2. The Pancreas By Margaret Sheekey

3. Histology of the Pancreas The pancreas is in the abdomen, just below the stomach It is to the right of the liver when viewed from the front It is both an exocrine and an endocrine organ

4. Pancreas-Exocrine Function  Exocrine- Glands that secrete chemicals through ducts into cavities or surfaces on the body  Most of the pancreas is exocrine tissue – These are called the acinar cells  The acinar cells are found in clusters around the pancreatic duct, which leads to the duodenum  The acinar cells secrete digestive enzymes into the duct  The enzymes digest food in the duodenum

5. Pancreas-Endocrine Function  Endocrine-Glands that secrete hormones directly into the blood  The endocrine tissue in the pancreas are the islets of Langerhans  They are found in clusters around blood capillaries  The islets of Langerhans secrete hormones directly into the blood  They’re made up of two types of cell:  Alpha cells secrete glucagon  Beta cells secrete insulin

7. α and β cells in an Islet of Langerhans

8. Controlling the concentration of blood glucose As a meal is absorbed into the blood stream, the concentration of glucose may increase by 50%. These events occur when the blood glucose levels rise above the set point: 1.The increase in glucose acts as a stimulus that is detected by β cells in the islets of Langerhans, which release insulin in response. 2.Insulin circulates in the blood stream and binds to insulin receptors on target cells. 3.Insulin stimulates muscle and adipose cells to take up glucose and convert it into glycogen and fat. Insulin stimulates more channel proteins for glucose to move into the membranes of muscle and fat cells.

9. Controlling the concentration of blood glucose continued 4. Insulin has a number of effects on liver cells, including:  Increasing the use of glucose (eg in respiration)  Stimulating the conversion of glucose into glycogen-this is called glycogenesis  Inhibiting the breakdown of glycogen to glucose  Inhibiting the conversion of fats and proteins into glucose 5. Glucose is now being stored for later. It is converted into glycogen for short-term storage and converted to fat for long-term storage. The concentration of glucose in the blood decreases

10. Controlling the concentration of blood glucose After a meal has been absorbed completely and also during exercise, the blood glucose concentration may decrease below the set point. The following events then occur: 1.β-cells stop releasing insulin. Thus the cells take up less glucose 2.α-cells in the islets of Langerhans respond to decreasing concentrations of glucose by releasing glucagon 3.Glucagon circulates in the blood stream and binds to glucagon receptors on liver cells. The receptor interacts with adenyl cyclase to increase the concentration of cyclic AMP inside liver cells.

11. Glucagon stimulates liver cells to:  Activate the enzyme glycogen phosphorylase, which converts glycogen into glucose-this is called glycogenolysis  Convert fat and protein into intermediate metabolites that are then converted into glucose – this is called gluconeogenesis