What kind of acid is in our stomachs? I’ve heard both Hydrochloric and Sulpuric. Which, if any, is right? Where do we get the raw materials to produce it (what foods do we need to eat specifically for that)?
Gastric juice has a high concentration of Hydrocholoric acid; I believe it is synthesized by the body from available materials. (There are free H[sup]+[/sup] and Cl[sup]-[/sup] in your body from different sources, e.g., natural salts, etc.)
Just to expand a little…from the UNM A&P course page
Gastric pits increase the surface mucosa for secretion and absorption. Specialized columnar epithelial cells release enzymes and other substances: zymogen (chief) cells release pepsinogen and parietal cells release hydrochloric acid. [IMPORTANT NOTE: Actually these cells secrete H+, derived from the same chemical reaction of CO2 and water which produces carbonic acid in the blood. The bicarbonate ions are retained and transported into the blood and the chloride ions are exchanged for them and pass into the stomach.] The H+ causes activation of the pepsinogen to produce the protease pepsin. Mucous neck cells and mucous surface cells (there are no true goblet cells in the stomach) produce an alkaline mucus which helps protect the lining from the acidity, which in the stomach reaches a pH from 1.5 to 3.5. Enteroendocrine cells produce a number of hormone substances including gastrin, histamine, endorphins, serotonin and somatostatin. Cells lining the gastric pits are arranged in circular acini in the stomach called gastric glands. These glands are found throughout the stomach and vary from one area to another with regard to their complement of cells.
How come your stomach doesn’t digest itself?
Wow, great info. Thanks!
That’s on the quote from Kinoons:
Otherwise, I guess it would digest itself.
What Joe_Cool said.
If the protective mucous cells are damaged, the stomach will in fact start “digesting itself.” This is called a peptic ulcer.
It has recently been found that such damage to the mucous cells is most often due to infection with the bacterium Helicobacter pylori.
More info:
http://www.med.umich.edu/1libr/topics/digest22.htm#causes
Well I’ve heard that a lot of things you eat are more acidic than your stomach acid… is that true?
Also, is 0 the lowest pH? i.e. the most acidic possible material?
Based on the info in kinoons’ link, stomach acid has a pH of 1.5 to 3.5. Many food and drink items, such as fruit juices and colas, have pH values that are less than 3.5, but nowhere near 1.5 (100 times more acidic).
Colas have a pH ranging from 2.4 to 2.8, due to the added phosphoric acid (a weak triprotic acid). This is the lowest pH that I found for a food or drink item.
Some info on acids in soft drinks:
http://www.britishsoftdrinks.com/htm/qa/ai_acids.htm
(BTW, a Google search on “pH soft drinks” brings up a whole lot of crap! :D)
There was a big discussion of this back in February. Simplistically speaking, you can theoretically have a pH less than zero, if you ignore difficult concepts such as activity (versus concentration). Any strong acid with a hydrogen ion concentration greater than 1 M will have a pH less than zero. However, considering activity (which virtually no General Chemistry class covers), the situation gets considerably more complicated, and there is no easy answer.
See this thread:
http://boards.straightdope.com/sdmb/showthread.php?threadid=60819
pH stands for percentage of hydrogen ions. An acid has an excess of H ions greater than a pH of 7. “7” is an inverse ratio: 1/10 [sup] 7 [/sup]. A pH of 0 then would be 1/10 [sup] 0 [/sup]. 10 [sup] 0 [/sup] is 1. Thus only a H ion can have a pH of 0/
No, it doesn’t.
In fact, the pX = -log(x) is used for many things besides hydrogen ion concentration, such as pOH, pK[sub]w[/sub], pK[sub]a[/sub], pK[sub]b[/sub], pC, etc.
See this for more info:
http://antoine.fsu.umd.edu/chem/senese/101/acidbase/faq/what-is-pH.shtml
What? 
The pH scale is based on the concentration (or activity) of hydrogen ions in an aqueous solution. All aqueous solutions contain some concentration of hydrogen ion.
[sub]No, I don’t want to hear about hydronium ion.[/sub] 
Isn’t the center of the pineapple supposed to be highly acidic and damaging to the stomach lining?
Jois
Acidic, yes. Highly acidic? Not compared to stomach acid. Damaging to the stomach lining? Not unless the person already has a pre-existing condition, such as an ulcer. It’s less acidic than cola (see above).
Some pH ranges are:
Source (also has the pH of a great many other foods):
http://vm.cfsan.fda.gov/~comm/lacf-phs.html
“Isn’t the center of the pineapple supposed to be highly acidic and damaging to the stomach lining?”
Perhaps you are confusing the pineapple’s acidity (not all that great) with its enzyme content. Pineapples do contain the enzyme bromelin which breaks down protein (and can be used as a meat tenderizer). I doubt that the bromelin effects the stomach lining but I can tell you from personal experience that eating two slices of fresh pinapple from a high-bromelin variety will make your tongue feel like it’s been scalded and eating half of such a pineapple will cause your tongue to bleed.
Thanks you, Yeah, that sounds right now that you say it. I remember hearing (as a kid) that “You don’t digest the center of a pineapple, it digests you” or something close to that. Maybe the grown ups knew what happened to the tongue and figured it would also happen in the stomach. The stomach lining is amazingly tough and oddly sensitive at the same time.
Jois