Control of blood glucose concentration (A-level only) Flashcards
It is important to maintain a stable blood glucose concentration for two reasons:
Meeting respiratory demands
Maintaining water potential
Meeting respiratory demands
Glucose is a respiratory substrate.
There must be enough glucose in the blood to meet the demands of respiring cells.
If glucose levels are too low, respiration rate will slow.
Maintaining water potential
Glucose can affect the water potential of the blood.
An increase in blood glucose concentration will decrease the water potential of the blood.
Water will move out of tissues into the blood by osmosis.
This causes dehydration of the cells and the cells will die.
Blood pressure also increases.
Factors affecting blood glucose levels:
Eating
Exercise
Eating
Eating carbohydrates causes an increase in blood glucose concentration.
Increases in blood glucose levels are monitored by the pancreas.
Exercise
Exercising causes a decrease in blood glucose concentration because glucose is being used in respiration to power muscle contraction.
Decreases in blood glucose levels are also monitored by the pancreas.
The liver
The liver is an organ that plays an important role in controlling blood glucose concentration.
The processes that take place in the liver are:
Glycogenesis
Glycogenolysis
Gluconeogenesis
Glycogenesis
When blood glucose concentration is too high, the liver cells produce enzymes that convert glucose into glycogen.
This glycogen is then stored in the liver cells.
This process is called glycogenesis.
Glycogenolysis
When blood glucose concentration is too low, the liver cells produce enzymes that break down the glycogen stored in the cells to glucose.
This process is called glycogenolysis.
Gluconeogenesis
When blood glucose concentration is too low, liver cells also form glucose from glycerol and amino acids.
This process is called gluconeogenesis.
Insulin
When blood glucose concentration increases above the optimum concentration (90mg 100cm−3), insulin returns the level to normal through negative feedback.
Stages of Insulin:
Detection by Beta-Cells
Secretion of insulin
Binding to muscle cells
Glycogenesis
Detection by Beta-Cells
High blood glucose concentration is detected by the beta (β) cells in the pancreas.
Beta cells are located in the islets of Langerhans.
Secretion of insulin
Beta cells respond to high blood glucose concentration by secreting a hormone called insulin into the blood.
Insulin travels in the blood to the liver and muscle cells.
Binding to muscle cells
Insulin binds to receptors on the muscle cell membranes.
The muscle cells insert more glucose channel proteins in the cell membrane.
This causes:
The rate of uptake of glucose by muscle cells to increase.
The rate of respiration in the muscle cells to increase.
Glycogenesis
Insulin binds to receptors on the liver cell membranes.
The liver cells produce enzymes that convert glucose to glycogen.
Glycogen is stored in the liver cells’ cytoplasm.
This process is called glycogenesis.
Importance of insulin
The role of insulin in lowering blood glucose concentration is important for maintaining an optimum blood water potential.
If blood glucose levels were not reduced by insulin, the blood water potential would decrease.
Water in the cells in the body would diffuse out, causing the cells to shrink and die.
Glucagon
When blood glucose concentration decreases below the optimum concentration (90mg 100cm−3), glucagon, like insulin, returns the level to normal through negative feedback.
Stages of Glucagon:
Detection by Alpha-cells
Secretion of glucagon
Glycogenolysis
Gluconeogenesis
Rate of respiration
Detection by Alpha-cells
Low blood glucose concentration is detected by the alpha (α) cells in the pancreas.
Alpha cells are located in the islets of Langerhans.
Secretion of glucagon
Alpha cells respond to low blood glucose concentration by secreting a hormone called glucagon into the blood.
Glucagon travels in the blood to the liver cells.
Glycogenolysis
Glucagon binds to receptors on the liver cell membranes.
The liver cells produce enzymes that convert glycogen to glucose.
This process is called glycogenolysis.
Gluconeogenesis
Binding of glucagon to liver cell membranes also causes the release of enzymes that form glucose from glycerol and amino acids.
This process is called gluconeogenesis.
Rate of respiration
Glucagon also slows the respiration rate in cells.
Slowing respiration slows the rate at which glucose is used up.
Importance of glucagon
The role of glucagon in increasing blood glucose concentration is important for survival.
If blood glucose levels were not increased by glucagon, there would not be enough glucose available for respiration.
If there is not enough glucose for respiration, there will be no energy available for survival.
Adrenaline
Adrenaline is a hormone that is secreted in response to low blood glucose concentration.
It is also released during exercise and in times of stress.
Stages in adrenaline:
Secreton of adrenaline
Binding to liver cells
Secretion of adrenline
Adrenaline is secreted from the adrenal gland in response to low blood glucose concentration, exercise and stress.
Binding to liver cells
Adrenaline binds to receptors on the liver cell membrane.
Adrenaline induces two reactions in the liver cells:
Activation of glycogenolysis (glycogen → glucose).
Inhibition of glycogenesis (glucose → glycogen).
Adrenaline also promotes secretion of glucagon from the pancreas and inhibits secretion of insulin.
Primary messengers
Primary messengers are messengers that do not enter a cell.
Primary messengers exert an action on the cell membrane by binding to receptors and triggering a change within the cell.
This change can be the activation of another molecule (a secondary messenger) or it may initiate a reaction.
Hormones are examples of primary messengers (e.g. adrenaline and glucagon).
Secondary messengers
Secondary messengers initiate and coordinate responses that take place inside a cell.
Secondary messengers are usually activated by the binding of a primary messenger to a cell surface receptor.
Cyclic AMP (cAMP) is an example of a secondary messenger.
Cyclic AMP
Cyclic AMP (cAMP) is a secondary messenger involved in the control of blood glucose concentration.
The steps involved in the cyclic AMP response are:
Primary messengers
Adenylate cyclase
cyclic AMP
Glycogenolysis
Primary messengers
Adrenaline or glucagon bind to receptors on the cell membranes of liver cells.
Adrenaline and glucagon are primary messengers because they do not enter the cell.
Adenylate Cyclase
Binding of adrenaline or glucagon activates an enzyme called adenylate cyclase.
Adenylate cyclase converts ATP to cyclic AMP (cAMP).
Cyclic AMP
cAMP activates an enzyme called protein kinase A.
Protein kinase A triggers a cascade of reactions that result in glycogenolysis.
Glycogenolysis
Glycogenolysis breaks down glycogen into glucose.
Type 1 diabetes
Type I diabetes sufferers cannot produce insulin.
Cause of type 1 diabetes
Type I diabetes is caused when the beta cells in the pancreas are attacked by the immune system.
The beta cells become damaged and can no longer produce insulin.
Some people are more genetically predisposed to type I diabetes than others.
It normally develops during childhood.
Hypoglycaemia
Eating causes the blood glucose concentration to increase.
People with type I diabetes cannot produce insulin to counteract the increased levels of glucose so the blood glucose level remains high.
This is called hyperglycaemia.
Hyperglycaemia can lead to death if it is not treated.
Controlling intake of glucose is also important to prevent a sudden increase in glucose levels.
Treatment for type 1 diabetes
Insulin therapy is used to treat type I diabetes.
Insulin is injected regularly during the day or an insulin pump can be used continuously.
Too much insulin can cause a fall in glucose levels called hypoglycaemia so insulin therapy must be carefully monitored.
Type 2 diabetes
Type 2 diabetes sufferers don’t produce enough insulin or cannot respond to insulin.
Type II usually develops later in life than type I.
Cause of type 2 diabetes
Type 2 diabetes is correlated with obesity, lack of exercise, age and family history.
Type 2 diabetes develops when the beta cells in the pancreas no longer produce enough insulin or when the muscle and liver cells stop responding to insulin.
Hyperglycaemia
Type 2 diabetes can lead to hyperglycaemia.
This is when blood glucose levels are higher than the optimum level.
Treatment for type 2 diabetes
Type 2 diabetes is treated by eating a healthy diet and exercising.
In some cases medication is used to lower glucose levels or in rare cases, insulin injections are used.
Preventing type 2 diabetes
Healthy lifestyle
Change4Life
Food content
Healthy lifestyle
Health advisors recommend a lifestyle that involves:
A balanced diet that is low in salt, fat and sugar.
Regular exercise.
Change4Life
The NHS ‘Change4life’ campaign has been introduced.
The campaign educates on how to lead a healthy lifestyle.
The campaign is designed to decrease the risk of developing type II diabetes.
Food content
The World Health Organisation (WHO) recommends that the food industry should help combat the rise in obesity and diabetes by:
Reducing levels of sugar, saturated fats and salt in processed food products.
Developing healthy, alternative products.
Having clear and simple labelling on food items showing the nutritional content (e.g. fat, sugar and salt content).
Promoting and market healthier foods, especially to children.
Colorimetry
Colorimetry is a technique used to identify the concentration of glucose in an unknown ‘urine’ sample.
Stages involved in colorimetry:
Prepare urine samples
Prepare calibration curve
Incubate test tubes
Use colorimeter
Recrord results
Prepare urine samples
Take three test tubes and label each with the name of the patient (urine sample).
Add three cm3 urine samples from each patient.
To each test tube add 2 cm3 of Benedict’s reagent and mix the contents of the tube.
Benedict’s reagent is used to detect the presence of glucose.
The reagent is blue and turns from blue to red when glucose concentration is greater.
The solution also becomes more opaque.
Prepare calibration curve
Label six test tubes 0 to 10 mmol dm−3.
A glucose solution of 10 mmol dm−3 is provided.
Dilute this standard glucose solution using distilled water to produce 5 additional concentrations which will be used to make the calibration curve.
The concentrations should be 0 mmol dm−3, 2mmol dm−3, 4mmol dm−3, 6mmol dm−3, 8mmol dm−3, and 10mmol dm−3.
Incubate test tubes
Add 2 cm3 of Benedict’s reagent to each tube and mix the contents.
Place all the test tubes into the water bath together (including the tubes with the urine samples) and time for four minutes.
Allow to cool before taking readings from the colorimeter.
Use colorimeter
Use the contents of the 0.0 mmol dm−3 glucose solution tube, which you have heated with Benedict’s, as a blank to calibrate the colorimeter to zero absorbance.
Place the remaining samples in cuvettes into the colorimeter and read the absorbance.
Record results
Record your results in a table and plot a graph of the absorbance of the known concentrations of glucose.
Plot concentration of glucose on the x-axis and absorbance on the y-axis.
Using the graph and the absorbance values obtained for the urine samples read off from the graph the concentration of glucose in the urine samples.
Record your results in a suitable table.
