The pancreas is an oblong flattened (fish-shaped) spongy gland, which has two main functions, exocrine and endocrine.
The pancreas is an oblong flattened (fish-shaped) spongy gland, which is grayish-pink in color and about six inches (15 cm) long. It’s deep in the abdomen and stretches across the back of it, behind the stomach, sandwiched between the stomach and the spine. The head of the pancreas is on the right side of the abdomen. It’s connected to the duodenum or the first section of the small intestine. The narrow end of the gland, which is called the tail, extends to the left side of the body. The part that isn’t behind the stomach is nestled in the curve of the small intestine.
Because the pancreas is so deep in the abdomen, tumors are rarely palpable. The tumors are usually not found until symptoms appear when the tumor grows large enough to interfere with the function of the stomach, duodenum, liver or gallbladder . These are the organs, which are near the pancreas.
The pancreas has two main functions and is; therefore, a compound gland. It has exocrine tissue and endocrine tissue. The exocrine function of the pancreas is to synthesize and secrete pancreatic juice and enzymes. The pancreatic juice is an alkaline fluid. The enzymes help digest food in the small intestine. These enzymes and juice flow into the main pancreatic duct. This duct joins the common bile duct, which connects the pancreas to the liver and the gall bladder . The common bile duct connects to the small intestine near the stomach and carries bile, which is a fluid that helps to digest fat. The digestive enzymes that pass to the small intestine help to further breakdown protein, carbohydrates, and fat in chyme. The acinar cells of the exocrine pancreas produce and secrete the enzymes, which include trypsin, chymotrypsin, pancreatic lipase, and pancreatic amylase. The enzymes are secreted into the small intestines in response to the hormones, secretin and cholecystokinin. Specific cells that line the pancreatic ducts, which are called centroacinar cells, secrete a bicarbonate and salt rich solution into the small intestine.
The exocrine pancreas is regulated by both neural and endocrine controls. In between periods of digestion, very little secretion takes place. As food enters the stomach and then a little later, chyme flows into the small intestine, pancreatic secretion is strongly stimulated. The pancreas is innervated by the vagus nerve, which applies low level stimulus to cause secretion, in response to the anticipation of a meal. But the most important stimuli for pancreatic secretion come from three hormones, which are secreted by the enteric endocrine system; these three hormones being, cholecystokinin, secretin and gastrin.
Cholecystokinin is synthesized and secreted by enteric endocrine cells that are located in the duodenum. The presence of partially digested proteins and fats in the small intestine is a strong stimulus to its secretion. As chyme flows into the small intestine, cholecystokinin is released into the blood and binds to receptors on the pancreatic acinar cells, which causes them to secrete large quantities of digestive enzymes.
Secretin is produced by endocrinocytes, which are located in the epithelium of the proximal small intestine. It’s secreted in response to acid in the duodenum when acid-laden chyme flows through the pylorus from the stomach. The main effect of secretin on the pancreas is to stimulate duct cells to secrete water and bicarbonate. As soon as this takes place, the enzymes secreted by the acinar cells are flushed out of the pancreas, through the pancreatic duct into the duodenum.
Gastrin is a hormone very similar to cholecystokinin. It’s secreted in large amounts by the stomach in response to gastric irritation and distention. In addition to stimulating acid secretion by the parietal cells, the hormone gastrin stimulates acinar cells to secrete digestive enzymes
Pancreatic secretions are the major mechanism for neutralizing gastric acid in the small intestine. When acid enters the small intestine, secretin is released and this in turn stimulates secretion of bicarbonate. As protein and fats are digested and absorbed the acid is neutralized and the stimuli for cholecystokinin and secretin secretion disappear and pancreatic secretion diminishes.
The endocrine part of the pancreas is made up of approximately one million cell clusters called islets of Langerhans. Four main cell types exist there. Their secretion classifies them. Alpha cells secrete glucagon that opposes the action of insulin. Beta cells secrete insulin, which helps to control carbohydrate metabolism and controls the amount of sugar in the blood. Delta cells secrete somatostatin and PP cells secrete pancreatic polypeptide. The pancreatic production of the hormones, insulin, glucagon, somatostatin and gastrin plays a very important role in maintaining sugar and salt balance in our bodies. Any problem in the production or regulation of the hormones will manifest itself as problems with blood sugar and fluid and salt imbalances.
Pancreatic Endocrine Hormones and Their Purpose
|Insulin||Regulate blood glucose (sugar) in the normal range||Forces many cells of the body to absorb and use glucose thereby decreasing blood sugar levels|
|Glucagon||Assist insulin in regulating blood glucose (sugar) in the normal range (actions are opposite of insulin)||Forces many cells of the body to release (or produce) glucose (increasing blood sugar)|
|Somatostatin||Regulate the production and excretion of other endocrine hormones||Slows down production of insulin, glucagon, gastrin, and other endocrine hormones|
|Gastrin||Assist in digestion within the stomach||Induce acid producing cells of the stomach to produce acid|
|Vasoactive Intestinal Peptide (VIP)||Help control water secretion and absorption from the intestines||Causes intestinal cells to secrete water and salts into the intestines (inhibit absorption)|