6.4.2 control of blood glucose concentrtion

• 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

  
  

  Glycogenesis, glycogenolysis and gluconeogenesis also affect blood glucose concentration controlled by the

  action of hormones insulin, glucagon and adrenaline.
• 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
• Explain the action of insulin in decreasing blood glucose concentration?

  ● insulin 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
• Beta cells in islets of Langerhans in pancreas detect blood glucose concentration is too high → secrete insulin
• Alpha cells in islets of Langerhans in pancreas detect blood glucose concentration is too low → secrete glucagon
• 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
• 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
• what is 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
• what is 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

  ● 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
• Describe how of type II diabetes can be controlled

  ● Not normally treated with insulin injections 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

  Consider both sides:

  ● 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
• Exam insight: common mistakes ❌(1/7) ?

  ❌*Mixing up glycogenesis, glycogenolysis and gluconeogenesis.*

  Explanation: To remember what these words mean.

  Lysis relates to splitting,

  neo to new

  genesis to creation.
• Exam insight: common mistakes ❌(2/7) ?

  ❌“Insulin opens existing channel proteins in

  the cell-surface membranes of target cells.”

  Explanation: Insulin causes more glucose channel proteins to join the

  cell-surface membrane, increasing permeability to glucose.
• Exam insight: common mistakes ❌(3/7) ?

  ❌“Glucagon converts glycogen to glucose, or

  glycerol / amino acids into glucose.”

  Explanation:This suggests glucagon acts as an enzyme during these

  reactions. Glucagon binds to receptors on the surface of cells

  which leads to activation of enzymes involved in this.
• Exam insight: common mistakes ❌(4/7) ?


  ❌“Insulin / glucagon / adrenaline bind to the

  active site of the receptor.”

  Explanation:Only enzymes have active sites.

  These hormones bind to the receptor directly.
• Exam insight: common mistakes ❌(5/7) ?


  ❌“The amount / level of glucose in the blood

  is too high in people with diabetes.”

  Explanation:The term amount is never accepted.

  You should instead use the term concentration.
• Exam insight: common mistakes ❌(6/7) ?


  ❌“Diabetics are incapable of taking any

  glucose into body cells.”

  Explanation:Due to insufficient insulin production or reduced responsiveness

  of receptors to insulin, less glucose is taken into cells.
• Exam insight: common mistakes ❌(7/7) ?

  ❌“Type II diabetics are less responsive to insulin.”

  Explanation:This is too vague. It is the receptors on their cells that lose responsiveness / sensitivity to insulin.