Question

The pancreas plays a key role in digestion and in controlling the body's fuel metabolism. Therefore, changes in either the exocrine or the endocrine functions of the pancreas seriously impact homeostasis. Mr. G.I. is an alcoholic with a long history of chronic pancreatitis. X-rays taken during his most recent hospitalization showed extensive calcified fibrous tissue throughout the pancreas. 1. The exocrine pancreas is made up of two structures, each of which contributes to the production of pancreatic juice. List the two structural components and their secretory products. 2. Predict the consequences (increase, decrease, no change) of the loss of one of these components on digestion and absorption of the following: carbohydrates, proteins, fats. Explain each prediction. 3. Predict the consequences (increase, decrease, no change) of the loss of the second pancreatic exocrine component on the digestion and absorption of these same three categories of chemicals. Explain each prediction. The diagnosis of chronic pancreatitis is often made by delivering physiological stimuli to the pancreas by intravenous administration of some agent and then measuring the response using a catheter placed in the duodenum to collect samples of pancreatic juice. 4. What agent would you use to stimulate enzyme secretion? Explain. 5. What agent would you use to stimulate fluid secretion? Explain. The pancreas also exhibits important endocrine functions. Pancreatitis can also affect these functions. 6. How might Mr. G.I.'s general metabolism be altered by a loss of pancreatic endocrine function?

Answer 1

1. Pancreas produces various digestive enzymes(proteases like trypsin, chymotrypsin; amylase, lipase). The enzymes are released in the inactive zymogenic form. The enzymes are produced by acinar cells. The other component of pancreatic juice is the bicarbonate (HCO₃^-) secreted by duct cells of pancreas.

2. If the digestive enzymes are not produced, there will be decrease in the digestion of carbohydrates. This is because of the fact that pancreatic amylase will not be there to carry out thedigestion of carbohydrates. Simiarly, if the pancreatic proteases like trypsin and chymotrypsin are not secreted, there will be much decreae in the digestion of proteins. Also, if there is no pancreartic lipase, the digestion would be affected (decrease in digestion of lipids). If the digestion is incomplete, the amount of nutrients absorbed will also be very less. (As undigested material will not be absorbed by our body).

3. If bicarbonate is not there in the pancreatic juice, it will also result into decrease in the digestion of carbohydrates, lipids and proteins. This is because of the fact that bicarbonate helps to neutralize the acidic pH of the chyme enterining into the small intestine. The bicarbonate helps in maintaining the alkaline pH in small intestine. At, this alkaline pH, the pancreatic enzymes are able to function properly. At lower pH, these will not be able to carry on digestion properly. Hence, the digestion and absorption will be lesser.

4. For stimulation of enzyme secretion, cholecystokinin (CCK) is used. During digestion, when the chyme from stomach reaches the duodenum, the fats and peptides present in the chyme stimulate the endocrine cells of duodenal epithelium secrete CCK. CCK then reaches to the pancreas via the circulatory system and induces the acinar cells of pancreas to secrete digestive enzymes. During the test we introduce CCK from outside into the patient's body and assess the production of pancreatic digestive enzymes.

5. For stimulation of fluid (bicarbonate) secretion, secretin is used. During digestion, when the chyme from stomach reaches the duodenum, the H+ ions present in the chyme (low pH) stimulate the endocrine cells of duodenal epithelium secrete secretin. Secretin then reaches to the pancreas via the circulatory system and induces the duct cells of pancreas to secrete bicarbonate (fluid) . During the test we introduce secretin from outside into the patient's body and assess the production of pacreatic fluid (containing bicarbonate).

6. Pancreatic beta cells are responsible for secretion of insulin. This hormone prevents excessive increase in the blood glucose level. If these hormone is not produced by the body the patient may develop diabetes. Another important hormone produced by pancreas is the glucagon (produced by alpha cells). It helps to maintain proper blood glucose levels by preventing excessive lowering of blood glucose. Thus, disruption of this hormone may result in hypoglycemia.