Hormonal

• Hormones


  Signalling molecules secreted by ductless endocrine glands, affect target cells with complementary receptors
• Exocrine gland


  Secretes substances into a duct which carries them to a target in the body
• Adrenal glands


  • Adrenal cortex produces mineralocorticoids and glucocorticoids, adrenal medulla secretes adrenaline
• Pancreas


  • Islets of Langerhans have endocrine function secreting insulin and glucagon, exocrine function secreting digestive enzymes
• Blood glucose regulation


  1. High glucose detected by beta cells, insulin secreted, insulin stimulates glucose uptake in liver, fat and muscle cells

  2. Low glucose detected by alpha cells, glucagon secreted, glucagon stimulates glycogen breakdown in liver
• Control of insulin secretion

  Glucose entry into beta cells causes ATP production, closing of potassium channels, depolarisation, calcium entry, insulin exocytosis
• Diabetes


  Type I - autoimmune destruction of beta cells, Type II - cells less responsive to insulin, treated by insulin, diet, monitoring
• Genetically engineered bacteria can produce human insulin for diabetes treatment
• Stem cells from pancreas could be used to treat type I diabetes by synthesising new beta cells
• Stem cell treatment for diabetes

  • Precursor pancreatic cells found in mouse pancreas, could be used to synthesise new beta cells to treat type I diabetes
• Control of insulin secretion

  1. B cells detect rise in blood glucose concentration

  2. B cells secrete insulin directly into bloodstream
• Insulin receptors


  • Virtually all body cells have them on their cell surface membrane (exception being red blood cells)
• Insulin binding to receptor

  1. Causes change in tertiary structure of glucose transport protein channels

  2. Causes channels to open

  3. Allows more glucose to enter cell
• Insulin breakdown


  Broken down by enzymes in liver cells
• Insulin secretion


  Begins within minutes of food entering body and may continue for several hours after eating
• Negative feedback control of insulin secretion

  1. As blood glucose concentration returns to normal, detected by beta cells of pancreas

  2. When falls below set level, beta cells reduce insulin secretion
• Negative feedback


  Ensures changes are reversed and returned to set level in any control system
• Mechanism of insulin secretion in response to high blood

  • High BGL = glucose enters beta cell and is metabolised, producing ATP
  • ATP binds to and closes k+ channels
  • K+ ions can no longer diffuse out = causing depolarisation
  • Depolarisation opens voltage-gated Ca2+ channels
  • Ca2+ ions enter cell and cause insulin-containing secretory vesicles to release insulin by exocytosis
• Why does low blood glucose level not trigger insulin secretion?

  Normal blood glucose = K channels in beta cell plasma membrane are open so K can diffuse out