The stomach is an expanded portion of the gastrointestinal tract or GI tract that partially digests food by breaking it down mechanically and chemically in order to form a pulpy acidic fluid called chyme.
But the stomach is only divided into 3 histological regions: the cardia, fundus, and pylorus.
The cardia is a small area surrounding the opening to the esophagus which contains cardiac glands that secrete mucus.
This region of the stomach has fundic or gastric glands that secrete digestive enzymes such as pepsin, and a protective layer of mucus.
The pylorus is the most distal region of the stomach before reaching the pyloric sphincter.
This region will have a combination of pyloric glands that secrete mucus and neuroendocrine cells that secrete gastrin.
Similar to the rest of the GI tract, the wall of the stomach has 4 main layers: the inner mucosa, submucosa, muscularis propria, and outer serosa; although some portions of the GI tract have an outer layer of adventitia instead of serosa.
This low power longitudinal section of the stomach was taken from the cardia of the stomach.
Now, if we take a closer look at the mucosa of the cardia, we can see that the surface of the mucosa has a simple columnar epithelium with many invaginations that form millions of gastric pits.
The gastric pits will comprise about a quarter of the mucosa’s thickness.
The cardiac glands extend all the way to its underlying layer called the muscularis mucosa, which is a thin layer of smooth muscle that is still a part of the mucosal layer.
The next main layer of the cardia is the submucosa, which consists mostly of dense irregular connective tissue, but also contains larger blood vessels like the ones we can see in this image.
On the right of this image we can see a portion of the overlying mucosa and on the left is a portion of the next main layer called the muscularis propria.
The entire stomach’s muscularis propria is unique when compared to the rest of the GI tract because it has 3 layers of smooth muscle instead of only 2 layers.
In this image, we can see portions of the inner oblique layer on the right side of the muscularis propria, closest to the submucosa.
The middle layer is the circular layer, and the outer layer is a longitudinal layer of smooth muscle.
Because this tissue sample was sectioned longitudinally, the outer layer of smooth muscle is the layer that shows the long shape of the muscle fibers the best and the middle layer will have muscle cells that appear the most circular.
In this image the large blood vessels are easy to identify because of the red blood cells that can be seen within their lumens.
Alright, let’s move on to the fundic stomach.
This low power image allows us to see 3 of the main layers, the mucosa at the top, the submucosa, and the muscularis propria at the bottom.