Damaged tissue releases chemicals that activate platelets and stimulate the formation of blood clots. Which of the following predictions about the activity of platelets best describes a positive feedback mechanism?(A) Activated platelets release chemicals that inhibit blood clot formation. (B) Activated platelets release signaling molecules that inhibit cell division in damaged tissue.(C) Activated platelets constrict the blood vessels, stopping blood flow.(D) Activated platelets release chemicals that activate more platelets.

Activated platelets release chemicals that activate more platelets-describes best the positive feedback mechanism of platelets

Explanation:

A positive feedback mechanism is a type of self-amplifying process triggered by a stimulus that leads to greater change along the same direction.  

The steps in homeostasis of blood are – platelet adherence, platelet activation, platelet aggregation, coagulation.

When a blood vessel is damaged or injured, various chemicals are released which cause the platelets to adhere to the walls of the blood vessels. This action causes the platelets to release their own chemicals which stimulate the clotting process furthermore. This process is continuous until the injured bleeding blood vessel is corrected by a clot formation and is an example of positive feedback mechanism.

Platelet activation involves releasing of chemicals like cytokines, chemical mediators and coagulation factors; namely, thromboxane A2, ADP, PDGF, VWF, serotonin etc. Chemicals like ADP, VWF etc are released at high levels with increase in platelet plug formation.  

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