ABSTRACT
The physiological process that produces optimal stability is known as homeostasis, a term introduced by Cannon. Homeostasis operates through negative feedback. The operation of a negative feedback system is often compared with a thermostatically controlled heating system. The chapter describes the analogy is a poor one, although it illustrates the basic principles of negative feedback control, and allows us to recognize the limitations of a simple system. If any one of the components fails, the whole system fails. The solution to this is to build redundancy into the control system. This means having more than one of each type of component, preferably with more than one connection between components. While a simple system like a room thermostat might be adequate for controlling room temperature, it has weaknesses that could be fatal in a homeostatic mechanism. When the thermometer detects that the temperature has risen above the set point, it causes the switch to turn off the heater.
