How dose human body prevent blood clotting inside your vascular system?

Blood clotting: Your blood has several substances (factors) which cause clotting and several factors which inhibit clotting. Normally these are in a sort of balance and your blood does not clot unless it remains stagnant somewhere like people with certain arrhythmias, or you have an injury, or you are immobilized in bed or sometimes during a long period of sitting.