WBC Full Form

The full form of WBC is White Blood Cells. It is also known as white blood corpuscle or leucocytes. The blood consists of three types of cellular elements, namely Red blood cell/ erythrocyte, white blood cell (WBC)/leukocyte and platelets/ thrombocytes. But specifically discussing WBCs, the word leucocyte is derived from the Greek word ‘leucko’ (meaning white) and ‘cyte’ (meaning cell). They are known as the defence mechanism of the body as they protect the body from invasion by a foreign body. The white blood cells mount immune reactions in response to any wound or injury. They work by activating humoral and innate immunity. 

LEUCOPOIESIS- DEVELOPMENT OF WBC

The development of WBCs takes place in the bone marrow. They undergo a maturation from a stem cell into a fully mature white blood cell. Granulocytes and agranulocytes have different development mechanisms.

1. Granulopoiesis: 

• occurs for three days. 

• The granulocytes exclusively develop in the red bone marrow. 

• Following is the series of maturation: 

2. Agranulocytes: 

• Chief site of origin is- Lymphoid tissues like lymph nodes, thymus, spleen, tonsils etc.

• Some of them develop in the bone marrow itself.

 TYPES OF WBCs

STRUCTURAL CLASSIFICATION

The structure is visualised by staining with Leishman’s stain.

There are different varieties of leucocytes that circulate in the blood. WBCs are broadly classified into the following based on whether their cytoplasm carries granules or not.

1. Granulocytes: they are the white blood cells with granules present in their cytoplasm.

2. Agranulocytes: as the name suggests, there are no granules in the cytoplasm.

FUNCTIONS OF DIFFERENT WBCs

1. Neutrophil: 

• Phagocytosis: they are also referred to as “First-line defence” because they are the first ones to rescue the cells from an invasion of a foreign body.

• Endogenous pyrogen: it is a fever producing chemical that mediates the febrile response to bacterial pathogens.

2. Eosinophil: 

• Level of phagocytosis is moderate

• They engulf larger parasites that can’t be ingested by mere phagocytosis.

3. Basophil:

• Histamine and Heparin, an anticoagulant is liberated by eosinophil

• Mild level of phagocytosis

4. Lymphocytes:

• Antibody production: B and T lymphocytes

5. Monocytes: 

• Called the “second line of defence”, because after neutrophils they act as the defensive mechanism.

MECHANISM OF PHAGOCYTOSIS 

During phagocytosis, the following chain of events take place.

1. Diapedesis: neutrophils are motile structures. This characteristic helps them to travel across the bloodstream into the tissues. This process is referred to as diapedesis.

2. Chemotaxis: the neutrophils are attracted towards the site of injury by the chemical combination formed by the bacterial products and plasma protein-called agents.

3. Opsonization: the antibodies formed against bacterial pathogens are called Opsonins. They coat the bacteria to make them attract phagocytes. This is called opsonization.

4. Phagocytosis: 

– the coated bacteria bind to membrane receptors of neutrophil. They then get phagocytosed by endocytosis.

– a ph between 6-8 is favourable for phagocytosis to take place.

5. Degranulation: lysozymes and peroxidases are bacterial substances called defensins. They are released after phagocytosis. They kill the bacteria in the digestive pouch (degranulation)

6. Inflammatory response: results from the production of histamines, lysosomal enzymes.

7. Limiting inflammation: prostaglandins (PGs) are substances having an anti-inflammatory effect. Additionally, the release of thromboxanes also limits the inflammatory process.

CLINICAL IMPORTANCE OF WHITE BLOOD CELLS

A clinically relevant test known as the complete blood count (CBC) test measures the count of leukocytes in the blood smear. It helps to provide significant insights into medical conditions. 

CBC are routinely ordered by medical practitioners.

DISORDERS RELATED TO WBC

The imbalance in leucocyte count contributes to various conditions.

1. Leucopenia: a condition when total leucocyte count (TLC) goes less than 4000/ µL

2. Leukocytosis: a condition when total leucocyte count (TLC) goes above 11000/ µL

3. Leukaemia: it is a terminology used to refer to cancer of blood cells. The TLC count goes more than 50000/ µL. 

4. Neutrophilia: a rise in neutrophil count

5. Neutropenia: decreased number of neutrophils

6. Eosinophilia: rise in eosinophil count

7. Eosinopenia: decreased number of eosinophils

8. Basophilia: rise in basophil count

9. Basopenia: decreased number of basophils

10. Lymphocytosis: rise in lymphocyte count

11. Lymphopenia: decreased number of lymphocytes

12. Monocytosis: rise in monocyte count

13. Monocytopenia: decreased number of monocytes

CONCLUSION

The acronym WBC stands for white blood cell. They are crucial for protecting against numerous diseases by increasing the immunity of an individual. The process of formation of leukocytes/ WBCs is called leukopoiesis. They are formed in the bone marrow and then travel in the bloodstream and lymph. There are two broad categories of white blood cells (WBCs) namely granulocytes and agranulocytes. They are further classified into the different arrays of WBC cells. Every variant of WBC performs its crucial function. The disturbance in the equilibrium of the count of white blood cells results in various medical conditions.