prothrombin - thrombin =the last common pathway. prothrombin is made into thrombin by Va &Xa (activator 10 and 5) thrombin is then used to catalyse the reaction of fibrinogen to fibrin. fibrin is then utilised to create a cross-linked fibrin clot, which is used by platelets to clot cuts and wounds

extrinsic pathway - if cells are disrupted near endothelial cells, including themselves they can release cells known as tissue factor (a by-product of trauma). the release of tissue factor causes the activation of activator 10 (used in the common pathway) activator 10 is activated by activator 7 located in the extrinsic pathway (activator 7 is activated by tissue factor)

intrinsic pathway - exposed collagen under endothelial cells causes a pathway of reactions which then activates factor 10

1 molecule of activator 10 can catalyse the activation of a 1000 molecules of thrombin

the increased amount of thrombin result in the increased activation of platelets. which creates enhanced formation of fibrin (fibrin forms the mesh which stabilises the platelet plug in an arterial clot and holds together the RBC in a venous clot)

what does every coagulation cascade require?

ionised calcium

steps of a coagulation test (prothrombin time measurements) extrinsic - continued pathway mechanism measure

all coagulation tests are done on citrated plasma this is because Citrate acts as a calcium chelating agent (it removes all calcium from the samples) to prevent coagulation of the sample so that all the clotting factors are preserved and can be evaluated

at 37 degrees C thromboplastin and Calcium added

time is then measured until a clot forms

(time is usually 11-14s if time is higher it usually indicates low levels of II X VII)

warfarin is a drug that is prescribed to people with heart valves etc it acts to reduce blood clotting in the blood it reduces active II VII IX X so is a useful measure of dose