The pancreas is an organ important in digestion and blood sugar regulation. It is considered to be part of the gastrointestinal system. The pancreas produces digestive enzymes to be released into the small intestine to aid in reducing food particles to basic elements that can be absorbed by the intestine and used by the body. It has another very different function in that it forms insulin, glucagon and other hormones to be sent into the bloodstream to regulate blood sugar levels and other activities throughout the body.
Description
The pancreas is a pear-shaped organ about 6 in (15 cm) long located in the middle and back portion of the abdomen. It is connected to the first part of the small intestine, the duodenum, and lies behind the stomach. The pancreas is made up of glandular tissue, or cells that form substances to be secreted outside of the organ. Glandular tissues can be categorized as endocrine (secreting directly into the bloodstream or lymph) or exocrine (secreting into another organ). The pancreas is both an exocrine and an endocrine organ.
Exocrine secretions
The digestive juices produced by the pancreas are secreted into the duodenum via a Y-shaped duct, at the point where the common bile duct from the liver and the pancreatic duct join just before entering the duodenum. In this way, a variety of digestive enzymes (trypsin, chymotrypsin, lipase, and amylase, among others) are delivered into the small intestine to aid in the digestion of proteins, fats, and carbohydrates. The enzymes are delivered in an inactive form called zymogens. The zymogens are activated by the chemical substances in the small intestine. The digestive enzymes carried into the duodenum are representative of the exocrine function of the pancreas, in which specific substances are made to be passed directly into another organ.
Endocrine secretions
The pancreas is unusual among the body's glands in that it also has a very important endocrine function. Small groups of special cells called islet cells throughout the organ make such hormones as insulin and glucagon, which are critical in regulating blood sugar levels; and vasoactive intestinal peptide, which influences gastrointestinal activity. These hormones are secreted directly into the bloodstream to affect organs all over the body. No organ except the pancreas makes significant amounts of insulin or glucagon, but other tissues do produce vasoactive intestinal peptide. Insulin acts to lower blood sugar levels by allowing the sugar to flow into cells. Glucagon acts to raise blood sugar levels by causing glucose to be released into the circulation from its storage sites. Insulin and glucagon act in an opposite but balanced fashion to keep blood sugar levels stable.
Role in human health
A normal pancreas is important for maintaining good health, preventing malnutrition, and maintaining normal levels of blood sugar. The digestive tract needs the help of the enzymes produced by the pancreas to reduce food particles to their simplest elements, or the nutrients cannot be absorbed. Carbohydrates must be broken down into individual sugar molecules. Proteins must be reduced to simple amino acids. Fats must be broken down into fatty acids. The pancreatic enzymes are important in all these transformations. The basic particles can then easily be transported into the cells that line the intestine, and from there they can be further altered and transported to different tissues in the body as fuel sources and construction materials.
Glucose is a simple sugar molecule, but one that is necessary to every type of cell as a major source of energy. Insulin made in the pancreas has a critical role in permitting glucose to enter cells. Without insulin, the cells of the body literally "starve in the midst of plenty," and are unable to make use of sugar in the blood even if blood sugar levels are very high. This condition is called diabetes mellitus. Diabetes actually represents a collection of disorders resulting in high blood sugars related to abnormal insulin levels, or abnormalities of the receptor that binds the insulin to allow glucose to enter the cell. Diabetes is quite common in the United States, affecting 1–2% of the general population.
Type I diabetes, which is sometimes called insulin-dependent diabetes, is a disease in which a patient must use insulin regularly to avoid serious problems with cells starving for glucose and acidic waste products accumulating in the blood. In this form of diabetes, the pancreas is essentially not producing insulin. Pancreas transplantation is a method of treating type I diabetes that has achieved success rates of 80–85% in the past decade, success being defined as the organ recipient's remaining insulin-independent. In type II diabetes, or non-insulin-dependent diabetes, blood sugar levels can often be controlled with diet, exercise, and medications taken by mouth. In some forms of type II diabetes the pancreas is not producing enough insulin; in other cases the receptor that binds insulin is no longer sensitive to it, or too few receptors are made by the cells that need glucose. Sometimes a combination of these problems is present. Gestational diabetes mellitus (GDM) is a third type of diabetes, which is a temporary problem with blood sugar levels that exists only during pregnancy. Women with GDM, however, need to know they are at increased risk for developing type II diabetes.
Pancreatitis
Pancreatitis is a relatively common condition that affects the pancreas. It can occur as an acute (sudden onset) problem or chronic (slow, ongoing) disorder. The common element in both types is inflammation caused by the normal digestive enzymes of the pancreas. In pancreatitis, these secretions act abnormally and start to digest the pancreas itself. Between 50,000 and 80,000 people in the United States develop acute pancreatitis every year, usually related to gallstones or alcohol abuse. Most patients recover within a week, but the most severe forms of pancreatitis have a mortality rate of 10%. Chronic pancreatitis is slow and insidious in onset, and
so harder to diagnose. Alcohol use is the most common cause of deterioration in pancreatic function over time. Without adequate levels of enzymes and hormones produced by the pancreas, such diseases as diabetes mellitus and malabsorption syndromes will develop. A malabsorption syndrome is a condition in which the body is not able to absorb the nutrients it needs from the food it attempts to digest. Vitamin deficiencies, protein malnutrition, and problems with frequent, greasy stools may occur.
Complications of pancreatitis include pancreatic necrosis (the death of a significant portion of the cells in the pancreas, putting the patient at risk of bleeding, infection, shock, and failure of many major organs); pancreatic abscess (an infection with a wall of scar tissue around it); and pancreatic pseudocyst (a pocket full of fluid and pancreatic enzymes that may shrink, expand, or rupture). Patients with chronic pancreatitis are also at increased risk of developing cancer of the pancreas.
KEY TERMS
Amino acids—The category of molecules used to build proteins.
Diabetes mellitus—A chronic form of diabetes in which insulin does not effectively transport glucose from the bloodstream.
Duodenum—The portion of the small intestine that lies between the stomach and the jejunum. The pancreas empties some of its secretions into the duodenum via a Y-shaped duct.
Endocrine—A type of gland that secretes hormones directly into the blood or lymph.
Enzymes—Complex protein molecules that speed up chemical reactions, or make reactions happen under conditions where they normally would not occur.
Exocrine—A type of gland that secretes its products to an epithelial surface.
Glucagon—A hormone secreted by the pancreas that opposes insulin in the regulation of blood sugar levels.
Insulin—A hormone produced in the islet cells of the pancreas that regulates the metabolism of glucose and other nutrients.
Islet cells—Endocrine cells in the pancreas that are specialized to secrete glucagon or insulin.
Jaundice—A condition in which the skin and whites of the eyes are yellow because of bile products retained in the bloodstream.
Pancreatitis—Inflammation of the pancreas.
Zymogens—Enzyme precursor molecules that may change into enzymes as a result of catalytic change.
Cancer of the pancreas
Pancreatic cancer is a major cause of death from cancer around the world. Tumors of the pancreas may arise from either endocrine or exocrine cells. Some rare types of pancreatic tumors hypersecrete either glucagon (glucagonomas) or insulin (insulinomas). Cancer of the pancreas is difficult to diagnose in its early stages; about 90% of patients present with pain, diarrhea, blood clots, weight loss, or jaundice when the cancer has already spread outside the pancreas. As of 2001, about 25,000 people die every year with this disease, and there are few medical interventions to help these patients. Under certain circumstances, chemotherapy or surgery to remove part of the pancreas may be attempted. Only 2–5% of patients are alive five years after being diagnosed.
BOOKS
"Gastrointestinal Disorders." Section 3 in The Merck Manual of Diagnosis and Therapy, edited by Mark H. Beers, MD, and Robert Berkow, MD. Whitehouse Station, NJ: Merck Research Laboratories, 1999.
Izenberg, Neil, et al. Human Disease and Conditions. New York: Charles Scribner's Sons, 2000.
Tierney, Laurence M., Stephen J. McPhee, and Maxine A. Papadakis. Current Medical Diagnosis and Treatment 2001. New York: McGraw-Hill, 2001.
ORGANIZATIONS
American Diabetes Association. 1660 Duke Street, Alexandria, VA 22314. (800) 232-3472.
National Digestive Diseases Information Clearinghouse. 2 Information Way, Bethesda, MD 20892. (301) 654-3810 or (800) 891-5389.
