pancreas

views updated May 29 2018

pancreas The pancreas (from the Greek meaning ‘all flesh’) is a pale, rubbery gland in the upper part of the abdomen, responsible for the production of digestive juices and hormones. The juices pass into the cavity of the duodenum (an example of exocrine secretion) while the hormones pass into the circulating blood (endocrine secretion). By means of these products the pancreas is essential to the proper processing of food, through digestion to absorption, storage, and utilization of nutrients.

Early authors found great difficulty in ascribing a function to the organ, as its rather evasive name implies. The rubbery texture suggested to some that the gland might be a shock absorber preventing the stomach from damaging itself on the vertebral column. It was not until the nineteenth century that any firm ideas of its function evolved. It was known that a small tube (the ‘duct of Wirsung’, described by him in 1642) connected the gland with the duodenum; in 1664, de Graaf inserted a wild duck's quill into the duct of a dog and collected a clear fluid, which he examined and decided was acidic. He had no idea of the fluid's function — and we now know that pancreatic juice is unambiguously alkaline, because the cells lining the duct system secrete bicarbonate ions.

Exocrine function

The function of the digestive juices became known long before hormones were recognized. The advances in chemistry in the nineteenth century led the way to understanding the process of digestion. It became clear that pancreatic juice contained agents — ‘ferments’ (subsequently renamed enzymes) that were capable of breaking down the three major components of food: carbohydrates, fats, and proteins. Many of the molecules in our diet are large, having been synthesized by the plant or animal being eaten. These large molecules are then reduced in size by the enzymes from the pancreas — continuing the digestive process already begun in the stomach; only small molecules can be absorbed from the intestines. Carbohydrates are broken down to simple sugars (mono- and di-saccharides) by pancreatic amylase, fats to glycerol and fatty acids by pancreatic lipase, and proteins to amino-acids and small peptides by a variety of proteolytic enzymes. The French physiologist Claude Bernard showed in the 1840s that both pancreatic juice and bile (from the liver) were necessary for the absorption of fat. These two fluids enter the duodenum together where their main ducts converge. We know now that bile, by a detergent action, converts fats into tiny particles (micelles), and it is only when the surface area of the fat has been increased in this way that the lipase in pancreatic juice can break the fats down to fatty acids and glycerol. Probably to prevent the pancreas from digesting itself, proteolytic enzymes are secreted by the gland as ‘pro-enzymes’. These molecules are inactive at digesting protein until they reach the cavity of the duodenum, where they are rendered active by another enzyme (enterokinase). Chronic disease of the exocrine component of the pancreas often results in a deficiency of pancreatic enzymes, giving rise to poor absorption of foodstuffs: the excretion of fat in faeces (steatorrhoea) provides the most conspicuous feature of this malabsorption. Microscopically, the gland is divided up into units known as acini (acinus: Latin for ‘berry’). Each acinus is spherical, with the enzyme-secreting cells surrounding a central space (remarkably, every enzyme-secreting cell synthesizes all the pancreatic enzymes). The enzymes pass into the centre of the acini, whence they enter the narrowest ducts of the branching secretory system, and then pass by larger and larger ducts to the single pancreatic duct itself. The cells lining the duct system secrete water and bicarbonate ions and add them to the enzymes; the final juice is consequently alkaline.

The volume of juice secreted precisely neutralizes the acid contents of the stomach as they both enter the duodenum. This remarkable feat of homeostasis is brought about by acid in the duodenum causing release of the hormone secretin from cells in its wall; this secretin passes into the bloodstream and stimulates the production of water and bicarbonate ions from the duct system of the pancreas. Hence the greater the volume of acid gastric juice passing into the duodenum, the greater the volume of bicarbonate-rich juice produced by the pancreas. This tends to keep the contents of the duodenum neutral — the pH at which the pancreatic enzymes are most effective. Secretin, a protein hormone, was first demonstrated by Bayliss and Starling in London in 1902 — the earliest recognition that such ‘chemical messengers’ existed.

A similar mechanism exists for the enzyme component of pancreatic juice. Another hormone, cholecystokinin (literally ‘gall-bladder mover’) is synthesized in the wall of the duodenum and jejunum, and is released in response to the presence of amino acids and fatty acids as partly-digested food starts to arrive from the stomach. Cholecystokinin passes round the circulation and causes enzyme secretion by the pancreatic acinar cells, thereby increasing the ability of the juice to break down more fats and proteins. Cholecystokinin also causes contraction of the gall bladder, providing bile that promotes the absorption of fatty acids and glycerol. About a litre of pancreatic juice is secreted each day in a person with typical eating habits.

Endocrine function

The main ‘internal’ secretions of the pancreas are the hormones insulin and glucagon. These are necessary for the regulation of storage, release, and utilization of fuels for metabolism. Insulin has a well-known association with sugar (glucose) in the body, because of its role in diabetes. Insulin lowers the blood sugar, and glucagon raises it; but these hormones are also important in the body's handling of nutrients derived from fat and protein, as well as carbohydrate.

Among the acini and ducts which secrete enzymes and bicarbonate there are small clumps of cells which do not connect with a duct system. These account for a small fraction of the bulk of the pancreas, but their function is vital. They were first described by Langerhans, in his MD thesis in 1869. A clue to their function came twenty years later, when Mering and Minkowski, in Strasbourg, removed the pancreas from dogs under surgical anaesthesia, and found that they developed the features of human diabetes. At the turn of the century, Opie, at Johns Hopkins University, reported degeneration of the ‘islands of Langerhans’ in the pancreas of people who had died from diabetes. In 1916, the English physiologist Sharpey-Schafer linked these observations and proposed that diabetes was due to the lack of an internal secretion — a hormone — from the ‘islets’. All this provided the background and the impetus for the accelerating and better known part of the story: the preparation in 1921 by Banting and Best, in Macleod's laboratory in Toronto, of an extract of pancreatic tissue, which reversed the rise in blood sugar in dogs whose pancreas had been removed. Next, the biochemist Collip prepared a refined extract, which was first used to treat human diabetes mellitus in 1922. Thus it was proved that the pancreas had an internal secretion — and it was named insulin from Latin insula; an island. The ‘islets’ were later shown to have two main types of endocrine cell, one producing insulin (beta cells) and the other producing glucagon (alpha cells). In the liver, the two hormones influence in opposite directions the balance between the storage of glucose (as glycogen) and its release into the blood; and they have contrary effects on new formation of glucose from amino acids. In fatty tissue they likewise have opposing effects on storage versus release of fuels. Insulin facilitates the uptake and usage of glucose by body tissues, notably muscle. In these ways the two hormones have opposite effects on the level of glucose in the blood.

The insulin: glucagon (I:G) ratio is therefore important and variable. By this balance, blood glucose level in particular is maintained for supplying the brain, nutrient supply in general is matched to the immediate needs of the body's tissues, and surplus is stored. When nutrients flood into the blood after digestion of a meal, insulin takes precedence, facilitating uptake and storage: the I:G ratio is high. When use of fuels for energy is at a peak during muscular work, glucagon promotes release of glucose and of fatty acids into the circulating blood, from liver and adipose stores: the I:G ratio is relatively low. In fasting, and its extension to starvation, glucagon is of major importance, along with others of the body's hormones.

The regulation of these counterbalancing secretions is mainly by direct response of the secretory cells to the levels of glucose and amino acids in the blood supplying the pancreas: for example, a rise in blood glucose affects cell membrane receptors on beta cells, resulting in enhancement of synthesis and extrusion of insulin.

In recent years it has become clear that the islets secrete several more hormones (apart from insulin and glucagon). These include gastrin and pancreatic polypeptide. How these interact with insulin and glucagon is the subject of much current research.

Autonomic effects

As well as the hormonal and chemical mechanisms for regulating the exocrine and endocrine functions of the pancreas, the autonomic nervous system plays a faster, and even anticipatory role — preparing the pancreas to deal with food which is on its way. Parasympathetic fibres from the vagus nerves stimulate enzyme secretion in response to eating, before ever the meal reaches the duodenum, and branches from the network of autonomic nerves in the nearby gut send signals related to events in the stomach and duodenum. The hormone-secreting cells also are supplied by nerves from both the sympathetic and the parasympathetic systems, which respectively inhibit and promote insulin release, and have the reverse action on glucagon. These actions accord with nutrient mobilization from body stores during exercise and stress, and on the other hand, the need for storage after digestion of a meal.

The pancreas is thus vital for the proper ‘feeding’ of the body tissues. Without its exocrine function, the digestion and absorption of foodstuffs is deranged. Without its endocrine function, untreated, we cannot long survive the inability to organize the use or storage of nutrients after their intake to the bloodstream.

John Henderson, and Sheila Jennett


See also alimentary system; blood sugar; insulin.

Pancreas

views updated May 23 2018

Pancreas

Definition

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.

Function

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.

Similarly, the body cannot maintain normal blood sugar levels without the balanced action of insulin and glucagon. Both hypoglycemia (low blood sugar) and hyperglycemia (high blood sugar) cause symptoms and serious health problems.

Common diseases and disorders

Diabetes

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.

Resources

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.

OTHER

National Institutes of Health. <http://www.niddk.nih.gov>.

Pancreas Foundation. <http://www.pancreasfoundation.org>.

Erika J. Norris

Pancreas

views updated May 17 2018

Pancreas

Definition

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 and 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.

Function

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.

Similarly, the body cannot maintain normal blood sugar levels without the balanced action of insulin and glucagon. Both hypoglycemia (low blood sugar) and hyperglycemia (high blood sugar) cause symptoms and serious health problems.

Common diseases and disorders

Diabetes

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 1 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 1 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 2 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 2 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 2 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.

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.

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.

Resources

BOOKS

"Gastrointestinal Disorders." in The Merck Manual of Diagnosis and Therapy, edited by Mark H. Beers, MD, and Robert Berkow, MD. Whitehouse Station, NJ: Merck Research Laboratories, 2005.

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.

OTHER

National Institutes of Health. 〈http://www.niddk.nih.gov〉.

Pancreas Foundation. 〈http://www.pancreasfoundation.org〉.

Pancreas

views updated Jun 11 2018

Pancreas

The pancreas is a soft oblong organ located in the upper central region of the abdominal cavity, just behind the lower surface of the stomach. It has three portions: an expanded medial portion called the head, a central portion called the body, and a tapering lateral portion called the tail. The head is partially encircled by the C-shaped duodenum, the first portion of the small intestine. The pancreas is both an exocrine gland and an endocrine gland.

The exocrine portion of the pancreas consists of acinar cells (which account for about 99 percent of all secretory cells in the pancreas) that are organized into numerous small clusters called acini. The acinar cells secrete a clear fluid called pancreatic juice, which plays a critically important role in the digestion of food within the small intestine. The pancreatic juice is usually delivered to the duodenum by way of two ducts, the main pancreatic duct and the accessory pancreatic duct. (In some people, the accessory duct disappears during development.) Pancreatic juice consists of water, electrolytes , sodium bicarbonate, and several digestive enzymes capable of digesting virtually all the nutrient molecules in food.

Among these enzymes are several protein -digesting enzymes (trypsin, chymotrypsin, carboxypeptidase, and elastase), a carbohydrate-digesting enzyme (pancreatic amylase), and a lipid -digesting enzyme (pancreatic lipase). These enzymes do not digest the pancreas itself because they are not activated or provided with optimal ionic conditions until pancreatic juice enters the duodenum. The sodium bicarbonate establishes the optimal pH for the actions of pancreatic and intestinal enzymes within the small intestine.

The remaining 1 percent of the secretory cells form the endocrine portion of the pancreas. These cells are organized into clusters called pancreatic islets (islets of Langerhans) that are scattered among the acini. These cells secrete several hormones , including glucagon (secreted by alpha cells) and insulin (secreted by beta cells), which play important roles in blood glucose regulation and carbohydrate metabolism . Diabetes mellitus is an endocrine disorder that arises from hyposecretion of insulin or a decreased sensitivity of body cells to insulin.

see also Blood Sugar Regulation; Digestive System; Endocrine System; Enzymes; Hormones

Izak Paul

Bibliography

Saladin, Kenneth S. Anatomy & Physiology: The Unity of Form and Function, 2nd ed. New York: McGraw-Hill, 2001.

pancreas

views updated Jun 11 2018

pancreas A gland in vertebrates lying between the duodenum and the spleen. Under the influence of the hormone secretin it secretes pancreatic juice containing digestive enzymes or their precursors (mainly trypsin, chymotrypsin, amylase, and lipase) into the duodenum via the pancreatic duct (see acinus). It also contains groups of cells – the islets of Langerhans – that function as an endocrine gland, producing the hormones insulin and glucagon, which regulate blood sugar levels.

pancreas

views updated May 18 2018

pancreas Elongated gland lying behind the stomach, to the left of the mid-line. It secretes pancreatic juice into the small intestine to aid digestion. Pancreatic juice contains the enzymes amylase, trypsin, and lipase. The pancreas also contains a group of cells known as the islets of Langerhans, which secrete the hormones insulin and glucagon, concerned with the regulation of blood-sugar level. See also diabetes

pancreas

views updated May 14 2018

pan·cre·as / ˈpangkrēəs; ˈpankrēəs/ • n. (pl. -cre·as·es) a large gland behind the stomach that secretes digestive enzymes into the duodenum. Embedded in the pancreas are the islets of Langerhans, which secrete into the blood the hormones insulin and glucagon.DERIVATIVES: pan·cre·at·ic / -krēˈatik/ adj.

pancreas

views updated May 14 2018

pancreas (pank-ri-ăs) n. a compound gland, about 15 cm long, that lies behind the stomach. One end lies in the curve of the duodenum; the other end touches the spleen. It is composed of clusters (acini) of cells that secrete pancreatic juice into the duodenum via the pancreatic duct, which unites with the common bile duct. Interspersed among the acini are the islets of Langerhans, which secrete the hormones insulin and glucagon into the bloodstream.
pancreatic (pank-ri-at-ik) adj.

pancreas

views updated May 21 2018

pancreas A gland in the abdomen with two functions: the endocrine pancreas (the islets of Langerhans) secretes the hormones insulin and glucagon; the exocrine pancreas secretes the pancreatic juice. Known by the butcher as sweetbread or gut sweetbread, as distinct from chest sweetbread which is thymus.

pancreas

views updated May 29 2018

pancreas In vertebrates, a gland lying between the duodenum and spleen, that secretes trypsin and other digestive enzymes, and that contains the islets of Langerhans.