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Pancreas
Chemical digestion in the small intestine relies on the activities of three
accessory digestive organs: the pancreas, liver and gall bladder. The
pancreas produces pancreatic juice, which contains digestive enzymes
and bicarbonate, and delivers it to the duodenum.
The digestive role of the liver is to produce bile and export it to the
duodenum. The gall bladder primarily stores and releases bile.
The soft, tadpole-shaped pancreas is a gland that is about 5-6 inches
(13-15 cm) long and 1 inch (2.5 cm) thick. It lies posterior to the greater
curvature of the stomach. The pancreas regions are described as the
head, body, and tail. The head is next to the duodenum. The body lies
behind the stomach. The tail is in contact with the spleen.
The pancreas and common bile duct. This work by Cenveo is licensed under a Creative Commons Attribution
3.0 United States (http://creativecommons.org/licenses/by/3.0/us/).
Pancreas Ducts
The
pancreas
is
important
in
digestion,
because
it
produces pancreatic juice, a combination of fluid and digestive
enzymes. Exocrine cells release this juice into small ducts that
eventually unite to create two larger ducts that deliver pancreatic juice
to the small intestine. The larger of these two ducts is the centrally
locatedmain pancreatic duct (duct of Wirsung). In most
individuals, this duct fuses with the common bile duct from the liver and
gall bladder before entering the duodenum via the hepatopancreatic
ampulla (ampulla of Vater), a dilated common duct. This ampulla
opens on the major duodenal papilla, an elevation of the duodenal
mucosa, which is situated approximately 4 inches (10 cm) inferior to the
pyloric sphincter of the stomach. The smooth muscle hepatopancreatic
sphincter controls the flow of pancreatic juice and bile into the small
intestine. The second large pancreatic duct, the accessory duct (duct
of Santorini) runs from the pancreas directly into the duodenum,
approximately 1 inch (2.5 cm) above the hepatopancreatic ampulla.
Pancreatic Islets
In the pancreas, small clusters of glandular epithelial (secretory) cells
surround the ducts. The exocrine structures of the pancreas contains 99
percent of the clusters that are called acini (singular - acinus). Cells of
the acini secrete pancreatic juice. The endocrine part of the pancreas is
made up of the remaining 1 percent of clusters, which are
called pancreatic islets (islets of Langerhans). These cells
produce the hormones pancreatic polypeptide, insulin, glucagon, and
somatostatin. Insulin and glucagon are important in carbohydrate
metabolism.
Panreatic Acini and Exocrine Digestive Function
Regulation of pancreatic secretion is the job of both hormones and the
parasympathetic nervous system. The hormone secretin, whose
secretion is stimulated by the presence of HCl in the intestine, provokes
cells of the pancreatic duct to release bicarbonate-rich pancreatic juice.
The presence of fats (and some proteins) in the intestine stimulates the
secretion of the hormone cholecystokinin (CCK), which then stimulates
the release enzyme-rich pancreatic juice and enhances the activity of
secretin. As a result, much more bicarbonate-rich juice is released in the
presence of both hormones. Parasympathetic regulation occurs mainly
during the cephalic and gastric phases of gastric secretion, when vagal
stimulation prompts the secretion of pancreatic juice.