08 Respiration and Circulation - part 10 - White blood corpuscles / Leucocytes

 

08 Respiration and Circulation - part 10 - White blood corpuscles / Leucocytes


White blood corpuscles / Leucocytes:
  • Are colourless, nucleated and amoeboid cells larger than RBCs.
  • Due to their amoeboid movement they can move out of the capillary walls by a process called diapedesis.
  • A normal adult has on an average, 5000-11000 WBCs per mm3 of blood. 
  • Decrease in number of WBCs (<4000) is called leucopenia (common in HIV, AIDS and TB patients or those exposed to radiations, shock, etc). 
  • Temporary increase in number of WBCs is called as leucocytosis. 
  • It is due to infection. It also occurs during pregnancy and in newborn babies. 
  • Uncontrolled increase in number of WBCs is a type of blood cancer called leukemia. 
  • WBCs are mainly concerned with defense mechanism i.e. protection.
Types of WBCs :
  • Colourless, irregular nucleated cells and show polymorphism (exist in variable forms). 
  • They can be classified into two main types such as - 
  1. Granulocytes and 
  2. Agranulocytes.
A. Granulocytes :
  • WBCs with a granular cytoplasm, also called Polymorpho nuclear leucocyte (PMN) cells. 
  • Have lobulated nuclei in different shapes. 
  • Formed from myeloid stem cells and once formed, do not divide. 
  • Constitute about 72% of total WBCs. 
  • Granules are actually secretory vesicles which contain various secretions, enzymes, etc. 
  • Depending upon staining property of the granules, these granulocytes are classified into three types as - 
  1. Neutrophils
  2. Basophils and 
  3. Acidophills.
a. Neutrophils : 
  • Granules are very fine, large in number, evenly distributed and stained with neutral stains (dyes). 
  • Are about 70% of total WBCs. 
  • Are spherical and nucleus is several lobed (2-7). 
  • Able to perform amoeboid movements and phagocytosis. 
  • Responsible for destroying pathogens by the process of phagocytosis. 
  • ‘Pus’ is mixture of dead neutrophils, damaged tissues and dead microbes.
B. Basophils / Cyanophils : 
  • Have very few granules of large size, and stain with basic stains like methylene blue. 
  • Are non-phagocytic, small, spherical cells and are about 0.5-1% of total WBCs.. 
  • Nucleus is twisted. 
  • Present in infected and allergic conditions only. 
  • Secrete heparin, histamine and serotonin.
c. Eosinophils / Acidophills : 
  • Contain lysosomal granules that are stained to red colour with acidic stains like eosin.
  • Eosinophils are about 1 – 3 % of total WBCs.
  • Nucleus is bilobed. 
  • Destroy antigen antibody complex by phagocytosis. 
  • Their number increases in allergic condition and they show antihistaminic property. 
  • Also responsible for detoxification as they produce antitoxins.
B. Agranulocytes :
  • Are about 28% of total WBCs. 
  • Cytoplasm of these leucocytes is without granules. 
  • Formed from lymphoid stem cells and can divide by mitosis. 
  • Nuclei of agranulocytes are large in size but are not lobulated like the granulocytes. 
  • Two types of agranulocytes - 
  1. Lymphocytes and 
  2. Monocytes.
a. Lymphocytes : 
  • Are the smallest of all WBCs.
  • Large spherical nucleus. 
  • They constitute about 25-30% of total WBCs. 
  • Depending upon function, two types of lymphocytes are present as - 
  1. B-lymphocytes and 
  2. T-lymphocytes. 
B-lymphocytes :
  • Mature in bone marrow 
  • Responsible for antibody production/humoral immunity. 
  • It is a highly specific antigen, antibody immunity. 
T-lymphocytes : 
  • Mature in thymus 
  • Responsible for cell-mediated immunity. 
  • Sub types of T-lymphocytes are -
  1. Helper T-cells
  2. Killer T-cell
  3. Memory T-cells and 
  4. Suppressor T-cells
b. Monocytes : 
  • Are the largest of all the WBCs. 
  • Its nucleus is large and bean or kidney shaped. 
  • They form 3-5% of WBCs. 
  • Are actively motile and give rise to macrophages. 
  • They are mainly phagocytic .
  • Destroy the bacteria and dead or damaged tissue by phagocytosis.

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