Negative feedback

Negative feedback is the main way the body keeps conditions such as temperature, blood glucose and blood pressure inside a narrow, healthy range, the steady state called homeostasis. The word negative does not mean harmful: it means the response acts in the opposite direction to the original change, pushing a value back toward its set point whether it has drifted up or down.

A feedback loop has three parts. A sensor, or receptor, detects the variable; a control center, often in the brain or an endocrine gland, compares it with the set point; and an effector, such as a muscle or gland, makes the correcting change. When blood glucose climbs after a meal, beta cells in the pancreas release insulin, body cells take up glucose, and as the level falls, insulin secretion slows. Body temperature works the same way, with sweating and wider skin blood vessels when the body is too hot, and shivering when it is too cold.

Hormone systems rely on it too: thyroid hormones in the blood hold back the hypothalamus and pituitary that drive their own release. When a negative feedback loop fails, disease can follow, as in diabetes mellitus.