Blood coagulation factor - Circulation
The catalytic sequence of events behaves like an enzyme cascade with each product of a reaction being responsible for the activation of the next reaction. At least 13 different plasma factors have been recognised. A deficiency of even one factor can delay or prevent clotting. Why has such a complex mechanism evolved? Maybe it is essential to have a number of initial clotting responses to a variety of internal and external stimuli that can cause haemorrhage. At the same time, any ambiguous stimuli would not be able to cause intravascular clotting when no injury occurs. Coagulation of blood is inhibited by heparin, a mucopolysaccharide that can be isolated from mammalian liver. A haemostatic mechanism is necessary for most animals. In open circulation the contraction of blood vessel to prevent blood loss does not help, but then open systems have low blood pressure and thus decrease the ' chances of large blood losses.
Table: Blood coagulation factor
Clotting mechanisms are also seen in invertebrates. The simplest mechanism is the agglutination of blood corpuscles without the involvement of plasma proteins. A cellular meshwork forms which helps to close the wound. Contraction of muscles also helps in this process.