Stomach histology

Stomach wall

The stomach wall consists of 4 layers of tissue. From deep (external) to superficial (internal) these are the serosa, muscularis externa, submucosa and mucosa. This layered arrangement follows the same general structure in all regions of the stomach, and throughout the entire gastrointestinal tract. The outer layer of the stomach wall is smooth, continuous with the parietal peritoneum. The inner wall (mucosa and submucosa layers) is thrown into folds known as rugae, or gastric folds, which allow the stomach to distend upon the entry of the food. A bolus of food enters the stomach from the esophagus. The various tissue layers of the stomach wall then combine their functions to digest the bolus into a viscous, pulpy fluid called chyme. Chyme is directed into the duodenum of the small intestine for further digestion and absorption.

You can easily remember the four layers of the stomach wall using the mnemonic 'M.S.M.S'. It stands for: Mucosa, Submucosa, Muscularis externa & Serosa.

Although the stomach is anatomically divided into four regions, histologically we identify only three; cardia, fundus and pylorus. This is because the fundus and body are histologically identical. Let’s now take a closer look at the 4 layers of the stomach, as well as their regional variations.

Mucosa

The innermost layer of the stomach wall is the gastric mucosa. It is formed by a layer of surface epithelium and an underlying lamina propria and muscularis mucosae. The surface epithelium is a simple columnar epithelium. It lines the inside of the stomach as surface mucous cells and forms numerous tiny invaginations, or gastric pits, which appear as millions of holes all throughout the stomach lining. These gastric pits are important as they are connected to the various glands of the stomach.

There are 3 types of glands found in the stomach; cardiac, gastric and pyloric, named after the region in which they are found. These glands produce the digestive enzymes and mucous secretions of the stomach. The gastric glands of the fundus/body have the important role of producing digestive gastric juice while the cardiac and pyloric glands predominantly produce mucous secretions which protect the stomach from the harsh effects of the digestive acid and prevent stomach self-digestion.

Submucosa

Deep to the mucosa is a thick layer of connective tissue known as the gastric submucosa. Its arrangement means that it is durable, yet flexible and mobile. Aside from rich vasculature and lymphatics, this layer also holds the submucosal (Meissner’s) plexus. The nerve fibres of this plexus carry parasympathetic innervation to the blood vessels and smooth muscle of the stomach wall. Parasympathetic stimulation is associated with ‘rest and digest’ functions and therefore, stimulates digestion.

Muscularis externa

The gastric muscularis externa, also known as tunica muscularis, is the smooth muscle located deep to the submucosa. It is made up of 3 layers: inner oblique, middle circular and outer longitudinal. The muscularis externa layer produces churning movements required for mechanical digestion. When these layers contract, they throw the mucosa and submucosa into rugae.

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The arrangement of the muscularis externa varies between different stomach regions. In the cardia the layers are well-developed, creating a sphincter to prevent acid reflux from the stomach into the esophagus. In the fundus, the muscle is poorly developed as a lot less churning takes place in this region. The body is composed of all three muscle layers, except in the anterior and posterior parts of the stomach where the longitudinal muscle layer is largely absent. In the pyloric region the muscularis externa is well developed in order to propel chyme into the duodenum, while its thickened circular layer forms the pyloric sphincter.

Housed within the muscularis externa is the myenteric (Auerbach's) plexus, carrying both sympathetic and parasympathetic fibres to the smooth muscle layers. The neurons of this plexus are linked to smooth muscle cells through interstitial cells of Cajal (ICCs). As well as mediating neural signals, these cells act as intrinsic pacemakers of the gut controlling the slow contractions of the stomach wall required for churning of the food. The activity of ICCs is controlled by the autonomic nervous system.

As we mentioned previously, in addition to the myenteric (Auerbach's) plexus in the muscularis externa, we have a submucosal (Meissner’s) plexus in the submucosa. If you struggle remembering the difference between the two a mnemonic can help! Use SMP & MAPS, which stand for:

• Submucosal
• Meissner's
• Parasympathetic
  

• Myenteric
• Auerbach's
• Parasympathetic
• Sympathetic
  

You can learn more about the musculature of the stomach by diving into the following learning materials!

Serosa

Gastric serosa is the outermost layer of the stomach wall. It consists of a layer of simple squamous epithelium, known as mesothelium, and a thin layer of underlying connective tissue. The mesothelium produces serous fluid, which lubricates the outer wall of the stomach and ensures its smooth movement in the abdominal cavity. The serosa is continuous with the parietal peritoneum. It is absent at the attachment sites of the greater and lesser omenta to the stomach, as well as over a small superoposterior area near the cardiac orifice where the stomach is attached to the diaphragm via gastrophrenic and gastropancreatic folds.

 Now that you learned everything about the histology of the stomach, test and consolidate your knowledge with he quiz below!