Blood - 2

RBC : They are also called Erythrocytes. They are many in number. They are biconcave and disc-like corpuscles. Their diameter is about 7-8 μm. Their number is about 5.0 million/cubic mm. They do not have nucleus. They do not have mitochondria or endoplasmic reticulum. They are formed in the red bone marrow. Their life span is about 120 days. The spleen is known as the graveyard of RBC. The RBCs contain haemoglobin (Hb) pigment which is a red colored substance. The haemoglobin contains iron. An adult person has about 12-16 g of Hb in 100 ml of blood. RBC also contains carbonic anhydrase.

WBC : They are also called Leucocytes. They are large. They are colourless due to the absence of any pigments. Their number is about 7000/cubic mm. They have a nucleus centrally. Their life span is about 24 hours. Leucocytes are broadly classified into granulocytes and agranulocytes.

Granulocytes: They are the cells with granular cytoplasm and polymorphic nucleus. They are further grouped into 3 categories:

1. Neutrophils : They do not stain with acidic or basic dyes. The nucleus is 5-7 lobed. They are phagocytic and provide protection against infection. They constitute about 62% of leucocytes.
2. Basophils : They are stained by acidic dyes like Eosin. The nucleus is bilobed. They are slightly phagocytic and help in detoxification. They constitute about 2-3 % of leucocytes.
3. Eosinophils : They are stained with basic dyes like Methylene Blue. The nucleus is 2 or 3 lobed. They play an important role in inflammatory reactions. They constitute about 0.5-1% of leucocytes.

Agranulocytes: They are the cells that have no granular cytoplasm. Their nucleus is kidney shaped. Their colour is pale-blue. They are of the following 2 types:

1. Monocytes : They are large cells. Their diameter is about 10-18 μm. Nucleus is kidney shaped. They are phagocytic and motile. They form 6-8% of leucocytes.
2. Lymphocytes: They may be small (7-10 μm in diameter) or large (10-14 μm in diameter). The nucleus is large and round. They help the immune system of the body. They form about 25-30% of leucocytes.

Thrombocytes :  They are the cell fragments formed by megakaryocytes in the bone marrow. Their number ranges between 1,50,000 and 3,50,000 cubic mm. They release blood clotting substances.