chemical digestion uh we're going to have protein digestion beginning as the hydrochloric acid denatures or unfolds the protein molecules it transforms pepsinogen into pepsin and that's going to break peptide bonds and create smaller versions of the protein called peptides fat digestion is going to continue especially in the infant's stomach where the ph is 5 to 6 rather than 2.5 hydrochloric acid also helps to kill microbes in foods and the mucous cells protect the stomach walls we have about one to three millimeter thick inch layer of a thick layer of mucus in our stomach the mechanical digestion first starts as gentle mixing waves that occur every 15 to 25 seconds we produce about two quarts a day of gastric juice and that is going to combine with the bolus to make chyme which is a soupy soupy substance as the food is moving through the stomach you have more vigorous waves and then intense waves near the pylorus and again the pyloric sphincter will open and squirt out one to two teaspoons full with each wave it's important it does that rather than just open up and empty it because by allowing only small amounts to exit at any given time it allows those small amounts to have the most amount of surface area contact with the small intestine as it swirls through there vomiting is also called emesis and emesis is the forcible expulsion the contents of the upper gi tract sometimes it can even be from the duodenum and if you're vomiting from the duodenum you generally will get like a an alkaline taste in your mouth from it prolonged vomiting can be very serious you end up with acid-base problems because of loss of the acid from the gastric juice it also can lead to dehydration peptic ulcers are crater-like lesions they develop in the mucous membrane the gi tract in areas that are exposed to gastric juice uh one of the most common complications is anemia caused from bleeding three well-defined causes are the bacterium helicobacter pylori non-steroidal anti-inflammatory drugs like aspirin and hypersecretion of hydrochloric acid helicobacter pylori is a bacterium that can live in the acidic conditions of the stomach basically what it does is it goes in it invades down through the mucous layer to the epithelial cells where it converts urea and water it has a urease and it can convert this into ammonium ammonium is going to neutralize the acid and it creates an environment where now that this bacteria can live it's neutralized the acid so now it is able to live in this environment however the loss of acid as well as destruction by the of the mucosa allows the acid in the lumen as well as the pepsin to contact and damage the cells in the mucosa and so these cells die cytotoxins kill them as well as ammonia so the different types of things that can happen from an infection with helicobacter pylori less than one percent uh are going to develop a type of lymphoma malt that's mucosa associated lymphatic tissue uh lymphoma uh 100 of people that are infected with it and it was some kind of acute or chronic gastritis which is an inflammation of the gi of the stomach some about five percent will have gastric atrophy one percent will develop gastric cancer and about 10 percent will develop either a gastric ulcer or a duodenal ulcer in the very beginning of the duodenum uh this was really a controversial discovery that that most of these um peptic ulcers are created by helicobacter pylori it was thought back in the 70s and before then that eating acidic foods being stressed all of those types of things are what caused ulcers to form but as time went on there was research done by two australian scientists barry marshall and robin warren and they identified helicobacter pylori in 1982 as the cause of most gastric ulcers and for that they won the nobel prize in 2005 in physiology and medicine this was controversial because no one believed that bacteria could live in such an acidic environment and while marshall and warren were studying these ulcers they noticed that whenever they did biopsies they were finding this bacterium and they wondered whether the bacterium itself was causing it the culture at the time was such that they were pretty much laughed out of the business um they couldn't get funding they couldn't get their papers published uh there was also strong input from the pharmaceutical companies who had developed lots of antacid type preparations things like proton pump inhibitors that decrease hydrogen ion formation as well as different types of treatments for ulcers and acidic stomach and if someone's on that they're on that for life if someone has a bacterial infection that's causing a problem you give them 10 worth of antibiotics and they're done so there was also a lot of pressure from the pharmaceutical companies not to accept these findings however even though they couldn't get funding they couldn't get their papers published dr marshall was sure that it was this bacteria so he did something that's frowned upon in science and that is he experimented on himself he drank a beaker with a culture of helicobacter pylori and then waited to develop the signs of gastritis and he did and was able to culture cells the bacteria from his stomach so he proved the proof of his his principle there that helicobacter pylori causes um and is not a byproduct of an ulcer it causes the ulcer in some areas of the world helicobacter pylori infections are associated with cancer gastric cancer and part of it is determined by when you become infected with it if you're infected with it asymptomatically as a child you stand a greater chance of developing gastric cancer if you're infected with it as an adult you stand a greater chance of developing an ulcer this was from um a comic book that was made showing um dr warren drinking this beaker with a bacterial culture in it he is the only nobel prize winning scientist to have his own comic book the goals for this lecture are to draw a stomach label the different regions describe the mechanical and chemical digestion that occurs in the stomach lists all the enzymes and other substances and gastric juice that contribute to digestion describe the histology of the gastric mucosa defined chyme pyloric stenosis pylorospasm parietal cell chief cell g cell gastrin zollinger ellison syndrome peptic ulcer and emesis