Biology - 6.4.2 Control of blood glucose

Describe the factors that influence blood glucose concentration

• Consumption of carbohydrates → glucose absorbed into blood

• Rate of respiration (increases during exercise due to muscle contraction)

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

Glycogenesis

• Converts glucose → glycogen

Glycogenolysis

• Converts glycogen → glucose

Gluconeogenesis

• Converts amino acids / glycerol → glucose

Explain the action of insulin in decreasing blood glucose concentration

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

Insulin attaches to specific receptors on cell surface membranes of target cells (liver / muscles)

1. Causes more glucose channel proteins to join cell surface membrane

   • Increasing permeability to glucose

   • So more glucose can enter cell by facilitated diffusion

2. Also activates enzymes involved in the conversion of glucose to glycogen (glycogenesis)

   • Lowering glucose concentration in cells, creating a concentration gradient

   • So glucose enters the cell by facilitated diffusion

Explain the action of glucagon in increasing blood glucose concentration

Alpha cells in islet of Langerhans in pancreas detect blood glucose concentration is too low → 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)

Establishes a concentration gradient → glucose enters blood by facilitated diffusion

Explain the role of adrenaline in increasing blood glucose concentration

Fear/ stress/ exercise → adrenal glands secrete adrenaline

Attaches to specific receptors on cell surface membranes of target cells (liver)

• Activates enzymes involved in hydrolysis of glycogen to glucose (glycogenolysis)

  • 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

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 (glycogenolysis)

Suggest an advantage of the second messenger model

• Amplifies signal from hormone

• As each hormone can stimulate production of many molecules of many second messenger (cAMP)

• Which can in turn activate many enzymes for rapid increase in glucose

Compare the causes of types l and ll diabetes

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

Type l

• Beta cells in islets of Langerhans produce insufficient insulin

• Normally develops in childhood due to an autoimmune response destroying beta cells

Type ll

• Receptor (faulty) loses responsiveness / sensitivity to insulin (still produced)

• So fewer glucose transport proteins → less uptake of glucose → less conversion of glucose into glycogen (glycogenesis)

• Risk factor = obesity

Describe how Type l 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 (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 Type ll diabetes can be controlled

• Not normally treated with insulin injections, may use drugs which target insulin receptors to increase sensitivity

  • To increase glucose uptake by cells

• Reduce sugar intake (carbohydrates) → less absorbed

• Reduce fat intake → less glycerol converted to glucose

• More (regular) exercise → use glucose by inc. respiration

• Lose weight → increased sensitivity of receptors to insulin