Question

Blood protiens are incapable of blood clotting inside the blood vessels but form blood clot at the injury. How is it possible?

Answer 1

There are a number of reasons:-
1. Heparin is secreted by the endothelial cells that prevents blood from clotting inside vessels.

2. The surface of the cells lining the inside of the blood vessels is smooth. Blood starts clotting when it hits a rough surface. So this prevents that.

3. A layer of glycocalyx on endothelium repels clotting factors and platelets thereby preventing clotting.

4. There is a protein called thrombomodulin which binds with another factor called thrombin that acts as an anticoagulant by inactivating clotting factors V and VIII.