MRCP revision battle 14.2: The clotting cascade

Before we start tackling clotting disorders a recap of the clotting cascade would be useful.


A schematic of the clotting cascade is:

Its really important to get this in your head as various questions are likely to be indirectly testing your knowledge of it.  I remember the intrinsic pathway into the common pathway as by a little jingle of     " 12,11,9 then 10 (pause) 2, 1 then back again " with the 'back again' bit referring to factor 13 getting in on the action right at the very end to stablise the clot and hence the numbers returning back to being higher.

Also note where VIIIa and Va are involved.



Now look at the same schematic again but with the addition of activated protein C and antithrombin:

So as well as learning the cascade itself make sure the following are etched in your brain:

• activated protein C inhitbits VIIIa and Va
• antithrombin inhibits Xa and IIa 
• protein C is converted to activated protein C by protein S        and finally
• factors II, VII, IX, X are vitamin-K dependent (method of remembering: '1972')

With all that groundwork covered, lets  move on to battle 14.3 and put a bit of it into practice.