Control of blood glucose concentration 3.6.4.2 ( Organisms respond to changes in their internal and external environments 3.6)

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 , gluconeogenesis

Answer 2

Glycogenesis = Converts glucose into glycogen
Glycogenolysis = Converts glycogen into glucose
Gluconeogenesis = Converts amino acids and / or glycerol into glucose

Question 3

Explain the action of insulin in decreasing blood glucose concentration

Answer 3

Beta cells in the islets of Langerhans in pancreas detect blood glucose concentration is too high so they secrete insulin :

• Attaches to specific receptors on cell surface membranes of target cells ( liver / muscle cells )
  1) This causes more glucose channel proteins to join cell surface membrane
  • Increasing permeability to glucose
  • So more glucose can enter by facilitated diffusion
  2) This also activates enzymes involved in conversion of glucose to glycogen ( glycogenesis )
  • Lowering glucose concentration in cells , creasing a concentration gradient
  • So glucose enters cells 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 so secrete glucagon :

• Attaches to specific receptors on cell surface membranes of target cells ( 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 messenger”) attach to specific receptors on cell membranes which :
1) activated enzyme adenylate cylcase ( changes shape)
2) Which converts many ATP to many cylic 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 type 1 and 2 diabetes

Answer 8

both = higher and uncontrolled blood glucose concentration; higher peaks after meals and remains high

Type 1 :
• B cells in islets of langerhans in pancreas produce insufficient insulin
• Normally develops in childhood due to an autoimmune response destroying beta cells in Islets of Langerhans

Type 2:
• Receptor (faulty) loses responsiveness / sensitivity to insulin but insulin still produced
• So fewer glucose transport proteins so less uptake of glucose so less conversion of glucose to glycogen
• Risk factor = obesity
••

Question 9

Describe how type 1 diabetes can be controlled

Answer 9

• Injections of insulin
• Blood glucose concentration monitored with biosensors ; dose of insulin matched to glucose intake
• Eat regularly and control carbohydrates intake e.g those that are 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 2 diabetes can be controlled

Answer 11

• Not normally treated with skin injections but maybe drugs which target insulin receptors to increase their sensitivity
- to increase glucose uptake by cells
• Reduce sugar intake
• Reduce fat intake - less glycerol converted to glucose
• more exercise - uses glucose by increasing respiration
• lose weight - increased sensitivity of receptors to insulin

Question 12

describe how you can evaluate the positions of health advisers and the food industry in relation to the increased incidence of type 2 diabetes

Answer 12

• Health advisors aim - reduce risk of type 2 diabetes due to health problems caused
- So need to reduce obesity as it is a risk factor
• Food industry aim - maximise profit