Question

1. 1. Name the formed elements which are useful in blood coagulation. 
   2. Give its normal number per cubic millimetre (mm³) in human blood.
2. Comment on the shape and secretion of the above mentioned formed elements.
3. Explain in brief the mechanism of blood coagulation.

Answer 1

(a)

1. Thrombocytes are cellular fragments formed from the large cells called megakaryocytes. These are produced in bone marrow. Thrombocytes are useful in blood coagulation.
2. Normal count of thrombocytes in human blood is about 2.5 – 4.5 lakh/mm³ of blood. 

(b) Shape and secretion of thrombocytes:

1. Thrombocytes are very small, oval shaped cell fragments without nucleus.
2. Platelets secrete platelet factors which are essential in blood clotting. They also seal the ruptured blood vessels by formation of platelet plug/ thrombus. They secrete serotonin a local vasoconstrictor.

(c) Mechanism of blood coagulation: Clotting or coagulation is the process of converting the liquid blood into a solid form.

1. Intrinsic and extrinsic processes involve interaction of various substances called clotting factors by a step wise or cascade mechanism. There are in all twelve clotting factors numbered as I to XIII (factor VI is not in active use).
2. Interaction of these factors in a cascade manner leads to formation of the enzyme thrombin. Thromboplastin, helps in the formation of enzyme prothrombinase.
3. This enzyme inactivates heparin and it also converts inactive prothrombin into its active thrombin.
4. Thrombin converts soluble blood protein fibrinogen into insoluble fibrin. Fibrin forms a mesh in which platelets and other blood cells are trapped to form the clot.