The top is homeostatic.
Even though there is a ripple, the variation of the ripple remains around the same average
It is a small variation around a specific value
The bottom is allostatic.
Intially, it varies around 37, then the temperature increases and it varies around 40, not 37.
This is what happens when someone has a fever.
It varies around different values
The component that is at the blunt end affects the component on the arrow end.
In this case, a change in component 1 directly leads to a change in component 2, a change in
component 2 does not change anything in component 1.
It doesn’t go backwards, only one way + sign = a change in the same direction
If component 1 gets smaller, component 2 gets smaller
- sign = a change in the opposite direction
These components are connected in a loop, if there was no connection between 1 & 3, it would
be a feed forward not a feedback system
Comparing unit compares output from sensor with a set point.
If they are equal, nothing happens
If the reading of sensor is lower than the set point, the comparing unit will turn on the
controlled(furnace) that will increase the air temp
If the temperature of sensor is too high, then nothing happens and furnace shuts off
This is an example of a loop with components
In a fever, the set point changes in the hypothalamus and the system will just regulate around the
COMPONENT A ---(+)----> COMPONENT B ----(+)-----> COMPONENT C -----(-)-----> COMPONENT A
If A gets bigger, B gets bigger, then C gets bigger, then A gets smaller
Component c have negative feedback control towards component A
Negative feedback loops tend to stabilize the control variable
There may be some ripple and variation, but the components of a negative fed back system
interact in a way that stabilizes the system Positive feedback drives a system to its extreme values (death)
If a change in component A gets smaller, B would get smaller, C would get smaller, A would get
even smaller, etc.
Positive feedback is uncommon in physiological systems because they drive things to extremes.
They do not work with life.
Perturbation: Anything that causes a change in a system
Perturbation can happen anywhere in the loop