Glucose

• Glucose concentration in the blood

  Normally around 90 mg per 100 cm³ of blood
• Monitoring of blood glucose concentration

  Cells in the pancreas monitor it
• Blood glucose concentration rises


  After eating food containing carbohydrate
• Blood glucose concentration falls


  After exercise, as more glucose is used in respiration to release energy
• Hormonal control of blood glucose concentration

  Using two hormones: insulin and glucagon
• Insulin and glucagon

  • Chemical messengers that travel in the blood to their target cells (effectors)
  • Secreted by clusters of cells in the pancreas called the islets of Langerhans
• Beta (ß) cells and alpha (a) cells


  • Beta cells secrete insulin into the blood
  • Alpha cells secrete glucagon into the blood
• Insulin lowering blood glucose concentration


  1. Binds to receptors on muscle and liver cells

  2. Increases permeability of muscle-cell membranes to glucose, so cells take up more glucose

  3. Activates enzymes in muscle and liver cells that convert glucose into glycogen

  4. Increases rate of respiration of glucose, especially in muscle cells
• Glucagon raising blood glucose concentration


  1. Binds to receptors on liver cells

  2. Activates enzymes that break down glycogen into glucose
• Glycogenesis


  The process of forming glycogen from glucose
• Glycogenolysis


  The process of breaking down glycogen into glucose
• Glucagon activates enzymes involved in the formation of glucose from glycerol and amino acids


  Gluconeogenesis
• Glucagon

  Decreases the rate of respiration of glucose in cells
• Hormones travel in the blood to their target cells


  Responses produced by hormones are slower than those produced by nervous impulses
• Hormones are not broken down as quickly as neurotransmitters


  Their effects tend to last for longer
• Negative feedback mechanisms


  Keep blood glucose concentration normal
• Rise in blood glucose concentration

  1. Pancreas detects high blood glucose

  2. B cells secrete insulin

  3. A cells stop secreting glucagon

  4. Insulin binds to liver and muscle cells

  5. Liver and muscle cells respond to decrease blood glucose

  6. Blood glucose returns to normal
• Fall in blood glucose concentration

  1. Pancreas detects low blood glucose

  2. A cells secrete glucagon

  3. B cells stop secreting insulin

  4. Glucagon binds to liver cells

  5. Liver cells respond to increase blood glucose

  6. Blood glucose returns to normal
• Glucose transporters

  Channel proteins which allow glucose to be transported across a cell membrane
• GLUT4

  • Glucose transporter found in skeletal and cardiac muscle cells
  • Stored in vesicles in the cytoplasm when insulin levels are low
  • Moves to the cell membrane when insulin binds to receptors, allowing glucose transport into the cell by facilitated diffusion
• Adrenaline


  • Hormone secreted from adrenal glands when there's low blood glucose, stress, or exercise
  • Binds to receptors in liver cell membranes
• Adrenaline's effects on blood glucose

  1. Activates glycogenolysis (breakdown of glycogen to glucose)

  2. Inhibits glycogenesis (synthesis of glycogen from glucose)

  3. Activates glucagon secretion

  4. Inhibits insulin secretion
• Second messengers

  Chemicals produced inside the cell that transmit the signal from a hormone binding to a receptor on the cell surface
• Second messenger model

  1. Hormone binds to receptor on cell surface

  2. Activates enzyme on inside of cell membrane

  3. Enzyme produces second messenger

  4. Second messenger activates other enzymes to bring about response
• Adrenaline and glucagon receptors

  • Have specific tertiary structures complementary to their respective hormones
  • Binding activates adenylate cyclase enzyme
  • Activated adenylate cyclase converts ATP to cyclic AMP (cAMP)
  • cAMP activates protein kinase A
  • Protein kinase A activates cascade that breaks down glycogen to glucose (glycogenolysis)
• Diabetes mellitus

  A condition where blood glucose concentration can't be controlled properly
• Types of diabetes


  • Type I
  • Type II
• Type I diabetes

  • The immune system attacks the B cells in the islets of Langerhans so they can't produce any insulin
  • After eating, the blood glucose level rises and stays high — this is called hyperglycaemia and can result in death if left untreated
  • The kidneys can't reabsorb all this glucose, so some of it's excreted in the urine
  • Treated with insulin therapy
• Insulin therapy for Type I diabetes

  • Most people need regular insulin injections throughout the day
  • Some use an insulin pump to deliver insulin continuously
  • Insulin therapy has to be carefully controlled because too much can produce a dangerous drop in blood glucose levels — this is called hypoglycaemia
  • Eating regularly and controlling simple carbohydrate intake (intake of sugars) helps to avoid a sudden rise in glucose
• No one knows exactly what causes the immune system to attack the ß cells and cause Type I diabetes
• Scientists have found that some people have a genetic predisposition to developing Type I diabetes
• Scientists think the disease may be triggered by a viral infection
• Type II diabetes


  • Usually acquired later in life than Type I
  • Often linked with obesity
  • More likely in people with a family history of the condition
  • Other risk factors include lack of exercise, age and poor diet
  • Occurs when the ß cells don't produce enough insulin or when the body's cells don't respond properly to insulin
  • Cells don't respond properly because the insulin receptors on their membranes don't work properly, so the cells don't take up enough glucose
  • This means the blood glucose concentration is higher than normal
  • Can be treated by eating a healthy, balanced diet, losing weight (if necessary) and regular exercise
  • Glucose-lowering medication can be taken if diet and exercise can't control it
  • Eventually, insulin injections may be needed
• Type II diabetes is becoming increasingly common in the UK
• This has been linked to increasing levels of obesity, a move towards more unhealthy diets and low levels of physical activity
• Type II diabetes can cause additional health problems, including visual impairment and kidney failure
• Response of health advisors to reduce the risk of Type II diabetes

  • Recommend people eat a diet that's low in fat, sugar and salt, with plenty of whole grains, fruit and vegetables
  • Take regular exercise
  • Lose weight if necessary
• NHS's 'ChangeLife' campaign

  Aims to educate people on how to have a healthier diet and lifestyle, and so reduce their risk of developing conditions like Type II diabetes
• Health advisors

  • Have challenged the food industry to reduce the advertising of junk food (particularly to children)
  • Improve the nutritional value of their products
  • Use clearer labelling on products - allowing consumers to make healthier choices about what to buy
• Response of food companies

  Some have attempted to make their products more healthy, e.g. by using sugar alternatives to sweeten food and drinks, and by reducing the sugar, fat and salt content of products