Your Stomach Juices Are So Acidic They Can Digest Zinc And Meat. So Why Don't They Digest You And Your Precious Organs?

But why does your stomach not digest itself? This question has been around since we first began messing around with gastric juices, and noticing that it was capable of digesting meat, and the tissue of some unfortunate live frogs. First, we're taking a small detour because, honestly, you really need to know the disgusting ways we figured this stuff out. 

Before proper scientific investigation into the issue, there was a debate as to whether the stomach digestion was a chemical or mechanical process, involving the churning of whatever food you have sent down your mouth hole. In 1822, we got our first proper answer to this question, thanks to an 18-year-old trader from Canada named Alexis St Martin, who helpfully got himself shot in the stomach at point-blank range by a duck hunter, leaving him with a permanent hole in his stomach.

A curious window of opportunity 

Where some would see a lifetime of problems, local doctor William Beaumont saw a window of opportunity. Beaumont was able to save the man's life and decided to pay him to stick around for some pretty disgusting investigations into digestion. Throughout the course of St Martin's life, despite attempts by the poor man to escape from this unusual lifestyle, Beaumont would dip pieces of meat attached to a string into the man's stomach hole and retrieve them at different intervals to note the effect that it had. As well as this, he would take the occasional lick inside the hole to identify via taste when the stomach was particularly acidic. 

The full and disgusting story is worth checking out, but for now, let's just say this: it was confirmed that digestion in the stomach was largely chemical, aided by the churning and mixing motions within it. After chewing and swallowing, highly acidic juice inside your stomach goes to town on your meal.

"Pure gastric juice as it is secreted by the fundic glands and free from admixture with food or swallowed saliva is an exceedingly corrosive liquid," surgeon Lester Reynolds Dragstedt explained in a 1961 paper on the topic. "It has the capacity to destroy and digest all living tissue, including the highly resistant mucous membrane of the stomach and small intestines."

Whilst we know that these juices are capable of digesting meat, the way we found this out was through experimentation, on top of those performed by Beaumont. For example, Dragstedt himself collected gastric juice from Pavlov pouches (the Pavlov's dog experiment, too, may be far more disgusting than you imagine) before taking living frogs and dangling their legs in the juice. 

Though the frogs remained alive, they did not have a spectacular time, as their legs were digested by the mix of pepsin and hydrochloric acid, with hydrochloric acid found to be the most critical of the two substances.

So, if it's so acidic and destructive, why does your stomach not digest itself? 

Sometimes it does...

"One answer, of course, is that it sometimes does. Under certain circumstances, gastric juice can produce ulcers and even destroy most of the stomach lining," another paper on the topic explains. "Normally, however, the stomach wall staunchly resists attack; as Claude Bernard observed, it behaves as if it were made of porcelain."

Undiluted gastric juice is highly corrosive, and if your other organs, such as your pancreas, spleen, intestines, as well as the mucosa of your stomach, are exposed to it, then they're going to get digested like a laboratory frog. But in healthy individuals, your mucosa does not get digested by your own gastric juice as it is diluted by the various foods and liquids you've put in there.

"The mechanism which regulates gastric secretion provides for an abundant flow of gastric juice when food is in the stomach and also checks further secretion before the gastric content becomes sufficiently corrosive to damage the mucosa," Dragstedt explained.

Basically, the stomach's role is to break down food into smaller pieces so we can absorb it. The main component of gastric juice is hydrochloric acid, a chemical so strong it can dissolve metal. To stop this acid from corroding the stomach's walls, the epithelium (cells that line the inside of the stomach) secretes a thick alkaline mucus, rich in bicarbonate, to combat the acid and protect the stomach. This mucas covers the stomach walls and is continually renewed by the epithelium for sustained protection.

However, as Dragstedt pointed out, "Pure gastric juice can destroy the mucosa and produce a peptic ulcer. An ulcer forms when gastric secretion is stimulated by agencies other than food and when its buffering effect is absent or inadequate."

In short, your body has a method of diluting your juices so that you don't digest yourself. But sometimes, when things go wrong, you do digest a little of yourself anyway.