Regulation of blood glucose

• why is it important to regulate blood glucose levels?


  • high concentration lowers water potential, so more water enters blood increasing blood pressure - can cause damage to capillaries
  • low concentration, slows metabolic processes, not enough ATP, fainting, fatigue, due to lack of sugar to the brain
  • really high - coma or death
• what is glycogenolysis?


  • glycogen stored in liver and muscle cells is broken down into glucose which is released into bloodstream, increasing blood glucose concentration
• what is glycogenesis?


  • the production of glycogen, when blood glucose concentration is too high, excess glucose is taken in through diet is converted into glycogen which is stored in liver
• what is gluconeogenesis?


  • the production of glucose from non-carbohydrate sources, e.g. liver able to make glucose from glycerol and amino acids, glucose released into bloodstream
• what are factors that increase blood glucose levels?


  • diet - carbohydrate rich food and sweet food, carbohydrates broken down release glucose into blood
  • glycogenolysis
  • gluconeogenesis
• what are factors that decrease blood glucose levels?

  • increases respiration rate - high levels of exercise means greater glucose demand
  • glycogenesis
  • starvation
• what are features of insulin?


  • made in Beta cells of Islets of Langerhans in pancreas
  • responds to high blood glucose concentration
  • virtually all body cells have insulin receptors
  • changes tertiary structure of glucose transporter protein
  • increase rate of glucose absorption
  • increase respiration rate
  • increase rate of glycogenesis - remove glucose from blood
  • inhibits release of glucagon from alpha cells
• what are the features of glucagon?


  • produced by Alpha cells in Islets of Langerhans in pancreas
  • responds to low blood glucose concentration
  • liver and fat cells have glucagon receptors
  • liver cells - glycogenolysis, increase gluconeogenesis
  • fat cells - hydrolysis of triglycerides (lipolysis)
• how is insulin removed from blood?


  • enzymes in liver break it down
• why are insulin and glucagon described as antagonistic?


  they work in opposite action of the primary hormone
• how does blood glucose fluctuate around a point?


  as a result of negative feedback
• what hormone can also affect blood glucose levels?


  adrenaline - in times of stress
• what effect does insulin have when it binds to receptor cells in muscle cells?


  • insulin binds to complementary receptor, causing conformational change of tertiary structure
  • part of receptor inside cell (tyrosine kinase) becomes phosphorylated which causes other enzymes to be phosphorylated
  • series of enzyme controlled reactions triggered
  • triggers GLUT4 vesicles to transport protein to attach and move along cytoskeleton to fuse with plasma membrane
  • GLUT4 transport protein makes membrane more permeable to glucose, which moves in by facilitated diffusion
• what happens in the beta cells when blood glucose levels are low?


  • lower levels of ATP inside cell
  • ATP-sensitive K+ channels in beta cell membrane are open
  • K+ ions diffuse out
  • inside cell is -70mV compared to outside
  • membrane is hyperpolarised
  • voltage gated Ca2+ channels remain closed
  • secretory vesicles containing insulin don't fuse with membrane (as exocytosis needs Ca2+)
  • insulin not secreted
• what happens in beta cells when blood glucose levels are high?


  • higher level of ATP inside cell
  • ATP sensitive K+ channel in beta cell membrane close
  • K+ ions aren't diffused out
  • inside cell is -30mV compared to the outside
  • membrane is depolarised
  • voltage gated Ca2+ channels open
  • secretory vesicles containing insulin attach and move along cytoskeleton to fuse with membrane (presence of Ca2+)
  • insulin secreted by exocytosis