Hormones and the regulation of blood glucose

1. Hormones and the regulation of blood glucose Aim:

2. Hormones • Chemical messenger • Endocrine glands secrete the hormone into the blood • Has its effect at a different site (target site) to where it is made • Fits into receptor molecules on target cells and is therefore specific to the target • Small soluble organic molecules that travels in blood plasma • Effective in low concentrations and effects generally long lasting • Released by glands

3. Second messenger mechanism • Bind to receptors on the cell surface membrane creating a hormone-receptor complex • Second messenger released within the cell causing a series of enzyme controlled reactions • Required response is produced

4. Importance of blood glucose levels • Main respiratory substrate (only energy source for brain cells) • Lack of glucose causes fainting • Normal level per 100cm3 of blood is 90mg but can vary between 70-150mg

5. Sources of blood glucose • Diet – glucose released from breakdown of other carbohydrates eg starch, maltose, lactose and sucrose • Break down of glycogen – Broken down in the liver or muscles cells • Gluconeogenesis – Production of new glucose molecules from non-carbohydrates eg glycerol and amino acids

6. Involves 6 hormones • 2 negative feedback systems • Rise – hyperglycaemia stimulates insulin secretion • Decrease –hypoglycaemia inhibits insulin secretion

7. Factors influencing blood glucose levels • When eating takes place and the types of food eaten • The amount of physical and mental activity • The presence of 3 hormones … insulinglucagon and adrenaline

8. Insulin • Globular protein made up of 51 aa • Released by the islets of langerhans β cells in the pancreas in response to high blood sugar levels

9. Effects of insulin • Binds to the glycoprotein receptors found on almost all body cells, increasing absorbtion of glucose into cells (especially muscle cells) by the following mechanisms • The binding to receptors changes the structure of glucose transport protein channels (channels open) • An increase in number of carrier molecules in the membrane • Increases rate of respiratory processes lowering the cell glucose levels, therefore leading to a greater intake of glucose

10. Effects of insulin • Activates enzymes that convert glucose to glycogen (glycogenesis) in liver and muscle cells Glucose glucose phosphate glycogen • Increases conversion of glucose to fat Insulin

11. Glucagon • Released by islet of Langerhans α cells the pancreas in response to low blood glucose levels • Activates the enzyme phosphorylase • The phoshorylase enzyme catalyses the breakdown of glycogen in the liver (glycogenolysis) Glycogen glucose phosphate glucose phosphorylase

12. Glucagon • Stimulates the synthesis of glucose from glycerol and amino acids (gluconeogenesis) Glycerol  glucose Amino acids  glucose

13. Adrenalin • Adrenalin released by the adrenal medulla in times of danger, stress and cold. • Stimulates conversion of glycogen to glucose (glycogenolysis) by activating an enzyme • Stimulates the synthesis of glucose from glycerol and amino acids (gluconeogenesis) • Inactivates an enzyme that synthesises glycogen from glucose

14. The role of the liver • The liver is the site where the following processes occur Glycogenesis - (glucose to glycogen) Gluconeogenesis (amino acids/glycerol to glucose Glycogenolysis (glycogen to glucose)

15. Role of the pancreas • Produces insulin and glucagon • Islets of Langerhans β cells – Detect high glucose levels - produce insulin • Islets of Langerhans α cells – Detect low glucose levels - produce glucagon

16. The factors that influence blood glucose concentration. • The role of the liver in glycogenesis and gluconeogenesis. • The role of insulin and glucagon in controlling the uptake of glucose by cells and in • activating enzymes involved in the interconversion of glucose and glycogen. The • effect of adrenaline on glycogen breakdown and synthesis. • The second messenger model of adrenaline and glucagon action. • Types I and II diabetes and control by insulin and manipulation of the diet.

17. TASK • Research and presentation of findings on Type I and Type II diabetes and how they can be controlled by insulin and diet.