Glucose regulation

• Endocrine system and regulation

  Regulation of body temperature, blood glucose and water balance in animals by homeostatic mechanisms, including stimulus-response models, feedback loops and associated organ structures
• Malfunctions in homeostatic mechanisms

  Type 1 diabetes, hypoglycaemia, hyperthyroidism
• Adaptation


  • An inherited characteristic that increases an organism's chance of survival
  • There are 3 types: structural, physiological and behavioural
• Structural adaptation


  The physical characteristics of an organism (e.g. long neck of a giraffe)
• Physiological adaptation

  The internal biological function of an organism (e.g. shivering when cold)
• Behavioural adaptation


  Changes of patterns of behaviour that an organism makes in response to stimuli (e.g. a bird singing to attract a mate)
• Homeostasis

  The maintenance of a relatively stable internal environment within narrow limits despite varying environmental factors
• Signalling molecules


  Neurotransmitters (nervous system) and hormones (endocrine system)
• Stimulus-response model


  1. Stimulus

  2. Receptor

  3. Control centre (Modulator)

  4. Effector

  5. Response
• Stimulus-response example


  • Stimulus: seeing a drink
  • Receptor: eyes
  • Control centre: CNS
  • Effector: arm muscles
  • Response: movement of muscles (in order to drink)
• Negative feedback


  The response counteracts (diminishes) the stimulus
• Positive feedback


  The response increases the stimulus
• Negative feedback example


  • If cold, you start to shiver so that you can warm up
• Temperature regulation

  1. To lose heat: sweat, move to shade, small animals have high SA:V

  2. To gain heat: shivering, arterioles constrict, put on more clothes
• Glucose regulation


  Glucose levels in the blood rise and fall due to eating carbohydrates, using glucose, exercise, starvation, low carb diet, hormone activity involving insulin and glucagon
• Normal range of glucose

  3.0-7.7 mmol per Litre
• Insulin


  Produced by the beta cells of the islets of Langerhans (pancreas), lowers the overall concentration of glucose in the bloodstream by allowing glucose to enter cells, converts glucose to glycogen and stores in liver & fat if glucose levels are high, inhibits the conversion of glycogen to glucose
• Glucagon


  Produced by the alpha cells in the islets of Langerhans (pancreas), prevents the blood glucose level from falling too low, stimulates the liver to convert glycogen to glucose, inhibits the production of insulin
• If there is too much glucose in the blood


  Insulin converts some of it to glycogen
• If there is not enough glucose in the blood

  Glucagon converts some glycogen into glucose
• Effect of insulin

  Insulin attaches to receptors in cells in muscle, liver and fat, causes facilitated transport channels to open and allow entry of large amounts of glucose, promotes cellular respiration, storage as glycogen and fatty acids, inhibits glucagon
• Effect of glucagon


  Attaches to receptors in muscle, liver and fat cells, causes glycogen to be broken down in liver and muscle, breaks down stored fat into fatty acids for energy, converts amino acids into glucose in muscle, inhibits insulin
• If there is too much glucose in the blood, insulin converts some of it to glycogen
• If there is not enough glucose in the blood, glucagon converts some glycogen into glucose
• Stimulus-response model summary

  Stimulus, receptor, control centre (modulator), effector, response
• Diabetes


  Type 1 - insulin not produced, Type 2 - insulin resistance
• In diabetes


  The glucose in the blood increases, but there is no insulin to convert it into glycogen
• Gestational diabetes