Endocrine function

• • islets of Langerhans are dispersed among lobules of acini. The islets are formed of alpha and beta cells
• • Alpha cells secrete glucagon whereas the beta cells secrete insulin
  • beta cells are most abundant and are found in central portion of the islets
  • Alpha cells make up the outer portion of the islets
• • Alpha cells = secrete glucagon
  • beta cells = secrete insulin
• Endocrine function

  
• 1. K+ channels in plasma membrane are open. K+ diffuses out, so inside of cells is -70mv compared to outside
  2. If glucose levels are high, glucose enters the beta cells- facilitated diffusion
• 3. glucose is phosphorylated then metabolised to produce ATP - glycolytic pathway/ glycolysis

  4. presence of extra ATP makes K+ channels close
• 5. K+ cannot diffuse out, so the membrane potential reduces to only -30mv - membrane depolarises

  6. Ca2+ channels are normally closed. They open in response to the change in membrane potential. Ca2+ ions rush into the cell - voltage gated
• 7. The Ca2+ ions cause the vesicles to release insulin by exocytosis - insulin causes conversion of glucose into glycogen