Control of Blood Glucose Concentration

Describe the factors that influence blood glucose concentration

• Consumption of carbohydrates (glucose absorbed into blood)

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

What is the role of the liver in glycogenesis?

Converts glucose into glycogen

What is the role of the liver in glycogenolysis?

Converts glycogen into glucose

What is the role of the liver in gluconeogenesis?

Converts amino acids and/or glycerol into glucose

Explain the action of insulin in decreasing blood glucose concentration

The beta cells in islets of Langerhans in pancreas detect if the blood glucose concentration is too high, and secretes insulin

• Insulin attaches to specific receptors on cell surface membranes of target cells e.g. liver/ muscles

• This causes more glucose channel proteins to join cell surface membrane, which increases permeability to glucose, and more glucose can enter by facilitated diffusion

• This also activates enzymes involved in the glycogenesis- the conversion of glucose to glycogen, lowering the glucose concentration in cells will create a concentration gradient so glucose can enter the cells via facilitated diffusion

Explain the action of glucagon in increasing blood glucose concentration

Alpha cells in islets of Langerhans in pancreas detects if blood glucose concentration is too low, and will secrete glucagon

• Glucagon attaches to specific receptors on cell surface membrane of target cells e.g. liver

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

• It also activates enzymes involved in conversion of glycerol/ amino acids to glucose (gluconeogenesis)

• This establishes a concentration gradient, so glucose enters blood by facilitated diffusion

Explain the role of adrenaline in increasing blood glucose concentration

In fear/ stress/ exercise, adrenal glands secrete adrenaline

• The adrenaline attaches to the specific receptors on the cell surface membranes of target cells e.g. liver

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

• This establishes a concentration gradient, so glucose enters blood via facilitated diffusion

Describe the second messenger model of adrenaline and glucagon action

Adrenaline/ glucagon (first messengers) attach to specific receptors on cell membrane which

• This changes the shape of the receptor protein, which spans the phospholipid bilayer

• This change in tertiary structure of the protein activates the enzyme adenylate cyclase, which converts ATP to cyclic AMP

• Cyclic AMP acts as the second messenger, and takes effect by activating protein kinase enzymes

• Protein kinases activate enzymes to break down glycogen to glucose, which enters the blood

What is an advantage of the second messenger model?

• Amplifies signal from hormone

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

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

What is similar about type 1 and type 2 diabetes?

Both have higher and uncontrolled blood glucose concentration, high peaks after meals and remains high

What are the causes of type 1 diabetes?

• Beta cells in islets of Langherhans in pancreas produce insufficient insulin

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

What is the cause of type 2 diabetes?

• Glycoprotein receptors loses responsiveness/ sensitivity to insulin, but inadequate supply of insulin from pancreas

• So fewer glucose transport protein join cell surface membrane and there is less uptake of glucose, so less conversion of glucose to glycogen and glucose cant enter cells from blood via facilitated diffusion= high blood glucose concentration

How can type 1 diabetes be controlled?

• Injections of insulin as pancreas does produce enough

• Blood glucose conc monitored with biosensors; dose of insulin matched to glucose intake

• Eat regularly and control carbohydrate intake, to avoid sudden rise in glucose

Why can’t insulin be taken as a tablet?

Insulin is a protein, so would be hydrolysed by endo/exopeptidases

Describe how type 2 diabetes can be controlled

• May use drugs which target insulin receptors to increase their sensitivity and therefore increase glucose uptake by cells

• Reduce sugar intake

• Reduces fat intake

• More exercise, uses glucose/ fats by increasing respiration

• Lose weight; increase sensitivity of receptors to insulin