Bryan Hummel

                                                                                                            Vert. Physiology.

                                                                                                            December 11, 1999

Final Exam Questions

 

            First upon walking into Joe’s famous “Eat Here And Get Gas” corner store, restaurant and gas station, the wonderful smell of burning grease, and the sight of the dripping fries starts your body’s Cephalic gastric secretions.   Your stomach starts to ache.  You have an ulcer.  As discussed briefly in class, it may be caused by the bacteria Helicobacter pylori.  It is ones own stomach that causes the problem.  The stomach secretes HCl which causes its contents to become very acidic (1 to 2 pH).  Another culprit is the pepsinogen that is released from the chief cells and become activated pepsin upon exposure to the high acidity of the stomach contents.  These two secretions are used to digest food, but can digest their container (YOUR STOMACH) if not in check.  The gastric protease pepsin results in hydrolysis of proteins into polypeptides and since your stomach is made of proteins, it would be digested unless protected. 

            The internal layer of the stomach is lined with thousands of gastric pits, which are filled with gastric juices from the gastric glands.  In the gastric glands, the chief cells (zygomatic) secrete pepsinogen, the parietal cells secrete HCl (hydrochloric acid), and the goblet cells secrete mucus.  It is this mucus that acts to protect the stomach and it is a defect in mucus production, which leads some people to have ulcers and others not.  I do not know enough to definitively say that the bacteria Helicobacter pylori causes a defect with the goblet cells, but this may be a possibility.  

The treatment of ulcers is commonly undertaken with antibiotics along with antacids.  The antibiotics keep the Helicobacter pylori from causing any further problems and the antacids keep the pH of the stomach more neutral.  There are other methods of suppressing the acid production such as; cimetadine histamine blockers or omeprazole which inhibit H+ ATPase activity.  The cimetadine is effective because it takes histamine to stimulate HCl secretion from the parietal cells (by binding on the parietal cell membranes, page 654), and cimetadine acts as a histamine H2 receptor blocker, therefore no acid production.  The omeprazole, which inhibits H+ ATPase activity, prevents HCl formation by not allowing the H+ to leave the bloodstream to bind with Cl- in the parietal cells.  This also prevents the alkaline tide seen in most animals during digestion. Without an acidic environment, the pepsinogen cannot become activated and thus cannot digest the proteins (or your stomach).  Without acid inflaming the stomach or pepsin hydrolyzing it, your body has time to repair what has been harmed.

As for that pesky bacteria, apparently it has high levels of urease on its surface.  The urease breaks down urea and forms CO2 and Ammonia.  Urea is a by-product of animal metabolism, and it is toxic to most animals including bacteria.  High levels of urea tend to cause the break up of proteins into constituent subunits, and most all nitrogenous wastes are harmful especially ammonia.  The bacteria with its urease enzyme may seem to be hurting itself by the production of ammonia (NH3), but it probably hurts the stomach even more (in other words, I don’t know how that could possibly be beneficial to the bacteria to be living in a poison). 

 

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