Describe Blood Platelets

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Blood Platelets:-

platelets are formed in the blood of mammals only. Their number is 2-4 lac per mm³ . Platelets are oval or circular plasma elements measuring 2-5μ in diameter . They are formed by the fragmentation of megakaryocytes of bone marrow. Platelets do not have nucleus. This feature differentiates them form thrombocytes of lower vertebrates. Platelets have a life span of 2-5 days. In peripheral blood, their number increase during day time but reduces during night. Many platelets factors and enzyme thromboplastin are released by damaged or injured platelets which help in blood clotting. A part from this platelets also secrete a substance serotonin which inhibits the haemorrhagic effects by vasocontriction of blood vessels.

Describe Blood Platelets

Blood Coagulation:-

The coagulation of liquid blood into jelly like clot is called blood coagulation. Oozing of blood starts when a blood vessel gets damaged. Blood coagulation starts within 3-4 minutes and completes within 5-6 minutes resulting in the formation of clot or thrombus. A pale coloured fluid called serum accumulates at the site of blood clotting.

Mechanism of blood coagulation:

A change in the physico chemical state of soluble plasma protein fibrinogen is res- ponsible for the clotting of blood. Fibrinogen is converted into insoluble fibrin the fibres of which trap blood cells to form clot. This process is called blood clotting. The clot starts contracting within few minutes of its formation releasing serum.

Blood coagulation is a complex chemical reaction. According to the International commission on blood coagulation 1954, established to study coagulation of blood following 13 coagulation factors take part in the process of blood coagulation.

  1. Fibrinogen

  2. prothrombin

  3. Thromboplastin

  4. calcium ions (Ca++)

  5. Labile factor, Proaccelerin

  6. Hypothetical factor, Accelerin

  7. stable facto, Proconvertin

  8. Antihaemophilic factor, AHF

  9. Christmas factor or plasma thromboplastin components, PTC

  10. stuart power factor

  11. Plasma Thromboplastin antecedent, PTA

  12. Hageman factor

  13. Fibrin stabilizing factor or laki lovand factor.

out of these factor 1,2,5,7,8,9 and 10 are synthesized in the liver. Blood coagulation completes in three step which are sytstematically depicted.