Which of the following is not regulated through a negative feed back mechanism?

Thrombus formation is an example of positive feedback mechanism. Blood clotting is an example of a valuable use of positive feedback. When a blood vessel is ruptured and a clot begins to form, multiple enzymes called clotting factors are activated within the clot itself. Some of these enzymes act on other unactivated enzymes of the immediately adjacent blood, thus causing more blood clotting. This process continues until the hole in the vessel is plugged and bleeding no longer occurs. Ref: Guyton and Hall Medical Physiology, 11th Edition, Page 8-9; Reversibility of Chronic Degenerative Disease and Hypersensitivity, Volume 1 By William J. Rea, Page 128.