Negative Feedback system:
Inside a negative feedback system, "The product of a certain process suppresses the process itself, as the product of that process inhibits and have certain effects on the same process or mechanism."
Positive Feedback system:
Now, in the positive feedback system,"The product formed from a certain process or mechanism will enhance the frequency of its productivity and will certainly effect the number of products formed due to that very process."
Feedback system and Homeostasis:
Lets suppose if the optimum temperature of the human body is 37.8°centigrade and it some how it drops down to 25°, then eventually the body will enhance thermogenesis and the body temperature will be raised. But, if the product gave rise to more then the optimum temperature which is 37.8° then it will stop the body from doing any more thermogenesis(eventually the product of the process inhibits the process or mechanism). All of this is called as the negative feed back mechanism carried out by the body for homeostasis.Now, when we urinate and the urine pushes to go through the aperture into the the outside environment. While, the urine is required to be removed from the human body in order to keep a balance of liquids inside the human body, which is obviously a part of homeostasis. So, when the urine comes all the way down through the ureter, there are certain chemical changes inside the membranes, as these changes cause the dilation of the aperture while the urine also pushes through the pathway into the outside environment. So, its all due to positive feedback mechanism inside the body.
Explanation:
Negative Feedback Mechanism:During the process of digestion there are certain enzymes which are produced for increasing the rate of digestion inside the human stomach. While its secretion should be kept to an optimum level, and if it exceeds somehow then the optimum level required.It will then cause acidity inside the stomach. When the food goes inside the stomach the required amount of enzymes are secreted by the epithelial cells of the stomach and then it helps in breaking down of the polymers into much simple molecules for getting the required amount of energy for cellular functions. As if the amount or number of enzymes secreted by the body exceeds from a certain level then it will eventually results in causing the acidity inside the stomach. So, for that reason secretion of these enzymes will be inhibited by its over secretion, this is process is called as the negative feedback system inside a human body for keeping the level of homeostasis.The other one can of excessive sweating from the human body, as if its uncontrolled will lead to the situation of dehydration(excessive loss of water and minerals). Now, the body requires the temperature to be set at a certain optimum level and if it exceeds that it will initiates loss of water from the body through the sweat glands and in form of urine. There will be some loss of minerals and water up to a certain level, and if exceeds that level then the process will be inhibited by the product of that process which is obviously excessive loss of water from the body leading to dehydration. Now , the pores present on the skin will be closed and no more urination will be processed in order to keep a balance of all the materials inside the human body.Example of positive feedback mechanism:Vomiting or through up food by the human body is processed by the pathway of positive feedback mechanism. As the material present inside due to anti-peristalsis(which means due imbalance of liquids and enzymes the gut pours the materials outside in the opposite direction). The gastrointestinal tract and the bucal cavity dilates due to the initiation of the anti-peristalses which is obviously following pathway of  the positive feedback mechanism.
