The Regulation of Digestion

<h1>Text Preview</h1> <p>Digestion is regulated by signals from nerves in the spinal cord and brainstem that connect to the digestive organs. These nerves don’t interact with the conscious brain at all. In fact, brainstem connections and spinal cord connections often work in opposite ways. </p> <p>Suppose you’re sitting at home waiting for a tasty meal to cook. Your brainstem signals your stomach to start secreting digestive enzymes, your liver is stimulated to release bile, and you begin salivating. Suddenly, you smell smoke from the kitchen—your house is on fire! </p> <p>Your spinal cord nerves take over and you jump up. Your mouth goes dry as the saliva flow is inhibited. Nerve impulses pass to the stomach, which shuts down digestion temporarily, and a hormone released from the brain stimulates your liver to quickly convert glycogen to glucose, anticipating that you might need energy in a hurry!</p> <p>How do these nerve impulses affect the digestive system?</p> <p>Nerve pathways from the spinal cord and brainstem connect to networks of nerve fibers embedded in the lining of the digestive tract from the esophagus to the anus. These fibers control the motility of the digestive system, as well as the blood flow into and out of intestinal cells. The presence of food in the stomach and small intestine stimulates the release of several hormones. </p> <p>This is the role of the endocrine system in the digestive process. In the stomach, food stimulates the production of gastrin, a hormone produced by the cells of the stomach wall. Gastrin, in turn, stimulates the production of more gastric juice.</p> <p>In the small intestine, the hormone cholecystokynin, or CCK, is released when peptides and fats are present. CCK stimulates the flow of the pancreatic enzymes and also makes the gallbladder contract to release more bile. Cholecystokynin literally means “bile sac mover.”</p> <p>A third hormone, secretin, plays an important role in protecting the intestines from damage by the acidic chyme that leaves the stomach. The presence of acid in the small intestine stimulates the endocrine cells of the intestinal epithelium to secrete secretin. Secretin stimulates the pancreas to produce a bicarbonate-rich fluid and secrete it into the intestine. The bicarbonate neutralizes acid, providing negative feedback and removing the stimulus for the release of more secretin. </p> <p id="TextCopyright">Copyright 2006 The Regents of the University of California and Monterey Institute for Technology and Education</p>