Listen to the sound clip Blood clotting. When a tissue is damaged, blood flows from it and coagulates to form a blood clot. This prevents further blood loss and entry of pathogenic micro organisms which is of clear survival value. In general the blood in undamaged vessels does not clot. A highly complex series of reactions takes place in order for coagulation to occur as well as prevent unwanted clotting. When the blood vessel is damaged the connective tissues of the vessel wall is exposed. Therefore platelets in the... from Olivia (English United Kingdom) TTS Computer AI Voice: