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
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
Secretion of hormones (endocrine function) Hormones are secreted from the cells in the islets of Langerhans α cells manufacture and secrete the hormone glucagon β cells manufacture and secrete the hormone insulin These are released directly into the blood
Control of blood glucose The natural sources of blood glucose are: 1.Directly from the diet – glucose enters blood when carbohydrates are broken down 2.Breakdown of glycogen ( Glycogenolysis ) 3.Gluconeogenesis – production of new glucose from sources other than carbohydrates
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.
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
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.
The result… Increased rate of conversion of glucose to glycogen ( glycogenesis ) in the liver and muscles.
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 LIVER cells only.
When bound the following happens: a)An enzyme is activated that converts glycogen to glucose (GLYCOGENOLYSIS). b)There is an increase in the conversion of amino acids and glycerol into glucose (GLUCONEOGENESIS). This results in an increase in blood glucose levels.
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.
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
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
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.
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.