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
• What is Glycogenesis?

  Converts glucose → glycogen
• What is Glycogenolysis?

  Converts glycogen → glucose
• What is Gluconeogenesis?

  Converts amino acids and/or glycerol → glucose
• Explain the action of insulin in decreasing blood glucose concentration:

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

  1)This causes more glucose channel proteins to join cell surface membrane

  ○ Increasing permeability to glucose

  ○ So more glucose can enter cell by facilitated diffusion

  2)This also activates enzymes involved in conversion of glucose to glycogen (glycogenesis)

  ○ Lowering glucose concentration in cells, creating a concentration gradient

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

  ● 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:

  ● 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
• What do Beta cells do?

  Beta cells in islets of Langerhans in pancreas detect blood glucose concentration is too high → secrete insulin
• What do Alpha cells do?

  Alpha cells in islets of Langerhans in pancreas detect blood glucose concentration is too low → secrete glucagon
• 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
• Describe type 1 diabetes:

  ● 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
• Describe type 2 diabetes:

  ● 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