Wednesday, September 30, 2015


Blood may be described as a specialized connective tissue in which there is liquid inter cellular substance called plasma and formed elements, the red blood cells, white blood cells and plalelets suspended in the plasma.

Functions of blood

1 Transport of respiratory gases: It carries oxygen from the ungs to the tissue and carbon dioxide from tissue to the lungs.

2. Transport of nutrition :  It carries digested food material absorbed from the intestine to the tissue cells for utilization. It also carries nutritive materials from one place of the body to the other.

3. It acts as a vehicle:Through the hormones, the vitamins, & other essential chemical are brought to their places of activity.

4. Drainage of waste products:It carries the waste product of cellular activity & brings them to the organ of excretion like kidney & lungs.

5. Maintenance of the water balance.
6. Maintenance of acid base balance.
7. Maintenance of ion balance between the cells and surrounding fluid.
8. Regulation of body temperature.

9. Defensive action: Blood acts as a great defensive mechanism in two ways - (a) the white cells due to their phagocytic properties engulf the bacteria and foreign particles. (b) It develops antibodies which combat toxin agent.

10. By the property of coagulation it guards against haemorrhage.
11. Regulation of blood pressure.

                  Composition of blood

Blood is a highly complex fluid which composed of two parts – a liquid, called plasma & different types of cells which remain suspended in the plasma. The cells are called the blood corpuscles. The plasma constitutes about 55% and the cells about 45% of the total volume of the human blood.
The general composition of whole blood is as follow-

(A)          Cells-

1.     Red blood corpuscles (RBC) or erythrocytes
2.     White blood corpuscles (WBC) or leucocytes
3.     Platelets or thrombocytes.

(B)          Plasma-

1.     Water- 91 to 92%
2.     Solids- 8 to 9%
(a)  Inorganic constituents- 0.9% like sodium, potassium, calcium, magnesium, phosphorus, iron, copper etc.
(b) Organic- 7.5% Urea, uric acid, ammonia, proteins & amino acids, fats, carbohydrates, internal secretions & coloring matter like bilirubin.

Formed elements of the blood

There are three types of cellular elements in the blood-
1.     Red blood corpuscles (RBC)
2.     White blood corpuscles(WBC)
3.     Platelets

1.     Red blood corpuscles (Erythrocytes):The matured human erythrocyte is a circular, biconcave, non nucleated disc. The edges are rounded and thicker than the centre. The mature red cell is soft, flexible and can readily squeeze through narrow capillaries.

The diameter of the red cell when in the body varies from 5.5 µ to 8.8 µ. When seen on the slide the average size of the red cell is about 7.2 µ. The average thickness of the red cell is about 2.2 µ.


1.     Red cells carry oxygen & carbon dioxide.
2.     Acid base balance.
3.     RBC help to maintain the viscosity of the blood.
4.     Red cells maintain the ion balance.
5.     Various pigments are derived from the haemoglobin e.g. bilirubin & biliverdin.


Haemoglobin is the red pigment of blood. It consist of two parts- one part (96%) is a specific simple protein known as globin and the other (4%) is a non specific prothetic group – an iron containing pigment called haem.
The normal range of haemoglobin is 13.5 to 17.5 grams per deciliter in men and 12.0 to 15.5 gram per deciliter in women.

2.White blood corpuscles: The white blood corpuscles are an important variety of the blood. These cells differ from the red cells in many respects

1.     They do not contain haemoglobin.
2.     They are bigger in size.
3.     They are nucleated living cells.
4.     They are much less in number.
5.     Their span of life is shorter.
6.     Their functions are absolutely different from those of red cells.
7.     There are several varieties of leucocytes, whereas red cells are only of one variety.
Total number: The average total number of white cells is 6000 to 8000 per cubic mm, the normal range being 4000 to 11000 per cubic mm. The average ratio of the total white cell count with total red cell count is about  1:700 (i.e. for one WBC there are 700 RBC.

classification: The classification is as follow-

1. Granulocytes or granular leucocytes: Cells with granular cytoplasm. they are formed in the bone marrow from the time of birth onwards.These cells are of the following types-

a. Neutrophil: Neutrophil is about 10-12µ in diameter. Most numerous in the adult blood about 60-70% of total leucocytes. The nucleus is many lobed. The number lobes varies from 2 to 7 or more. Absolute number is 3000 to 6000 per cubic mm.

b. Eosinophil: Eosinophil is about 10 to 12µ in diameter. The nucleus is commonly two - lobed. Absolute number is 150 to 400 per cubic mm.

  c. Basophil: Their size is somewhat smaller with diameter of about 8 to  10µ. The nucleus is usually kidney shaped. Normal count is 0 to 100 per cubic mm.
Increase of granulocytes in the blood is called as granulocytosis.
Diminution of granulocytes in the blood is called as granulocytopenia. Complete disappearance of granulocytes in the blood is called as agranulocytosis.

2. Lymphocytes:

1. Small lymphocyte: It is slightly larger than the red cell. The diameter is about 7.5µ. The nucleus is relatively large and occupies the major part of the cell.

2. Large lymphocyte: It is about 12µ in diameter. The nucleus may be round or kidney shaped. Large lymphocytes are very few in number in adults (4-8%) but are very frequent in children. Normal count of lymphocytes is 1500 to 2700 per cubic mm.

3. Monocytes: These also known as large mononuclear cell and transitional cell. The diameter is about 16 to 18µ. The nucleus is round or oval when the cells are young. But as they grow older, the nucleus becomes becomes kidney shaped or horse shoe shaped.    

                   Functions of white blood corpuscles

1. Phagocytosis: when a bacteria invade the body, the leucocytes pass out the blood vessels and surround the threatened area and engulf the bacteria and destroy them. This process is known as phagocytosis.
2. Antibody formation: Lymphocytes manufacture β and \gamma fraction of serum globulin. Immune bodies are associated with \gamma globulim fraction. So lymphocytes play an important role in the defensive mechanism of the body.
3. Formation of fibroblasts: It is believed that the lymphocytes may be converted into fibroblasts in an area of inflammation and thus help in the process of repair.

No comments:

Post a Comment