Normal Pancreas

What is the pancreas?

The pancreas is a combination of TWO  glands, the exocrine pancreas and the endocrine pancreas.  The exocrine pancreas secretes substances into the intestine.  The endocrine pancreas secretes substances into the bloodstream.  The two glands work together during meals to digest the food (the exocrine pancreas) and to signal the rest of the body that nutrients are being digested and absorbed and on their way to other cells of the body (the endocrine pancreas).

The exocrine pancreas has two types of cells.

Acinus Duct model72The diagram illustrates the organization of the two major types of exocrine cells.  The acinar cells make powerful digestive enzymes (biological scissors) that can dissolve complex vegetables and meats, turning them into liquids.  The enzymes are made in an inactive form (zymogens) to keep the pancreas from digesting itself!

The duct cell makes fluid that mixes with the zymogens to make pancreatic juice.  The pancreatic juice flows from the acinar cells to the first part of the small intestine (duodenum).  The juice then mixes with the food as it leaves the stomach.  The juice has high concentrations of bicarbonate which neutralizes stomach acid.  Once in the intestine, the zymogens become active enzymes.

The endocrine pancreas has four types of cells.

The beta cell is the most important because it makes insulin.  As food is being digested within the intestine and the nutrients are being absorbed into the bloodstream, the beta cells also release insulin into the bloodstream.  Insulin is a signal for the cells of the body to stop using previously stored nutrients, and to start using new nutrients.

The endocrine pancreas has three additional types of cells that are not well known because they rarely cause disease.  They make glucagon, pancreatic polypeptide and somatostatin.

Normal Pancreas Histology

nl pancreas cellsThe photomicrograph shown here is of a normal pancreas.  Note that the majority of the pancreas is made of acinar cells.  The anatomy of the pancreas is also interesting because much of the blood coming to the pancreas goes to the islets first, then to the acinar cells, and then to the veins which take it to the liver on to the heart.

In the normal human pancreas, there are about 1,000,000 islets. Inflammation of the islets, thought to be an autoimmune problem triggered by a virus or some other factor, leads to Type 1 diabetes mellitus.  This happens as the beta cells (which make insulin) are destroyed.  The treatment is to replace the lost function of the endocrine pancreas by injecting insulin under the skin.  Type 2 diabetes mellitus is a disease linked to obesity in which the other cells of the body (including liver, muscle, fat and other tissues and organs) do not respond to insulin even though the pancreas is making plenty of it.

Where is the pancreas?

The pancreas is located in the back of the belly.  It is behind the stomach, with the diaphragm above it, the liver to the patient’s right, the spleen to the patient’s left, and intestines below it.  This location is one of the most protected sites of the body, making it resistant to injury, but hard to examine.

The image to the right is a 3D reconstruction of the pancreas (yellow) and supporting structures (red) made from a CT scan (Dr. Federle).  A=head of the pancreas, B=gastroduodenal artery, C=tail of the pancreas, D=aorta, E=superior mesentery artery, F=spine.

The pancreas develops by branching out of the upper intestine along with the liver.  the main duct of the pancreas joins the main duct of the liver (the common bile duct) and together, they empty their juices into the intestine to mix with food.

Can people live without a pancreas?

Yes.  In some cases the pancreas is destroyed by disease or must be removed because of cancer.  However, these patients must have the functions of the pancreas replaced or they will die.  Stomach acid must be suppressed to replace the function of the duct cell, pancreatic enzymes are required to digest food, and insulin must be injected to signal the cells of the body that the food is being digested and absorbed.