Homeostasis

Your body holds dozens of variables inside narrow ranges: core temperature, blood pressure, blood glucose, the pH and salt content of your blood. Each one is held the same way. A sensory receptor detects the variable, a control center compares it with a set point, and effectors push it back. Because the correction opposes the change, this is negative feedback, and it is how almost all regulation works.

Watch for it everywhere. When you stand up quickly and blood pools in your legs, pressure sensors in your arteries fire less, your brainstem raises heart rate and tightens arterioles, and your blood pressure recovers within seconds. The same loop, with different parts, runs your thermostat, your breathing and your kidneys. Positive feedback, which amplifies a change, is rare and always has an end point, such as childbirth or a clot sealing a wound.