Regulation of Pancreatic Secretion

The nervous and endocrine systems regulate release of pancreatic juice, much as they regulate gastric and small intestinal secretions. For example, during the cephalic and gastric phases of gastric secretion, parasympathetic impulses stimulate the pancreas to release digestive enzymes. A peptide hormone, secretin, stimulates the pancreas to secrete a large quantity of fluid when acidic chyme enters the duodenum. Secretin is released into the blood from the duodenal mucous membrane in response to the acid in chyme. The pancreatic juice secreted at this time contains few, if any, digestive enzymes but has a high concentration of bicarbonate ions that neutralize the acid in chyme (fig. 17.25).

In cystic fibrosis, abnormal chloride channels in cells in various tissues cause water to be drawn into the cells from interstitial spaces. This dries out secretions in the lungs and pancreas, leaving a very sticky mucus that impairs the functioning of these organs. When the pancreas is plugged with mucus, its secretions, containing digestive enzymes, cannot reach the duodenum. Individuals with cystic fibrosis must take digestive enzyme supplements — in capsule or powder form that can be mixed with a soft food such as applesauce—to prevent malnutrition.

Proteins and fats in chyme in the duodenum also stimulate the release of the hormone cholecystokinin from the intestinal wall. As in the case of secretin, chole-cystokinin reaches the pancreas by way of the bloodstream. Pancreatic juice secreted in response to

. Acidic chyme enters duodenum

5. Pancreatic juice, high in bicarbonate ions, neutralizes acidic chyme

2. Secretin released into bloodstream from intestinal mucosa

. Acidic chyme enters duodenum

5. Pancreatic juice, high in bicarbonate ions, neutralizes acidic chyme

2. Secretin released into bloodstream from intestinal mucosa

Turtle Pancreas

4. Pancreas secretes pancreatic juice

Secretin stimulates pancreas

Figure

Acidic chyme entering the duodenum from the stomach stimulates release of secretin, which in turn stimulates release of pancreatic juice.

4. Pancreas secretes pancreatic juice

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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