Feedback Systems

Homeostatic control relies on feedback systems. A feedback system is a control loop in which the result of a response affects the process that caused it.Every feedback system has the same basic parts:- Stimulus: a change in a variable away from the set point.
- Receptor: detects the change, for example thermoreceptors in the skin or hypothalamus.
- Control centre (coordinator): compares the information with the set point and decides on a response, for example the hypothalamus or the islets of Langerhans in the pancreas.
- Effector: a muscle or gland that carries out the response.
- Response: changes the variable.Information passes from receptor to control centre to effector by nerve impulses, by hormones in the blood, or by both.The key feature is feedback: the receptor keeps monitoring the variable after the response, so the control centre receives information about the effect of its own response. This allows the system to adjust continuously.There are two types:Negative feedback: the response reverses the change, returning the variable towards the set point. Most homeostatic systems work this way.Positive feedback: the response increases the change, moving the variable further from its starting value.Many systems have separate mechanisms to correct a rise and a fall (for example insulin and glucagon for blood glucose). This gives a greater degree of control than a single mechanism would.