While out rollerblading with your friends, you hit a crack in the asphalt, fall, and cut and scrape your knee. Blood flows out from the injury and you put pressure on it as you make your way home. After resting with your leg elevated, you notice that the bleeding has stopped. Do you think that the clotting of blood after an injury is a positive or a negative feedback response? Explain your reasoning.

 

Answer:

It is a positive feedback response.

Positive feedback is a self-amplifying process where a stimulus or change leads to even greater change in the same direction. For instance, if a blood vessel is damaged, chemicals begin a chain reaction that causes platelets to stick to the vessel wall and the platelets release more chemicals that accelerate the clotting process and this process ends once the vessel wall has been repaired by a clot.

The fact that te the arrival of platelets at a site releases clotting factors that cause more platelets to arrive at the injury site indicates that this is a positive feedback response.

Reference;

Shibeko, A. M., Lobanova, E. S., Panteleev, M. A., & Ataullakhanov, F. I. (2010). Blood flow controls coagulation onset via the positive feedback of factor VII activation by factor Xa. BMC systems biology, 4(1), 5.