Lunch break

I’m about to break away from my lab bench and go eat lunch. And in doing so, I will be putting to use a part of my body I don’t think about very often – my stomach. Being curious in nature, I wondered - chemically and biologically speaking, how does the stomach work?

The stomach is the second stop in your body’s gastrointestinal tract (the first being your mouth), and it is designed to break down large food molecules into smaller ones that can be absorbed by your small intestine. It achieves this primarily because it is a balloon filled with acid. Acidity is measured on a pH scale, ranging from 0 to 14 - the lower the number, the more acidic a liquid is. A liquid is considered neutral – neither acidic nor basic – at a pH of 7. Everything above 7 is basic, while everything below 7 is acidic. Here are some examples of the pH of commonly encountered liquids:
-chlorox bleach = 11.4 (base)
-pure water = 7 (neutral)
-lemon juice = 2 (acid)
-sulfuric acid = 0.3 (strong acid).
The pH of your stomach varies between 1 and 4, depending on several factors including the time of day and what foods have been eaten. And the culprit responsible for this acidity? Gastric acid.

Gastric acid is one of the main secretions of the stomach. It is made up mostly of hydrochloric acid, along with small amounts of salts, and is secreted by a specific type of cell in the stomach, called parietal cells. The gastric acid serves to break apart large molecules like proteins. This strong acid in your stomach poses a potential difficulty for your body – if any of that acid was to escape the stomach, it would wreak havoc with whatever it touched. Anyone who experiences heartburn knows what this feels like! Heartburn occurs when acid from the stomach makes its way into the esophagus. The burning sensation is, actually, the stomach acid burning the lining of your esophagus. Your stomach, therefore, must have a strong acid-proof barrier to keep all of the gastric acid contained. That barrier is the stomach lining – actually, those cells called secretory epithelial cells.

Of the 4 major types of secretory epithelial cells lining your stomach, the mucous cells are the primary defense. They protect everything else from the gastric acid by secreting mucus - a basic, thick, sticky fluid. Actually, there are mucousal cells lining all of the body cavities that are exposed to the external environment – not only the stomach, but also places such as the nostrils and mouth. The mucus in your stomach neutralizes the acid before it eats away the cells underneath.

The mucous cells lining your stomach are actually organized several layers thick. The cells at the top (closest to the acid) are simple columnar epithelial cells. That means that they are shaped like cubes, taller than they are wide, stacked one layer thick, tightly packed together without any gaps. The cells are strictly oriented with a top and a bottom based on their connections with each other and with the cells underneath. Though they are protected from the stomach acid by the layer of mucus on their tops, they still live a harsh – and short – life. Your stomach lining, in fact, has of the most rapidly dividing population of cells in your entire body – the mucosal cells are replaced approximately every 20 hours.

What happens if the mucous cells can’t produce enough mucus to protect themselves from the stomach acid? The result is called a gastric ulcer. Gastric ulcers (which are ulcers specifically in the stomach, as opposed to peptic ulcers, which take place in the small intestine) are most commonly the result of an infection by the bacteria Helicobacter pylori. When H. pylori establishes an infection in your stomach, it produces compounds preventing the production of mucus. No mucus, no protection, and damage to the lining of your stomach can result. The good news, though, is that your stomach has amazing regenerative powers. Removal of the bacteria results in the regeneration of mucus and the mucousal cells.

I haven’t even touched on the rest of digestion, such as how nutrients get absorbed into the bloodstream and how the intestines work, and already I’m impressed. The stomach is an amazing organ that has to face a lot of challenges just to accomplish its job. Makes me appreciate it all the more!

Okay, enough about the stomach. I'm hungry.