White Blood Cells

White Blood Cells (WBCs)

  • White Blood Cells (WBCs), also known as Leukocytes. 
  • WBCs are colorless cells, lacking hemoglobin, and are nucleated. 
  • They are relatively fewer in number compared to red blood cells, averaging between 6000 to 8000 per mm³ of blood. 
  •  WBCs are generally short-lived cells.


Classification of WBCs:


WBCs are classified into two main categories based on their structure: granulocytes and agranulocytes.




  • Granulocytes contain granules in their cytoplasm, visible under a microscope. 
  • The three types of granulocytes are neutrophils, eosinophils, and basophils. 

1. Neutrophils:

  • Neutrophils are the most abundant type of WBC, comprising 60-65% of the total WBC count. 
  • Function: Neutrophils are phagocytic cells, meaning they engulf and destroy foreign organisms entering the body, such as bacteria and fungi. They play a crucial role in the body's innate immune response against infections. 

2. Eosinophils:

  • Eosinophils make up about 2-3% of the total WBC count. 
  • Function: Eosinophils are involved in resisting infections and are associated with allergic reactions. They help combat parasitic infections and modulate allergic responses by releasing chemical mediators. 

3. Basophils:

  • Basophils are the least abundant type of WBC, comprising only 0.5-1% of the total WBC count.
  • Function: Basophils secrete substances such as histamine, serotonin, and heparin, which are involved in inflammatory reactions and allergic responses. They play a role in the body's defense against pathogens and contribute to the inflammatory response.



  •  Agranulocytes lack visible granules in their cytoplasm. 
  • The two types of agranulocytes are lymphocytes and monocytes.


1. Lymphocytes:

  • Lymphocytes make up approximately 20-25% of the total WBC count. 
  • Function: Lymphocytes are responsible for specific immune responses and play a crucial role in adaptive immunity. They include B cells, which produce antibodies, and T cells, which directly attack infected or abnormal cells.


2. Monocytes:

  • Monocytes account for about 6-8% of the total WBC count. 
  • Function: Monocytes are phagocytic cells involved in engulfing and destroying pathogens and cellular debris. They play a role in the body's immune response and contribute to tissue repair and inflammation.


Platelets, also known as Thrombocytes:

  • Platelets are small, disc-shaped cell fragments produced from megakaryocytes, which are specialized cells found in the bone marrow. 
  • Blood typically contains between 150,000 to 350,000 platelets per mm³. 
  • Platelets play a crucial role in blood clotting, also known as coagulation or hemostasis. 
  • When blood vessels are damaged, platelets adhere to the site of injury and aggregate to form a plug, preventing excessive bleeding. 
  • Platelets release a variety of substances, most of which are involved in the coagulation process. These substances include clotting factors, enzymes, and chemicals that promote clot formation. 
  • Clotting factors interact with platelets and other blood components to form fibrin, a protein network that stabilizes the clot and prevents further blood loss. 
  • Platelets also release growth factors that stimulate the repair and regeneration of damaged blood vessel walls, contributing to the healing process. 
  • Platelets are essential for maintaining hemostasis and preventing excessive bleeding. 
  • A reduction in platelet count, known as thrombocytopenia, can lead to clotting disorders, increasing the risk of excessive bleeding and hemorrhage. 
  • Platelet disorders or abnormalities can result in impaired clot formation, leading to prolonged bleeding times and increased vulnerability to injuries and bleeding disorders.