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 eg. 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

Role of liver in Glycogenesis

Answer 3

Converts glucose → glycogen

Question 4

Role of liver in Glycogenolysis

Answer 4

Converts glycogen → glucose

Question 5

Role of liver in Gluconeogenesis

Answer 5

Converts amino acids and/or glycerol → glucose

Question 6

Explain the action of insulin in decreasing blood glucose concentration

Answer 6

• Beta cells in islets of Langerhans in pancreas detect blood glucose concentration is too high → secrete insulin:

● The 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
   > decreasing the glucose concentration in the blood

Question 7

Explain the action of glucagon in increasing blood glucose concentration

Answer 7

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

● Glucagon Attaches to specific receptors on cell surface membranes of target cells eg. liver which:
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 (higher in cells than blood)→ glucose enters blood by facilitated diffusion

Question 8

Explain the role of adrenaline in increasing blood glucose concentration

Answer 8

● 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

Question 9

What may cause the adrenal glands to secrete adrenaline?

Answer 9

Fear / stress / exercise

Question 10

Describe the second messenger model of adrenaline and glucagon action

Answer 10

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

1. Activates enzyme adenylate cyclase (it changes shape)
2. Which then 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 11

Suggest an advantage of the second messenger model

Answer 11

● 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 12

What is the same about type 1 and type 2 diabetes?

Answer 12

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

Question 13

Type I diabetes

Answer 13

• 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

Question 14

Type II diabetes

Answer 14

• 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

Question 15

Describe how of type I diabetes can be controlled

Answer 15

● 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

Question 16

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

Answer 16

● Insulin is a protein
● Would be hydrolysed by endopeptidases / exopeptidases in stomach/saliva

Question 17

Describe how of type II diabetes can be controlled

Answer 17

● 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 18

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

Answer 18

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