Feedback systems

A cycle of events where the body is monitored, evaluated, changed, remonitored etc. Each variable is called a controlled condition and any condition that changes it is called a stimulus.

A feedback system contains 3 elements a Receptor, Control centre and Effector.

Receptor: monitors changes and sends input signals (chemicals and impulses) to the control centre along Afferent pathways
Control Centre: eg the brain etc sets a range of values that is acceptable evaluates input and sends output commands (chemicals impulses and hormones) along Efferent pathways
Effector: the reciever of output from the control centre which produces a response almost all organs and tissues act as effectors.

In feedback systems the responses recieved either negate the controlled condition or enhance the controlled condition.

A negative feedback loop reverses or weakens a change in a controlled condition and slows or stops it brings it back to balance. in a positive feedback loop a controlled condition is propelled or strengthened and can run away to reach balance.
In a positive feedback loop the control centre sends commands to the effector and the effector produces a response that adds to the initial change ie more of that. an example is childbirth where contractions and hormone release cause the cervix to open.
Some positive feedback loops can lead to death such as blood loss where the loss of blood results in blood pressure decreasing and the heart not being able to pump as effectively. Hypoglycemia would be another where a drop in blood sugar impairs your ability to eat or get sugar to elevate blood glucose.

The science that deals with when where and why disease occurs and how they are transmitted in a community is epidemiology.