Gastroesophageal reflux disease (GERD)

Gastro- refers to the stomach, esophageal stands for esophagus, and reflux means “to flow back”.

So gastroesophageal reflux disease, or GERD, is when stomach acid flows back into the esophagus.

The presence of acid in the esophagus can lead to Barrett’s esophagus, a serious complication of GERD where the normal mucosa of the esophagus is replaced by one that’s similar to that of the intestines.

Barrett’s esophagus poses a higher risk of developing esophageal adenocarcinoma.

Normally, the wall of the entire gastrointestinal tract is made of 4 layers: the inner mucosa, the submucosa, a muscular layer, and an outer layer called the adventitia.

The mucosa is further divided into three layers - an innermost epithelial layer, a middle layer called the lamina propria, and an outermost layer, in contact with the submucosa, called the muscularis mucosae, which is made up of smooth muscle that contracts and helps with the breakdown of food.

Now, the stomach mucosa is different from the esophageal mucosa.

Inside the stomach, the epithelial layer is made up of cylindrical cells, which dive into the lamina propria, forming pits.

These pits are the gastric glands, and there are many of them scattered throughout the stomach.

Distributed among the cylindrical gland cells, there’s different types of secretory cells.

First, there’s G cells, which are a type of neuroendocrine cells that secrete a hormone called gastrin in response to food entering the stomach.

Gastrin stimulates another type of cells, the parietal cells, to release hydrochloric acid.

And then, there’s chief cells, which secrete an enzyme called pepsinogen.

Hydrochloric acid and pepsinogen are useful for digestion, but they can be quite aggressive for the delicate mucosa.

Luckily though, the stomach also has some defense mechanism in place.

First, the gastric glands also have foveolar cells, also called surface mucus cells, because they are closer to the surface of the stomach, and they secrete mucus.

Mucus is mostly made up of water and glycoproteins, and also bicarbonate ions which are also secreted by foveolar cells.

This bicarbonate-rich mucus protects the gastric mucosa from our own gastric acid, so it won’t get digested along with food.

Lastly the gastric mucosa is highly vascularized, which helps deliver oxygen and bicarbonate and carry away acid that makes it through into the lamina propria.

The esophagus, on the other hand, is better adapted for the passage of food. So its mucosa is made up of stratified squamous epithelium, which is better equipped to resist abrasion from food going down.