections, etc.)
o Granulocytosis – abnormal increase in granulocyte number (Neutrophilia, eosinophilia, Basophilia)
o Granulocytopaenia – abnormal decrease in granulocyte number (neutropaenia, Eosinopaenia, basopaenia)
o Agranulocytosis – abnormal increase in granulocyte number (Monocytosis, lymphocytosis)
o Agranulocytopaenia – acute pathological condition characterized by absolute lack of agranulocytes (Monocytopaenia, lymphocytopaenia)
Leukemia – cancerous increase in leucocyte count Myelogenous leukemia Lymphocytic leukemia Leukopaenia – bone marrow produces very few WBCs leaving the body unprotected against bacteria and other invading agents. Can be caused by; Irradiation of the body by x-rays or gamma rays (likely to cause bone marrow aplasia)
Exposure to drugs and chemicals that contain benzene or anthracene nuclei
(also causes bone marrow aplasia)
