Negative Feedback Mechanisms (WJEC GCSE Biology)

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