6.4.2 Control of blood glucose concentration

• Describe the factors that influence blood glucose concentration

  ● Consumption of carbohydrates → glucose absorbed into blood

  ● Rate of respiration of glucose eg. increases during exercise due to muscle contraction
• Describe the role of the liver in glycogenesis,

  glycogenolysis and gluconeogenesis

  Glycogenesis Converts glucose → glycogen

  Glycogenolysis Converts glycogen → glucose

  Gluconeogenesis Converts amino acids and/or

  glycerol → glucose
• glucose conversions

  A) glycogenesis

  B) glycogenolysis

  C) gluconeogenesis

  
• Explain the action of insulin in decreasing blood glucose concentration

  Beta cells in islets of Langerhans in pancreas detect high blood glucose concentration - secrete insulin:

  • Attaches to specific receptors on cell surface membrane of target cells (liver/muscle)

  1. more glucose channel proteins to join cell surface membrane

  ○ Increasing permeability to glucose

  ○ So more glucose can enter cell by facilitated diffusion

  2. also activates enzymes involved in glycogenesis

  ○ Lowers glucose concentration in cells, creating concentration gradient

  ○ glucose enters cell by facilitated diffusion
• Explain the action of glucagon in increasing blood glucose concentration

  Alpha cells in islets of Langerhans in pancreas detect blood glucose concentration is too low → secrete

  glucagon:

  ● Attaches to specific receptors on cell surface membranes of target cells eg. liver

  1. Activates enzymes involved in hydrolysis of glycogen to glucose (glycogenolysis)

  2. Activates enzymes involved in conversion of glycerol / amino acids to glucose (gluconeogenesis)

  ● This establishes a concentration gradient → glucose enters blood by facilitated diffusion
• Explain the role of adrenaline in increasing blood glucose concentration

  Fear / stress / exercise → adrenal glands secrete adrenaline:

  ● Attaches to specific receptors on cell surface membranes of target cells eg. liver

  ● Activates enzymes involved in hydrolysis of glycogen to glucose (glycogenolysis)

  ● This establishes a concentration gradient → glucose enters blood by facilitated diffusion
• Describe the second messenger model of adrenaline and glucagon action

  Adrenaline / glucagon (‘first messengers’) attach to specific receptors on cell membrane which:

  1. Activates enzyme adenylate cyclase (changes shape)

  2. Which converts many ATP to many cyclic AMP (cAMP)

  3. cAMP acts as the second messenger → activates protein kinase enzymes

  4. Protein kinases activate enzymes to break down glycogen to glucose
• Suggest an advantage of the second messenger model

  ● Amplifies signal from hormone

  ● As each hormone can stimulate production of many molecules of second messenger (cAMP)

  ● Which can in turn activate many enzymes for rapid increase in glucose
• Compare the causes of types I and II diabetes

  Both - higher and uncontrolled blood glucose concentration; higher peaks after meals and remains high

  Type I

  ● Key point = β cells in islets of langerhans

  in pancreas produce insufficient insulin

  ● Normally develops in childhood due to

  an autoimmune response destroying β

  cells of Islets of Langerhans

  Type II

  ● Key point = receptor (faulty) loses responsiveness /

  sensitivity to insulin (but insulin still produced)

  ● So fewer glucose transport proteins → less uptake of

  glucose → less conversion of glucose to glycogen

  ● Risk factor = obesity
• Describe how of type I diabetes can be controlled

  ● Injections of insulin (as pancreas doesn’t produce enough)

  ● Blood glucose concentration monitored with biosensors; dose of insulin matched to glucose intake

  ● Eat regularly and control carbohydrate intake eg. those that are broken down / absorbed slower

  ○ To avoid sudden rise in glucose
• Suggest why insulin can’t be taken as a tablet by mouth

  ● Insulin is a protein

  ● Would be hydrolysed by endopeptidases / exopeptidases
• Describe how of type II diabetes can be controlled

  ● Not normally treated with insulin injections (as pancreas still produces it) but

  may use drugs which target insulin receptors to increase their sensitivity

  ○ To increase glucose uptake by cells / tissues

  ● Reduce sugar intake (carbohydrates) / low glycaemic index → less absorbed

  ● Reduce fat intake → less glycerol converted to glucose

  ● More (regular) exercise → uses glucose / fats by increasing respiration

  ● Lose weight → increased sensitivity of receptors to insulin
• Describe how you can evaluate the positions of health advisers and the food

  industry in relation to the increased incidence of type II diabetes

  ● Health advisers aim - reduce risk of type II diabetes due to health problems caused (eg. kidney failure)

  ○ So need to reduce obesity as it is a risk factor

  ● Food industry aim - maximise profit
• explain how increasing a cells sensitivity to insulin will lower the blood glucose concentration

  • insulin attaches to specific receptors on target cells
  • more uptake of glucose by channel/transport proteins
• give 2 reasons why pancreas transplants are not used for the treatment of type II diabetes

  • pancreas still produces insulin
  • receptors less sensitive/responsive