[3.6.4.2] Control of Blood Glucose Concentration

Question 1

Describe the factors that influence blood glucose concentration.

Answer 1

• Consumption of carbohydrates -> glucose absorbed into blood.
• Rate of respiration of glucose e.g. increases during exercise due to muscle contraction.

Question 2

Describe the role of the liver in glycogenesis, glycogenolysis and gluconeogenesis.

Answer 2

GLYCOGENESIS

• Converts glucose -> glycogen.

GLYCOGENOLYSIS

• Converts glycogen -> glucose.

GLUCONEOGENESIS

• Converts amino acids and/or glycerol -> glucose.

Question 3

Explain the action of insulin in decreasing blood glucose concentration.

Answer 3

• Beta cells in islets of Langerhans in pancreas detect blood glucose concentration is too high -> secrete insulin:
• Attaches to specific receptors on cell surface membranes of target cells e.g. 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.

Question 4

Explain the action of glucagon in increasing blood glucose concentration.

Answer 4

• 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 e.g. 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.

Question 5

Explain the role of adrenaline in increasing blood glucose concentration.

Answer 5

• Fear / stress/ exercise -> adrenal glands secrete adrenaline.
• Attaches to specific receptors on cell surface membranes of target cells e.g. liver.
• Activates enzymes involved in hydrolysis of glycogen to glucose (glycogenolysis).
• This establishes a concentration gradient -> glucose enters blood by facilitated diffusion.

Question 6

Describe the second messenger model of adrenaline and glucagon action.

Answer 6

• 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.

Question 7

Suggest an advantage of the second messenger model.

Answer 7

• 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.

Question 8

Compare the causes of types I and II diabetes.

Answer 8

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

TYPE I

• Key point = beta cells in islets of Langerhans in pancreas produce insufficient insulin.
• Normally develops in childhood due to autoimmune response destroying beta cells of islets of Langerhans.

TYPE II

• Key point = receptor 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.

Question 9

Describe how type I diabetes can be controlled.

Answer 9

• 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 e.g. those that broken down / absorbed slower.
  
  • To avoid sudden rise in glucose.

Question 10

Suggest why insulin can’t be taken as a tablet by mouth.

Answer 10

• Insulin is a protein.
• Would be hydrolysed by endopeptidases / exopeptidases.

Question 11

Describe how type II diabetes can be controlled.

Answer 11

• 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.

Question 12

Describe how you can evaluate the positions of health advisors and the food industry in relation to the increased incidence of type II diabetes.

Answer 12

• Consider both sides:
  
  • Health advisers aim - reduce risk of type II diabetes due to health problems caused.
    
    • So need to reduce obesity as it is a risk factor.
  • Food industry aim - maximise profit.