Diagram of the Human Digestive System Poster

The whole digestive system is around 9 metres long. In a healthy human adult this process can take between 24 and 72 hours. Food digestion physiology varies between individuals and upon other factors such as the characteristics of the food and size of the meal. Phases of gastric secretion Cephalic phase - This phase occurs before food enters the stomach and involves preparation of the body for eating and digestion. Sight and thought stimulate the cerebral cortex. Taste and smell stimulus is sent to the hypothalamus and medulla oblongata. After this it is routed through the vagus nerve and release of acetylcholine. Gastric secretion at this phase rises to 40% of maximum rate. Acidity in the stomach is not buffered by food at this point and thus acts to inhibit parietal (secretes acid) and G cell (secretes gastrin) activity via D cell secretion of somatostatin. Gastric phase - This phase takes 3 to 4 hours. It is stimulated by distension of the stomach, presence of food in stomach and decrease in pH. Distention activates long and myenteric reflexes. This activates the release of acetylcholine which stimulates the release of more gastric juices. As protein enters the stomach, it binds to hydrogen ions, which raises the pH of the stomach. Inhibition of gastrin and gastric acid secretion is lifted. This triggers G cells to release gastrin, which in turn stimulates parietal cells to secrete gastric acid. Gastric acid is about 0.5% hydrochloric acid (HCl), which lowers the pH to the desired pH of 1-3. Acid release is also triggered by acetylcholine and histamine. Intestinal phase - This phase has 2 parts, the excitatory and the inhibitory. Partially digested food fills the duodenum. This triggers intestinal gastrin to be released. Enterogastric reflex inhibits vagal nuclei, activating sympathetic fibres causing the pyloric sphincter to tighten to prevent more food from entering, and inhibits local reflexes. Image reproduction rights can be found in the link near the bottom of this description. Sign up to Mr. Rebates for FREE and save 12% on any zazzle order in addition to a $5.00 sign up bonus All Rights Reserved; without: prejudice, recourse or notice (U.C.C. 1-308) Image Reproduction Rights: http://en.wikipedia.org/wiki/File:Digestive_system_diagram_edit.svg digestion "digestive system" diagram digestion+system digestion+diagram digestive+system digest gastrointestinal+tract human+digestive+tract digestion+system "digestive system diagram"