Digestive System

Week of April 30th 2009 we are covering the digestive system. The alimentary canal (GI tract) extends from the mouth to the anus. 6 processes of the digestive system: ingestion, secretion, mix and propel, digestion, absorption and defecation. GI tract has 4 layers: 1. Mucosa-the inner most layer which is avascular. Compromised of simple columnar epithelial cells. 2. Submucosa-highly vascular, may contain glands and lymphatic tissue and is composed of areolar connective tissue. An extensive network of neurons known as the submucosal plexus is found in this layer. 3. Muscularis-consists of circular, long and oblique fibers and is smooth muscle. The myenteric plexus, a network of axons that branch from the Vagus nerve X, are found between the layers of the muscularis. Peristalsis, wave like contractions, occur in this layer. 4. Serosa-portions of the GI tract suspended in the abdominopelvic cavity. Secretes a slippery, watery fluid that allows the tract to slide against other organs. Serosa is composed of simple squamous epithelium and areolar connective tissue and is part of the visceral peritoneum. There is a mechanical and chemical digestion that occurs. By way of peristaltic movements food is mixed in the stomach (mixing bag), these contractions allow the contact with HCl(hydrochloric acid). Specialized parietal cells, located in the mucosa, are plentiful with the enzyme carbonic anhydrase, this enzyme catalyzes the formation of carbonic acid,H2CO3, from water, H2O, and carbon dioxide, CO2. As it dissociates it provides a source of the H+ for proton pumps and generates the bicarbonate ions, HCO3, which after it builds up in the cytosol, will exchange for Cl- in the exchanger. Pumps powered by ATP actively transport H+ and K+ into the lumen of the stomach from the mucosa. The K+ will diffuse back into the mucosa while the H+ will free float in the lumen, at the same time Cl - will diffuse through Cl channels in to the lumen and free float in the lumen. The free floating H+ and Cl- bind HCl. Chief Cells, located in the mucosa, secrete pepsinogen, which is inactive so it will not digest the proteins in the chief cells that produced it. Once the pepsinogen comes in contact with HCl in the gastric fluids it converts to active pepsin which break apart big proteins making them smaller fragments.
Many family members included myself are taking medication to reduce stomach acids. I take Pepcid AC daily. Pepcid AC works by blocking a specific histamine receptor in the stomach. In the stomach histamine can cause the production of more acid, Pepcid AC reduces the amount of acid produced.