proposed_essay_questions_2008

proposed_essay_questions_2008 - Bio G 110 Prelim I Spring...

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Bio G 110 Prelim I Spring 2008 Two of the following essays will appear on the First Prelim. Essay 1: How did Robin Warren and Barry Marshall demonstrate the cause of ulcers? Until recently, gastric ulcers were thought to be caused by stress or spicy food. Robin Warren noticed that many of his patients with stomach problems had a spiral- shaped bacteria associated with the epithelium of the stomach. The bacterium is acid tolerant, lives in the mucus layer of the stomach and produces chemicals that make holes in (i.e. ulcerates) the stomach wall. Barry Marshall tried to culture spiral-shaped Helicobacter pylori without success. During Easter vacation, he accidentally left the cultures in the incubator (longer than the typical 48 h they had been culturing the bacteria for). When he returned from vacation, he noticed that the plates contained numerous colonies of the same helical bacterium that Warren had observed. The bacteria must be present in every case where you find the disease. Koch Postulate The bacteria must be isolated from the host and grown in pure culture. The specific disease must be induced into a healthy host when a pure culture of the bacterium is inoculated into it. The bacteria must be recovered from the experimentally infected host. Warren and Marshall tried to fulfill Koch’s third postulate, but they could not find an animal model to see if they could induce gastric ulcers in the test animal. Without an animal model, Marshall decided to drink a bacterial culture containing Helicobacter . He successfully induced a severe inflammation of the stomach and then cured it with antibiotics. Helicobacter pylori causes 80% of gastric ulcers. These can be cured with antibiotics . Only 10-15% of the people infected with Helicobacter get ulcers, so there may also be a genetic or environmental component. Stress-induced acid secretion causes 20% of the gastric ulcers. These ulcers can be prevented though lifestyle changes and/or treated with medications that interfere with acid secretion.
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proposed_essay_questions_2008 - Bio G 110 Prelim I Spring...

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