Write a detailed note on Blood

Blood

• Blood is the main circulatory medium in the human body. 
• It is a red-colored fluid connective tissue.

Components of Blood: 

• The blood consists of two main components. 
• The fluid plasma and the formed elements (blood cells) which are found suspended in the plasma.

Plasma: 

• It is slightly alkaline, containing non-cellular substance which constitutes about 55% of the blood. 
• Organic substances like proteins, glucose, urea, enzymes, hormones, vitamins and minerals are present in the plasma.

Formed Elements of Blood: 

• Blood corpuscles are of three types

1. Red blood corpuscles (RBC) Erythrocytes or
2. White blood corpuscles (WBC) Leucocytes
3. Blood platelets or Thrombocytes.

Red blood corpuscles (Erythrocytes)

• They are the most abundant cells in the human body. RBCs are formed in the bone marrow. 
• The RBCs impart red colour to the Erythrocytes blood due to presence of respiratory pigment hemoglobin. 
• Matured mammalian RBCs do not have cell organelles and nucleus. 
• They are biconcave and disc-shaped. 
• Their life span is about 120 days. 
• RBC is involved in the transport of oxygen from lungs to tissues.

White blood corpuscles (Leucocytes)

• WBC’s are colorless. 
• They do not have hemoglobin and are nucleated cells. 
• It is found in the bone marrow, spleen, thymus and lymph nodes. 
• They are capable of amoeboid movement

The white blood corpuscles can be grouped into two categories:

1. Granulocytes 
2. Agranulocytes.

Granulocytes

• They contain granules in their cytoplasm. 
• Their nucleus is irregular or lobed. 
• The granulocytes are of three types

1. Neutrophils 
2. Eosinophils
3. Basophils

Neutrophils

• They are large in size and have a 2-7 lobed nucleus. 
• These corpuscles form 60% -65% of the total leucocytes. 
• Their numbers are increased during infection and inflammation.

Eosinophils

• It has a bilobed nucleus and constitute 2% – 3% of the total leucocytes. 
• Their number increases during conditions of allergy and parasitic infections. 
• It brings about detoxification of toxins.

Basophils

• Basophils have lobed nucleus. 
• They form 0.5-1.0% of the total leucocytes. 
• They release chemicals during the process of inflammation.

Agranulocytes

• Granules are not found in the cytoplasm of these cells. The agranulocytes are of two types: 

1. Lymphocytes 
2. Monocytes

Lymphocytes

• These are about 20-25% of the total leucocytes. 
• They produce antibodies during bacterial and viral infections.

Monocytes

• They are the largest of the leucocytes and are amoeboid in shape. 
• These cells form 5-6 % of the total leucocytes. 
• They are phagocytic and can engulf bacteria.

Blood Platelets or Thrombocytes

• These are small and colorless. 
• They do not have nucleus. 
• There are about 2, 50,000 – 4, 00,000 platelets / cubic mm platelets of blood. 
• Life span of 8-10 days. 
• They play an important role in clotting of blood. 
• Platelets form clot at the site of injury and prevent blood loss.