The regulation of blood glucose

1. 05/01/2020 The regulation of blood glucose • Starter: • Write down as many things as you can think about that affect your blood sugar levels

2. Objectives • Explain how hormones work • Outline the role of the pancreas as an endocrine gland • Explain how blood glucose concentration is regulated with reference to insulin, glucagon and adrenaline

3. Hormone Regulation • Negative feedback • Regulation of blood sugar is a good example of this. • The hormones involved include insulin, glucagon and adrenaline.

5. The pancreas • Is both an endocrine and exocrine gland • Exocrine function - secretes digestive enzymes into the pancreatic duct • Endocrine function - secretes hormones (insulin and glucagon) directly into the blood

6. Secretion of enzymes (exocrine function) • Pancreatic cells surround small tubules which drain into the pancreatic duct • Pancreatic cells produce pancreatic juice which is made up of: • Amylase (a carbohydrase) • Trypsinogen (an inactive protease) • Lipase

7. Secretion of hormones (endocrine function) • Hormones are secreted from the cells in the islets of Langerhans • α cells manufacture and secrete the hormone glucagon • βcells manufacture and secrete the hormone insulin • These are released directly into the blood

8. Control of blood glucose The natural sources of blood glucose are: • Directly from the diet – glucose enters blood when carbohydrates are broken down • Breakdown of glycogen (Glycogenolysis) • Gluconeogenesis – production of new glucose from sources other than carbohydrates

9. Control of blood glucose • Is a negative feedback process • The normal blood glucose level is 90mg per 100ml of blood • If the blood glucose levels get too high or too low, then the changes are detected by the α and β cells in the islets of Langerhans.

10. Insulin and the β cells of the pancreas • *β cells act as receptors that detect a rise in blood glucose. • *When the rise is detected they secrete insulin into the blood plasma. • *Insulin binds to glycoprotein receptors on the cell surface of most body cells (notably excluding red blood cells). http://www.medbio.info/horn/time%203-4/insulin's%20mechanism%20of%20action.htm

11. Effects of insulin on target cells: 1. Vesicles containing glucose carrier proteins are stimulated to move to, and fuse with, the cell membrane. 2. More glucose is taken up by the cell. 3. Enzymes that convert glucose to glycogen (and fat) are activated.

12. The result… Increased rate of conversion of glucose to glycogen (glycogenesis) in the liver and muscles.

13. http://www.youtube.com/watch?v=X0ezy1t6N08

14. Glucagon and the α cells of the pancreas • *Act as receptors that detect a fall in blood glucose level. • *When a fall is detected they secrete the hormone glucagon into the blood plasma. • *Glucagon binds to glycoprotein receptors on LIVERcells only.

15. When bound the following happens: An enzyme is activated that converts glycogen to glucose (GLYCOGENOLYSIS). There is an increase in the conversion of amino acids and glycerol into glucose (GLUCONEOGENESIS). This results in an increase in blood glucose levels.

16. The role of adrenaline • There are a number of other hormones that increase blood sugar levels. The most well known is adrenaline. • Produced in adrenal glands (above kidneys) • It raises blood glucose by: • Activating an enzyme that causes breakdown of glycogen to glucose in the liver. • Inactivating an enzyme that synthesises glycogen from glucose.

17. Adrenaline • Hormone produce by the adrenal gland • Increases metabolic rate • Prepares the body for activity • Is an amino acid derivative • Cannot enter the target cell • Therefore it must cause an effect without entering the cell

18. Action of adrenaline (1)

19. Action of adrenaline (2)

20. Action of adrenaline (3)

21. First and second messengers • First messenger • A hormone that transmits a signal around the body • Second messenger • Is cAMP which transmits a signal inside the cell

22. The Second Messenger Model • Insulin binds to receptors, causing direct effects on the cell. • Adrenaline and glucagon use a second messenger model. • When they bind with receptors, an enzyme within the cell is activated to convert ATP to cyclic AMP. • cAMP then activates more enzymes within the cell. • Cyclic AMP is the SECOND MESSENGER.

23. Hormone interaction in regulating blood glucose Uses negative feedback as both hormones work to keep blood glucose at around 90mg per 100ml of blood. They are said to work antagonistically.

24. Task • The exam questions

25. Diabetes – type 1 Diabetes mellitus is a disorder that affects the body’s ability to regulate blood glucose levels. There are two different types – type 1 and type 2. Type 1 diabetes, also known as insulin-dependentdiabetes, normally occurs suddenly in childhood. The body is not able to produce its own insulin. This is thought to be caused by the immune system attacking the insulin-producing beta cells. Type 1 diabetes can be controlled with regular insulin injections and the careful management of diet and exercise.

26. Diabetes – type 2 Type 2 diabetes, also known as insulin-independentdiabetes, occurs mainly in people over 40, however it is becoming increasingly common in adolescents. This condition is caused by glycoprotein receptors on the body cells losing their responsiveness to insulin, or an inadequate supply of insulin from the pancreas. Type 2 diabetes can be controlled by careful regulation of diet and exercise.

27. What happens if glucose is not regulated? If the body does not regulate blood glucose concentration, it can become too high or too low, causing serious problems. Hyperglycaemia occurs when the blood glucose concentration becomes too high. This can lower the water potential of the blood, which can create osmotic problems that can cause dehydration. Symptoms include thirst, frequent urination, glucose in the urine and ultimately coma. Hypoglycaemia occurs when the blood glucose concentration becomes too low. This can occur when there is no store of glycogen. It can result in cells being deprived of energy. Symptoms include nausea, loss of concentration and ultimately coma.