blood glucose control

• beta cells: secrete insulin
• alpha cells: secrete glucagon
• islets of langerhans: clusters of cells in the pancreas that produce insulin and glucagon
• insulin:

  • activates enzymes in liver than convert glucose into glycogen
  • increases rate of respiration to use up glucose
• glucagon:

  • activates enzymes in liver cells that break glycogen into glucose
  • activates enzymes that form glucose from glycerol and amino acids
  • decreases rate of respiration
• response to high blood glucose:

  • pancreas detects concentration too high
  • beta cells secrete insulin, alpha cells stop secreting
  • insulin binds to receptors on liver and muscle cells
  • cells take up more glucose
  • activates glycogenesis
  • more respiration
• response to low blood glucose:

  • pancreas detects level too low
  • alpha cells secrete glucagon, beta cells stop secreting
  • glucagon binds to receptors on liver cells
  • glycogenolysis activated
  • gluconeogenesis activated
  • cells respire less
• glycogenesis: forming glycogen from glucose
• glycogenolysis: breaking down glycogen
• gluconeogenesis: forming glucose from non-carbohydrates
• glucose transporters:

  • GLUT4 is a glucose transporter in skeletal and cardiac muscle cells
  • when insulin levels are low, GLUT4 is stored in vesicles in the cytoplasm of cells
  • insulin binds to receptors on the membrane, triggering movement of GLUT4 to the membrane
  • glucose is then transported in via facilitated diffusion
• adrenaline is secreted when:

  • low blood glucose
  • stressed
  • exercising
• effect of adrenaline on blood glucose:

  • activates glycogenolysis
  • inhibits glycogenesis
  • activates glucagon secretion
  • inhibits insulin secretion
  • makes more glucose available for muscles to respire
• second messenger model:

  • receptors for adrenaline and glucagon have specific tertiary structures
  • adrenaline and glucagon bind to their receptors and activate adenylate cyclase
  • this converts ATP into a chemical signal, cyclic AMP (cAMP)
  • cAMP activates protein kinase A
  • this activates glycogenolysis through a series of chain reactions
• hyperglycemia: high blood glucose
• hypoglycemia: low blood glucose
• type 2 diabetes:

  • linked with obesity
  • acquired later in life
  • beta cells don't produce enough insulin, or cells don't respond properly to insulin
• diabetes mellitus (type 1):

  • immune system attacks beta cells
  • treated with insulin therapy