Physiological processes are commonly moderated via two distinct feedback mechanisms –positive and negative feedback
- Homeostatic processes are controlled by negative feedback and hence these systems occur more commonly within the body
Negative Feedback
Negative feedback involves a response that is the reverse of the change detected (it functions to reduce the change)
- A change is detected by a receptor and an effector is activated to induce an opposite effect – this promotes equilibrium
Examples of processes that utilise negative feedback loops include homeostatic systems, such as:
- Thermoregulation (if body temperature changes, mechanisms are induced to restore normal levels)
- Blood sugar regulation (insulin lowers blood glucose when levels are high ; glucagon raises blood glucose when levels are low)
- Osmoregulation (ADH is secreted to retain water when dehydrated and its release is inhibited when the body is hydrated)
Example of a Negative Feedback Loop – Thermoregulation
Positive Feedback
Positive feedback involves a response that reinforces the change detected (it functions to amplify the change)
- A change is detected by a receptor and an effector is activated to induce the same effect – this promotes further change
- Positive feedback loops will continue to amplify the initial change until the stimulus is removed
Examples of processes that utilise positive feedback loops include:
- Childbirth – stretching of uterine walls cause contractions that further stretch the walls (this continues until birthing occurs)
- Lactation – the child feeding stimulates milk production which causes further feeding (continues until baby stops feeding)
- Ovulation – the dominant follicle releases oestrogen which stimulates LH and FSH release to promote further follicular growth
- Blood clotting – platelets release clotting factors which cause more platelets to aggregate at the site of injury
Example of a Positive Feedback Loop – Child Birth
