Regulation of Blood Glucose (SL IB Biology)

Type 1 diabetes

• Type 1 diabetes is a condition in which the pancreas fails to produce sufficient insulin to control blood glucose levels
• It normally begins in childhood due to an autoimmune response whereby the body’s immune system attacks the β cells of the islets of Langerhans in the pancreas
• The damage to the β cells means that insulin production can no longer take place, and blood glucose concentration can therefore not be regulated
• Type 1 diabetes is normally treated with regular blood tests, insulin injections and a modified diet
  • Such a diet may involve a reduction in carbohydrate intake

Type 2 diabetes

• Type 2 diabetes is more common than type 1, and usually develops in older adults
• In type 2 diabetes the pancreas still produces insulin but the cell membrane receptors to which insulin binds have reduced in number or no longer respond
  
  • The inability of cells to respond to insulin can be described as insulin resistance
• The pancreas will attempt to compensate for this by secreting more and more insulin; eventually insulin production will no longer be able to compensate for the reduced cellular response
• There is a reduced glucose uptake which leads to uncontrolled high blood glucose concentration
• Type 2 diabetes is managed by
  • Medication to lower blood glucose
  • A low carbohydrate diet 
    • Any food that is rapidly digested into sugar will cause a sudden, dangerous spike in blood sugar
  • An exercise regime that lowers blood glucose
• Obesity is a major risk factor for type 2 diabetes; the over-production of insulin in response to a high-carbohydrate diet triggers the development of insulin resistance

Type 1 and type 2 diabetes table

• It is essential that blood glucose concentration is kept within narrow limits
  • Glucose is essential for respiration, so it is important that blood glucose levels do not drop too low
  • Glucose is soluble, so blood glucose concentration affects the osmotic balance between the cells and the blood
• The control of blood glucose concentration is a key part of homeostasis
• Blood glucose concentration is controlled by two hormones which are secreted into the blood by specialised tissue in the pancreas
• This tissue is made up of groups of cells known as the islets of Langerhans
  • The islets of Langerhans contain two cell types:
    • α cells that secrete the hormone glucagon
    • β cells that secrete the hormone insulin
  • These α and β cells are involved with monitoring and responding to blood glucose levels

The islets of Langerhans form the endocrine tissue of the pancreas, while the exocrine tissue is involved with the production of digestive enzymes

The effects of insulin

• Blood glucose concentration increases after a meal that contains carbohydrate
• This increase in blood glucose is detected by the β cells in the pancreas, which synthesise and secrete insulin
• Insulin is transported in the blood to target cells all over the body
  • Insulin's main target cells are in the liver and muscles
• The effects of insulin include: 
  • Glucose channels in cell surface membranes open, and glucose moves out of the blood and into the body cells by facilitated diffusion
  • Liver and muscle cells convert excess glucose into glycogen to be stored; this is glycogenesis
  • An increase in the rate of respiration, using up glucose
  • Conversion of glucose to fatty acids, resulting in fat storage
• Insulin lowers blood glucose concentration

 The effects of glucagon

• Glucagon is synthesised and secreted by α cells when blood glucose falls
  • Blood glucose could fall after a period of fasting, or after exercise
• Glucagon is transported in the blood to target cells
• The effects of glucagon include:
• • The activation of enzymes that enable the hydrolysis of glycogen in liver and muscle cells, releasing glucose that enters the blood; this is glycogenolysis
  • A decrease in the rate of respiration
  • Amino acids are converted to glucose; this is gluconeogenesis
• Glucagon increases blood glucose concentration

Regulation of blood glucose diagram

Blood glucose is regulated by insulin and glucagon