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Chapter: Medical Physiology: Physiology of Gastrointestinal Disorders

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Abnormal Digestion of Food in the Small Intestine-Pancreatic Failure

A serious cause of abnormal digestion is failure of the pancreas to secrete pancreatic juice into the small intestine.

Abnormal Digestion of Food in the Small Intestine-Pancreatic Failure

A serious cause of abnormal digestion is failure of the pancreas to secrete pancreatic juice into the small intestine. Lack of pancreatic secretion frequently occurs (1) in pancreatitis (which is discussed later), (2) when the pancreatic duct is blocked by a gallstone at the papillaof Vater, or (3) after the head of the pancreas has beenremoved because of malignancy.

Loss of pancreatic juice means loss of trypsin, chy-motrypsin, carboxypolypeptidase, pancreatic amylase, pancreatic lipase, and still a few other digestive enzymes. Without these enzymes, as much as 60 per cent of the fat entering the small intestine may be unab-sorbed, as well as one third to one half of the proteins and carbohydrates. As a result, large portions of the ingested food cannot be used for nutrition, and copious, fatty feces are excreted.

Pancreatitis. Pancreatitis means inflammation of thepancreas, and this can occur in the form of either acutepancreatitis or chronic pancreatitis.

The most common cause of pancreatitis is drinkingexcess alcohol, and the second most common cause is blockage of the papilla of Vater by a gallstone; the twotogether account for more than 90 per cent of all cases. When a gallstone blocks the papilla of Vater, this blocks the main secretory duct from the pancreas as well as the common bile duct. The pancreatic enzymes are then dammed up in the ducts and acini of the pancreas. Even-tually, so much trypsinogen accumulates that it over-comes the trypsin inhibitor in the secretions, and a smallquantity of trypsinogen becomes activated to form trypsin. Once this happens, the trypsin activates still more trypsinogen as well as chymotrypsinogen and car-boxypolypeptidase, resulting in a vicious circle until most of the proteolytic enzymes in the pancreatic ducts and acini become activated. These enzymes rapidly digest large portions of the pancreas itself, sometimes completely and permanently destroying the ability of the pancreas to secrete digestive enzymes.


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