Posted on Apr 1, 2010 in Health/Medical Sciences | 1 comment
why does blood clot in a wound but not while flowing through blood vessels
The blood contains as many as one million platelets per drop of blood. Platelets are not whole cells, but rather small packets of membrane-bounded cytoplasm. Damage to the endothelial lining of a blood vessel exposes materials (ADP and thromboxane A2) that cause platelets to stick to the endothelial cells and then other circulating platlets are caused to adhere to the platelets outling the areas of the wound. These platelets release factors (fibrinogen, thrombospondin, fibronectin, factor V, etc.) that promote accumulation of fibrin, a circulating protein, and induce vasoconstriction (construction of cut blood vessels). A blood clot is a meshwork of fibrinogen, platelets, blood cells woven together by fibrin. Blood can, of course, also clot abnormally within the vessels leading to possible strokes, heart attacks, etc.
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