Thrombin is produced in the liver

Thrombin is formed from Prothrombin. Thrombin is produced by the enzymatic cleavage of two sites on prothrombin by activated X factor.

Thrombin is a protein

Cellular Response • Thrombin is an enzyme • Catalyzes the final step in

the clotting process:o the conversion of

fibrinogen to fibrin • Fibrin forms threads that are

woven into a clot, stopping bleeding.

• Thrombin also activates a factor that catalyzes more fibrin productiono Positive feedback

Is the result of the pathway demonstrating positive or negative feedback?

ThrombinThrombin is a factor that facilitates the clotting of blood by catalyzing conversion of fibrinogen to fibrin. Positive feedback mechanisms like blood clotting enhance the original stimulus.

Blood clotting is a positive feedback loop because the clot keeps growing until it is fully formed and must form quickly, especially if the blood vessel is large. Once a vessel is damaged, platelets start to cling to the injured site and release chemicals that attract more platelets. The platelets continue to pile up and release chemicals until a clot is formed. The pathway takes blood from a nonclotting state to a clotting state for as long as it’s needed for the clot to form. When the clot has formed, the mechanism for clotting just stops, there is no reverse mechanism that slows and stops clotting. It keeps growing until stopped.

Consequence of AlterationInsufficient bleeding and

prolonged bleedingIn hemophilia there is a

factor 8 deficiency. If this protein is not found in the pathway, thrombin is never able to change fibrinogen to fibrin and blood clots cannot form

Pathway/mechanismPlatelets release clotting factors which

trigger the formation of thrombin.Thrombin activates a factor that catalyzes the

formation of more thrombin, which drives clotting to completion.

Thrombin then activates fibrin which helps form webs to clot.

In other words…

Thrombin uses a second messenger to help clot the blood and stop the bleeding. It never directly comes in contact with the cell to communicate.

Clotting factors: platelets, damaged cells, plasma.

video

http://www.hopkinsmedicine.org/hematology/coagulation.swf