A morphogenetic determinant specifies cells in a qualitative (“present or absent”) way.

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#Unit 7. System Physiology – Animal

Fibrin formation involves a cascade of enzymatic reactions and a series of numbered clotting factors.

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#Unit 7. System Physiology – Animal

The fundamental reaction is conversion of the soluble plasma protein fibrinogen to insoluble fibrin.

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#Unit 7. System Physiology – Animal

The fibrin is initially a loose mesh of interlacing strands. It is converted by the formation of covalent cross linkages to a dense, tight aggregate (stabilization). 

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#Unit 7. System Physiology – Animal

The initial reaction in the intrinsic system is conversion of inactive factor XII to active factor XII (XIIa).

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#Unit 7. System Physiology – Animal

kininogen and kallikrein, can be brought about 

In vitro by exposing the blood to glass

In vivo by collagen fibers underlying the endothelium

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#Unit 7. System Physiology – Animal

Active factor XII then activates  factor XI, & active factor XI activates factor IX.