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Describe the structure and functions of thrombocytes

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Thrombocytes are also known as platelets.

  • Platelets are small irregularly shaped cells formed from large bone marrow cells called megakaryocytes.
  • There are about 250,000 platelets per cubic millimetre of blood.
  • They initiate the process of blood clotting.
  • The process of clotting involves a series of complex reactions whereby fibrinogen is converted into a fibrin clot.
  • When blood vessels are injured platelets are exposed to air and they release thromboplastin (thrombokinase) which initiates the blood clotting process.
  • Thromboplastin neutralises heparin the anti-clotting factor in blood and activates prothrombin to thrombin.
  • The process requires calcium ions and vitamin K.
  • Thrombin activates the conversion of fibrinogen to fibrin which forms a meshwork of fibres on the cut surface to trap red blood cells to form a clot.
  • The clot forms a scab that stops bleeding and protects the damaged tissues from entry of micro-organisms.
  • Blood clotting reduces loss of blood when blood vessels are injured.
  • Excessive loss of blood leads to anaemia and dehydration.
  • Mineral salts lost in blood leads to osmotic imbalance in the body.
  • This can be corrected through blood transfusion and intravenous fluid.
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