Negative Feedback Mechanisms
Higher Tier Only
- Negative feedback occurs when conditions change from the ideal or set point and returns conditions to this set point
- It works in the following way:
- if the level of something rises, control systems are switched on to reduce it again
- if the level of something falls, control systems are switched on to raise it again
- Negative feedback mechanisms are usually a continuous cycle of bringing levels down and then bringing them back up so that overall, they stay within a narrow range of what is considered ‘normal’
- Changes from the optimal internal conditions result in both the body's hormonal and nervous systems compensating for the change and restoring the optimal conditions
- Examples of body conditions that are controlled by negative feedback are core body temperature and blood glucose concentration
Negative feedback diagram
The negative feedback cycle
Control of blood glucose by negative feedback
- The control of blood glucose concentration is an example of homeostasis by negative feedback
- The pancreas and liver work together to control blood glucose levels
- To carry out this role, the pancreas makes and secretes the hormones insulin and glucagon into the bloodstream
- If the blood glucose concentration gets too high:
- Cells in the pancreas detect the increased blood glucose levels
- The pancreas produces the hormone insulin, secreting it into the blood
- Insulin stimulates muscles and the liver to take up glucose from the bloodstream and store it as glycogen (a polymer of glucose)
- This reduces the concentration of glucose in the blood back to normal levels, at which point the pancreas stops secreting insulin
- If the blood glucose concentration gets too low:
- Cells in the pancreas detect the decreased blood glucose levels
- The pancreas produces the hormone glucagon
- Glucagon causes the glycogen stored in the liver to be converted into glucose and released into the blood
- This increases the concentration of glucose in the blood back to normal levels, at which point the pancreas stops secreting glucagon
Control of blood glucose by negative feedback diagram
The regulation of blood glucose levels by negative feedback
Examiner Tip
A handy way to remember which hormone is released during the control of blood glucose is this tip:
- INsulin takes glucose IN to the liver
- GlucaGON is needed when glucose is GONe