Pancreas and insulin

how your pancreas produces insulin

Your pancreas is one of the organs of your digestive system. It lies in your abdomen, behind your stomach. It is a long thin structure with 2 main functions:

  • producing digestive enzymes to break down food; and
  • producing the hormones insulin and glucagon to control sugar levels in your body.

Production of digestive enzymes

The pancreas produces secretions necessary for you to digest food. The enzymes in these secretions allow your body to digest protein, fat and starch from your food. The enzymes are produced in the acinar cells which make up most of the pancreas. From the acinar cells the enzymes flow down various channels into the pancreatic duct and then out into the duodenum. The secretions are alkaline to balance the acidic juices and partially digested food coming into the duodenum from the stomach.

Production of hormones to control blood sugar levels

A small proportion (1-2 per cent) of the pancreas is made up of other types of cells called islets of Langerhans. These cells sit in tiny groups, like small islands, scattered throughout the tissue of the pancreas. The islets of Langerhans contain alpha cells which secrete glucagon and beta cells which secrete insulin.

Insulin and glucagon are hormones that work to regulate the level of sugar (glucose) in the body to keep it within a healthy range. Unlike the acinar cells, the islets of Langerhans do not have ducts and secrete insulin and glucagon directly into the bloodstream.

Depending on what you’ve eaten, how much exercise your muscles are doing, and how active your body cells are, the amount of glucose in your bloodstream and cells varies. These 2 hormones have the job of keeping tight control of the amount of glucose in your blood so that it doesn’t rise or fall outside of healthy limits.

How insulin works

Insulin is released from the beta cells in your pancreas in response to rising glucose in your bloodstream. After you eat a meal, any carbohydrates you’ve eaten are broken down into glucose and passed into the bloodstream. The pancreas detects this rise in blood glucose and starts to secrete insulin.

Insulin works by improving the uptake of glucose from the blood across cell membranes and into the cells of the body, and so takes glucose out of the bloodstream. Once in the cells, the glucose is used as the energy to fuel the cells doing their different jobs or is stored in the liver or muscle cells as glycogen. This results in the glucose level of the blood dropping, which then triggers the pancreas to switch off the release of insulin.

The problem in people with diabetes is that either they don’t produce enough insulin, or the insulin they do produce doesn’t work properly, or their cells don’t respond properly to insulin. The net result is that glucose isn’t cleared from their bloodstream and they have high blood glucose levels which the body tries to clear by various compensatory methods, such as increased urination.

How glucagon works

Glucagon has an opposite (antagonistic) effect to insulin. When your blood glucose level falls, for example during exercise when your muscles are using glucose for fuel, your pancreas detects the drop in blood glucose. This prompts the pancreas to slow down the secretion of insulin, but increase the output of glucagon.

The role of glucagon is to break down glycogen (the stored form of glucose) in the liver. Then the liver releases glucose into the bloodstream. This results in a rise in the blood glucose level to bring it back to a healthy level, which in turn signals the pancreas to switch off glucagon release.

The control of blood glucose levels operates by what is known as a negative feedback mechanism. Here is a summary of the 2 control loops.

When the blood glucose level goes up

  • Blood sugar (glucose) rises;
  • The pancreas detects the rise;
  • The pancreas pumps out insulin into the blood;
  • Insulin helps the uptake of glucose into muscles and other cells;
  • This causes the blood glucose level to fall to its normal set point; and
  • The pancreas detects the fall and switches off insulin production.

When the blood glucose level goes down

  • Blood sugar (glucose) drops;
  • The pancreas detects the drop in blood sugar;
  • The pancreas switches on the output of glucagon into the blood;
  • Glucagon signals the liver to break down glycogen into glucose;
  • The liver releases glucose into the bloodstream;
  • Blood glucose goes up to its normal set point; and
  • The pancreas detects the rise in blood sugar and switches off glucagon release.

 
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