There are negative and positive feedback systems in an organism in order to maintain homeostasis. As for negative feedback system, it consists of a loop of control center, input, output, the effectors and response. It negates the original stimulus. Let's consider the blood pressure. The blood pressure is the force exerted against the walls of blood vessels. If the heart beats faster and harder, the blood pressure increases. In this case, baroreceptors ( receptors in vessel walls) send nerve impulses (input) to the brain ( control center). The brain sends nerve impulses( output) to the heart and blood vessels ( the effectors). The blood vessels dilate (widen) and the blood pressure decreases (response) The blood pressure returns to normal and homeostasis is restored. The original stimulus (blood pressure increase) is negated, and therefore it is called negative feedback system.

The positive feedback system functions differently. It reinforces the change in a controlled condition in the organism. As an example, can serve severe blood loss. Under normal conditions, the heart pumps the blood under sufficient blood pressure. However, severe blood loss decreases the blood pressure and makes the blood cells ( including the heart cells) weaken, therefore they don't function properly and can't pump blood as they usually do. In this case, the reinforcement under positive feedback can lead to life-threatening conditions if there is no medical intervention.