Blood: The Vehicle of the Life Force

The blood is a vital fluid composed of cellular components and liquid substance called plasma. The cellular components or blood corpuscles float in the plasma. About 40 to 45% of the volume is made up of blood cells and about 55-60% volume is fluid. The volume of cellular components is determined by hematocrit technique. The total volume of blood is about ¹/₁₂th to ¹/₁₃th of our body weight. The vital energy of the body is generated by metabolic processes through oxidation and enzymatic actions. The blood carries oxygen from the lungs and distributes the same to all organs and tissues. Infact, blood is a vehicle of life force.

Composition of Plasma of Blood: The blood plasma contains the following substances:

• Water: 91 - 92%
• Protein: 7 - 8% (Albumin, globulin and coagulation factors)
• Salts: 0.9% (Sodium chloride, potassium chloride, sodium bicarbonate, salts of calcium, magnesium, phosphorus, iron and trace metals).

In addition to above there are small amounts of organic materials like glucose, cholesterol, urea, uric acid, creatinine and amino acids along with hormones, enzymes and antigens.

Cellular Components: There are three types of cells present on blood:

• Red blood cells (RBCs) or erythrocytes.
• White blood cells (WBCs) or leucocytes.
• Platelets or thrombocytes.

Erythrocytes are circular, bi-concave disc like cells and originate in bone marrow. They are pale buff colored when seen singly, but in masses appear red and give the red color to blood , hence called red blood cells. They contain the vital substance hemoglobin. The amount of hemoglobin present in normal blood is about 15 g/dl. The normal count of RBCs in blood is about 5,000,000 (5 x 10⁶) per microlitre of blood. The average life of red blood cell is about 115 days. Hemoglobin is a complex protein rich in iron. It has an affinity for oxygen and combines with it to form oxy-hemoglobin in RBCs. By means of this function oxygen is carried to the tissues from the lungs. A balanced diet rich in iron and proteins is necessary for the replacement of worn out RBCs. Women require more iron as some is lost in the menstrual flow; in pregnancy the requirements are greater to supply iron for the developing fetus.

Blood Groups: Erythrocytes or RBCs carry at their surface the blood group antigens and there are antibodies in the plasma against the antigen absent at the surface of erythrocytes. There are two antigens: A-antigen and B-antigen. Depending upon the presence and absence of these antigens at the surface of RBCs, there are 4 blood groups:

• Blood group A: Antigen A present at the surface of erythrocytes.
• Blood group B: Antigen B present at the surface of erythrocytes.
• Blood group AB: Antigen A and B present at the surface of erythrocytes.
• Blood group O: No antigen present at the surface of erythrocytes.

In addition to above blood groups, there are a number of sub-groups. Sub-groups and Rhesus factor (Rh factor) in blood is important to be determined by agglutination procedures during compatibility testing. Rhesus factor of fetus is also important in Rh-factor negative mothers.

The white blood cells (WBCs) or leucocytes are transparent and not colored cells. The normal count of WBCs is 4000 to 11000 per microlitre of blood. There are five groups of WBCs:

• Granulocytes or polymorphonuclear cells or neutrophils form about 70 - 75% of total leucocytes' count in blood and provide first line of defence against infectious organisms by phagocytic function.
• Lymphocytes form about 20 - 25% of total leucocytes' count in blood. These cells are called immuno-competent cells and provide active immunity and defence against infectious organisms and tumors. There are further types sub-types of these cells like T-lymphocytes and B-lymphocytes; T-helper and T-suppressor lymphocytes etc.
• Monocytes also provide defence against infectious organisms through phagocytic function. They constitute about 5% of total leucocytes' count in blood.
• Eosinophils are the leucocytes which have active affinity for acidic staining material called eosin and appear red in a blood film after staining. These cells are associated with defence against allergic disorders. Normally they count about 2 - 3% of total leucocytes' count in blood.
• Basophils are the cells which stain with basic dyes and look blue in a stained blood film with blue granules in their cytoplasm. These cells count less than 1% of total leucocytes' count in blood and are associated with allergic disorders.

Platelets or thrombocytes are very small cells, about one third of the size of an erythrocyte. Their normal count is 150,000 to 300,000 per microlitre of blood. They play a vital role in the control of bleeding from an injury and in the clotting of blood.

The blood act as a vehicle or transport system of our body carrying all the cellular components, chemical substance, oxygen and nutrients for the nourishment and defence of body in order to maintain its normal function and preservation of life. Red blood cells convey oxygen to the tissues and remove carbon dioxide. Plasma distributes proteins needed for tissue formation and repair. Blood also carries waste products of metabolism for elimination through excretion by kidneys. Internal secretions, hormones and enzymes are also conveyed by blood from organ to organ or target site by the blood. In nutshell the blood is a vehicle of the life force.