Negative Feedback Mechanisms (WJEC GCSE Biology: Combined Science)

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

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