Endocrine Tumors of the Pancreas

A Guide to Insulin, Glucagon, Somatostatin, and Gastrin

The human pancreas is an amazing organ with two main functions: [1] to produce pancreatic endocrine hormones (eg, insulin & glucagon), which help regulate many aspects of our metabolism and [2] to produce pancreatic digestive enzymes.  The hormone function of the pancreas is the emphasis of this portion of EndocrineWeb ~ this is referred to as the Endocrine Pancreas.  Pancreatic production of insulin, somatostatin, gastrin, and glucagon plays an important role in maintaining sugar and salt balance in our bodies, and therefore, any problem in the production or regulation of these hormones will manifest itself with problems with blood sugar and fluid / salt imbalances.

The digestive portion of the pancreas makes up more than 90% of its total cell mass.  The digestive (or exocrine) pancreas is responsible for making digestive enzymes which are secreted into the intestines to help digest (break down) the food we eat.  These enzymes digest proteins, fats, and carbohydrates into much smaller molecules so our intestines can absorb them.  The picture above is an accurate representation of the pancreas which lies next to the duodenum (the first part of the small intestine right after the stomach). The actual size of the pancreas is similar to a banana which has been stepped on...it has a slight curve to it, and its about the same length, width, and thickness.  The yellow "tube" running through the middle of the pancreas is called the pancreatic duct.  It drains all the digestive enzymes from the pancreatic cells where they are made into the duodenum where they mix with food as it comes out of the stomach. 

The Endocrine Pancreas

The emphasis of the remainder of these pages within EndocrineWeb is on the Endocrine Pancreas.  Approximately 5% of the total pancreatic mass is comprised of endocrine cells.  These endocrine cells are clustered in groups within the pancreas which look like little islands of cells when examined under a microscope.  This appearance led to these groups of pancreatic endocrine cells being called "Pancreatic Islets."  Within pancreatic islets are cells which make specific pancreatic endocrine hormones, of which there are only a few (the most famous, of course, being insulin).  These cells within the islets are called "Pancreatic Islet Cells."

Endocrine cells secreting hormones into blood vessels.Pancreatic islets are scattered throughout the pancreas.  Like all endocrine glands, they secrete their hormones into the bloodstream and not into tubes or ducts like the digestive pancreas.  Because of this need to secrete their hormones into the blood stream, pancreatic islets are surrounded by small blood vessels.  This relationship is shown in the picture of a pancreatic islet where islet cells are secreting their hormones into nearby blood vessels.  Remember, the purpose of endocrine cells is to make hormones which are secreted into the blood stream where they gain access to other cells very far away with the goal of making those cells respond in a specific fashion. 

Pancreatic Endocrine Hormones and Their Purpose

Insulin
Purpose:    Regulate blood glucose (sugar) in the normal range (lots more about this)
Action:    Forces many cells of the body to absorb and use glucose thereby decreasing blood sugar levels
Secreted in response to:     High blood glucose
Secretion inhibited by:     Low blood glucose
Disease due to deficient action:     Diabetes
Disease due to excess action:     Hypoglycemia
Tumor called:    Insulinoma

Glucagon
Purpose:    Assist insulin in regulating blood glucose (sugar) in the normal range (actions are opposite of insulin)
Action:    Forces many cells of the body to release (or produce) glucose (increasing blood sugar)
Secreted in response to:     Low blood glucose
Secretion inhibited by:     High blood glucose
Disease due to deficient action:     Some times nothing, sometimes hypoglycemia
Disease due to excess action:     Hyperglycemia
Tumor called:    Glucagonoma 

Somatostatin
Purpose:    Regulate the production and excretion of other endocrine hormones
Action:    Slows down production of insulin, glucagon, gastrin, and other endocrine hormones
Secreted in response to:     High levels of other endocrine hormones
Secretion inhibited by:     Low levels of other endocrine hormones
Disease due to deficient action:     Poorly defined
Disease due to excess action:     Diabetes, gallstones, and dietary fat intolerance
Tumor called:     Somatostatinoma

Gastrin
Purpose:    Assist in digestion within the stomach
Action:    Induce acid producing cells of the stomach to produce acid
Secreted in response to:     Food in the stomach and intestines
Secretion inhibited by:     Absence of food in stomach and intestines
Disease due to deficient action:     Poorly defined, some times no symptoms at all
Disease due to excess action:     Stomach ulcers due to excess stomach acid
Tumor called:    Gastrinoma (also called Zollinger Ellison Syndrome)

Vasoactive Intestinal Peptide (VIP)
Purpose:    Help control water secretion and absorption from the intestines
Action:    Causes intestinal cells to secrete water and salts into the intestines (inhibit absorption)
Secreted in response to:     Unclear
Secretion inhibited by:     Unclear
Disease due to deficient action:     No symptoms at all
Disease due to excess action:     Severe watery diarrhea and salt (potassium) imbalances
Tumor called:    VIPoma