Friday, 30/09/2016

Blood is called the connective tissue. The colour of blood is red due to the presence of haemoglobin in red blood cells.
Components of blood
There are four main components of Blood:
1. Plasma
2. Red Blood Corpuscles or Red Blood cells
3. White Blood Corpuscles or White Blood cells
4. Platelets.

The colourless liquid part of the blood is called plasma where the red blood cells, white blood cells and platelets are floating.

Red Blood Corpuscles or Red Blood cells
The red blood cells are the carriers of oxygen from the lungs to all cells of the body. Lifetime of each RBC is near about four months. But RBCs are made very fast in our bone marrow. Most of the cells in blood are RBCs. Deficiency of Iron causes Anaemia.

White Blood Corpuscles or White Blood cells
White blood cells fight against infection and protects human body from diseases. They made antibodies which provides immunity and thus WBCs are soldiers of human body. WBCs are much less in number as compared to WBCs.


Platelets are tiny fragments also formed in bone marrow. The normal platelet count of healthy person is 1,50,000- 3,50,000 per microliter of blood. Platelets help in blood clotting and that is why bleeding stops after sometime due to any cut or wound.

Structure and production of Platelet
Platelets are not actually true cell but very tiny fragments of cells floating in the plasma. Platelets are also produced in the bone marrow. The large bone marrow cells Megakaryocytic undergo fragmentation which releases more than 1000 platelets per Megakaryocytic.

Special Function of Platelets
Platelets are the lightest and easily comes along the surface of vessel wall lined by endothelium, endothelium prevents anything from sticking to it. When there is an injury, endothelium layer is broken and platelets are first exposed to react with the injury. The basic function of platelets is to stick with any foreign surface and then to stick together. Platelets helps in blood clotting.
Blood Clotting
During any injury, blood vessels break and blood starts flowing out of the wound, the excessive blood loss can be dangerous and can even cause death. So, bleeding should be stopped that is why our body has its own mechanism of preventing loss of blood by forming a blood clot.
The mechanism of blood clot is a process in which series of chemical reactions take place. The main steps in clotting or coagulation of blood are given below:
1. As blood flows out from injury or cut, the platelets reacts with injury and release a substance called Thromboplastin.
2. Thromboplastin in the presence of calcium converts prothrombin present in blood plasma into another protein called thrombin.
3. Thrombin acts on the soluble protein fibrinogen present in blood plasma and converts it into insoluble protein fibrin.
4. The fibres of fibrin form a thick mesh across the wound and red blood cells gets entangled in the mesh of fibrin fibres forming a blood clot.

And thus blood clot blocks the ruptured blood vessel and prevents further bleeding.

Disorders of Platelet Number
The low platelet count disorder is called thrombocytopenias. Thrombocytopenias can be caused by the inefficiency of bone marrow to produce the normal platelet count. It can also be caused due to destruction of platelets after their production and release in the blood.

Drug induced thrombocytopenia
Some drugs reacts with platelets and human body recognize this combination as foreign body and thus body makes an antibody to destroy this drug coated platelets and therefore platelets are destroyed.

Immune thrombocytopenia
It is caused by both the increased destruction and also decreased bone marrow production. The autoantibodies produced WBCs reacts with bone marrow cells and inhibits platelet production.