Controlling Blood Glucose Concentration (Cambridge O Level Biology)

The importance of blood glucose regulation

• Blood glucose concentration must be kept within a narrow range, so it’s another example of homeostasis
• Eating foods containing carbohydrate leads to an increase in blood glucose; in this situation blood glucose levels must be brought back down to normal levels
  • Excess glucose in the blood can lower blood water potential, causing water to move out of body cells into the blood by osmosis
• Periods of fasting, or intense exercise, can lead to a decrease in blood glucose; here the blood glucose levels must be increased back to normal levels
  • Glucose is an essential reactant in respiration, so must be available to body cells at all times

Hormones and blood glucose regulation

• Blood glucose concentration is monitored and controlled by the pancreas
  • The pancreas is an endocrine gland that makes and secretes hormones
  • The pancreas has a separate role in the production of digestive enzymes
• Blood glucose levels are controlled by a negative feedback mechanism involving the production of two hormones; insulin and glucagon
  • A negative feedback mechanism works to reverse any changes, bringing levels back to within normal limits, e.g.
    • Reversing any changes in body temperature to bring core temperature back to normal
    • Reversing changes in blood glucose to maintain normal blood glucose concentrations
• Any changes in blood glucose are detected by the pancreas, which then secretes either the hormones insulin or glucagon in response to any changes:
  • Insulin is produced when blood glucose rises
    • Insulin stimulates liver cells and muscle cells to convert excess glucose into glycogen
    • Glycogen can be stored inside cells
  • Glucagon is produced when blood glucose falls
    • Glucagon stimulates liver cells and muscle cells to convert stored glycogen into glucose
    • Glucose can be released into the blood

Blood glucose regulation diagram

Blood glucose levels are regulated by the pancreas by the actions of the hormones insulin and glucagon. Adrenaline may also be involved when blood glucose levels drop too far

• Type 1 diabetes is a condition in which blood glucose levels cannot be regulated; this is because the insulin-secreting cells in the pancreas are not able to produce insulin
  • This is the result of an autoimmune condition in which the body's immune system attacks and destroys cells in the pancreas
• Signs of type 1 diabetes include
  • High blood glucose levels
  • Glucose in the urine
• Treating type 1 diabetes involves injecting insulin
  • Insulin causes the liver to convert glucose into glycogen, which reduces blood glucose levels
• People with type 1 diabetes need to monitor their blood glucose levels throughout the day as their levels of physical activity and their diet affect the volume of insulin that should be injected
• A carefully regulated diet, and regulated exercise, can also help to control blood glucose levels