PLATELETS
Platelets look microscopically as round or oval plates with biconvex surfaces they are named as thrombocytes since they aid in the process of thrombus (clot) formation in the blood they are of quarter size of the RBC(i.e2-4u in diameter ) they are anuclear with distinct granules in their cytoplasm there are 250000 to 500000 platelets per cmm of blood they undergo diurnal variations
Origin:
The megakaryocytes known as giant cells of bone marrow eject out pseudopodia which break off as platelets and float freely in the circulating blood they have shorter life span of 5-9 days older and dead platelets are removed by RES cells of spleen and liver
Functions:
1.They initiate clotting by breaking and converting the blood prothrombin into thrombin which is one of the basic substances to form the clot
2.They repair the capillary leak by adhering and patching up the ruptured capillaries
3. They aid syneresis i.e clot retraction
4. They contain some antigenic substances resembling A and B antigens
5. On breaking they liberate serotonin i.e 5 HT (5-Hydroxy-tryptamine )and histamine 5-HT constricts capillaries to give haemostatic effect Histamine causes capillary vasodilatation
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