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Control, Coordination and Feedback

Control, Coordination and Feedback. Blood glucose control. What is glucose? Why is glucose in the blood? Where does it come from? Where does it go? What is it there for? How much is there? How do you measure it? When does the concentration increase? When does the concentration decrease?.

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Control, Coordination and Feedback

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  1. Control, Coordination and Feedback

  2. Blood glucose control • What is glucose? • Why is glucose in the blood? • Where does it come from? • Where does it go? • What is it there for? • How much is there? • How do you measure it? • When does the concentration increase? • When does the concentration decrease?

  3. Blood glucose regulation

  4. Glucose concentration 80 to 120 mg 100 cm-3 blood This is the ‘normal’ range The concentration fluctuates Below 60 mg 100 cm-3 – coma Above 180 mg 100 cm-3 exceeds renal threshold and glucose appears in the urine

  5. Blood glucose What goes wrong when the concentration decreases? What goes wrong when the concentration increases?

  6. Blood glucose What goes wrong when the concentration decreases too far? Hypoglycaemia The symptoms associated with low blood sugar are: tiredness, confusion, dizziness, headaches, mood swings, muscle weakness, shaking

  7. Blood glucose What goes wrong when the concentration increases too far? Hyperglycaemia The symptoms include: Excessive thirst; frequent urination; fatigue; unexplained weight loss; vision problems, such as blurring; increased susceptibility to infections such as thrush.

  8. Blood glucose concentration • Keep within narrow limits • Corrective action if it increases • Corrective action if it decreases • Control mechanism needs to respond to fluctuations • Negative feedback • reduces the difference between actual and ideal / norm / set point

  9. Feedback system • Input • Receptor • Control centre • Effector(s) • Communication system • Corrective actions • Negative feedback

  10. Liver cells Binucleate cell central vein

  11. Liver cell

  12. Liver cell protein metabolism lipid metabolism carbohydrate metabolism

  13. Carbohydrate metabolism • glucose absorbed across membrane by facilitated diffusion • glucose stored as glycogen • glucose  glucose 6 phosphate • glucose 6 phosphate  glucose 1 phosphate • glucose units added onto end of glycogen molecule (glycosidic links) • glycogen synthetase

  14. Carbohydrate metabolism • glycogen broken down to glucose • glucose 1 phosphate molecules formed • glucose phosphorylase • glucose 1 phosphate  glucose 6 phosphate • glucose 6 phosphate to glucose • glucose diffuses out of cell through protein carriers

  15. Glucose storage • glucose concentration in blood increases • beta cells in pancreas release insulin • insulin stimulates liver cells to store glucose as glycogen • insulin stimulates lipid synthesis • insulin stimulates protein synthesis • insulin helps to conserve resources

  16. Islet of Langerhans endocrine tissue exocrine tissue

  17. Alpha cells Beta cells

  18. Structure of insulin

  19. Insulin receptor

  20. Secondary messengers • Glucagon and insulin are both proteins • Do not cross membranes • Signalling transduction at cell membrane • Secondary messenger produced inside membrane • 2o messenger transmits signal to enzymes within cytoplasm

  21. Cyclic AMP • Produced just inside cell membrane • ATP  cyclic AMP • Catalysed by Adenylate cyclase • Cyclic AMP combines with a protein • Starts a ‘chain reaction’ following stimulation by glucagon

  22. Amplification • Quick response required from many enzymes • Signal is amplified • Chain reaction: A  B  C  D • Enzyme cascade • Final enzyme converts glycogen  glucose

  23. Glucagon

  24. Glucagon

  25. Insulitis

  26. Modern technology Biosensor Insulin mini-pump

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