In blood clotting disorders, clotting time is increased, but when there is plalete disorder clotting time is not affected. What is the reason for that. Aren't platelets required for blood clotting. Also when a fibrous mesh is formed, do red blood cells and platelets get stuck in it. Is it why blood clots. Thanks

Platelets are essential in blood clotting. They clump together in order to initiate the blood clotting steps, by reacting with fibrinogen. Vitamin K is also needed. The resulting fibrin/platelet mesh traps red blood cells and forms the clot. Agents that inhibit platelets from forming a clot (such as aspirin) are used to prevent abnormal clotting within a blood vessel that can lead to a stroke or heart attack. However, the coagulation cascade is much more complicated and finely tuned. For a rather good summary see wikipedia (coagulation)