Blood Glucose Concentration

• Blood glucose concentration is at a set point of 90mg/100cm3 blood
• • Islets of Langerhans: tissue that acts as both receptors and endocrine cells 
• Blood Glucose Conc. Too High 

  1. Beta cells in Islet of Langerhans detect high glucose levels and secret insulin into the bloodstream 
  2. Insulin binds to receptor on surface of cells 
  3. Causes carrier/channel proteins to open and more glucose transporters to be formed in the cell membrane by vesicle fusion, increasing rate of glucose uptake by facilitated diffusion 
  4. Causes signalling cascade resulting in activation of glycogen synthase, increasing glycogenesis in muscle and liver cells
  5. Respiration Increases to use up more glucose
  6. Excess glucose may also undergo lipogenesis
• Blood Glucose Conc. Too Low

  1. Alpha cells in the Islet of Langerhans detect low glucose levels and release glucagon into the bloodstream 
  2. Glucagon binds to receptor on surface of liver cells 
  3. Receptor activates membrane-bound enzyme adenylate cyclase 
  4. This catalyses conversion of ATP to cAMP - a second messenger 
  5. cAMP activates a protein kinase  
  6. The protein kinase activates enzymes that cause glycogenolysis 
  7. When glucose levels are very low, can also result in gluconeogenesis
• • Adrenaline is released (as part of the fight or flight response) from the adrenal glands 
  • Adrenaline binds to different receptors to glucagon, on muscle cells, but activates the same response as glucagon 
  • Provides glucose for rapid energy release
• Glycogenesis: the process of excess glucose being converted to glycogen when blood glucose is higher than normal
• Glycogenolysis: the hydrolysis of glycogen back into glucose in the liver. This occurs when blood glucose levels are lower than normal 
• Lipogenesis: glucose converted into lipids
• Gluconeogenesis: Synthesis of glucose from lipids, amino acids, or nucleic acids
• Symptoms of diabetes

  • High thirst - due to osmosis of water from the cells to the blood which has a lower water potential 
  • Excessive urine production - due to excess water in blood 
  • Tiredness - due to loss of glucose in urine and poor uptake of glucose by muscle and liver cells 
• Type 1 diabetes

  • Insulin deficiency due to autoimmune killing of Beta Cells
  • Controlled by monitoring diet/blood sugar/Injecting insulin
  • Often hereditary
  • The amount of insulin needed is affected by diet and physical activity
• Type 2 diabetes

  • Insulin is produced but insulin receptors in the target cells less responsive
  • Glucose stays in the blood
  • Associated with obesity
  • Controlled by diet and exercise