From the Guidelines
The histology of the GI tract is characterized by a four-layer organization with specific adaptations for each region, including variations in the mucosa layer such as stratified squamous epithelium in the esophagus, simple columnar epithelium in the stomach, and villi and crypts in the small intestine. The GI tract's histological features are distinct in each region, with the esophagus having stratified squamous epithelium for protection against abrasion, as seen in the context of Barrett's oesophagus diagnosis 1. In contrast, the stomach mucosa features simple columnar epithelium with gastric pits containing specialized cells such as parietal cells, chief cells, and mucous cells. Key features that distinguish the oesophageal origin of biopsy specimens include the presence of submucosal oesophageal glands, multi-layered epithelium, or squamous islands, which are helpful in diagnosing Barrett's oesophagus 1. Some of the main characteristics of each region include:
- Esophagus: stratified squamous epithelium
- Stomach: simple columnar epithelium with gastric pits and specialized cells
- Small intestine: villi and crypts with absorptive enterocytes, goblet cells, enteroendocrine cells, and Paneth cells
- Large intestine: numerous goblet cells for lubrication and lack of villi. The submucosa and muscularis externa also have distinct features, including Meissner's plexus and Auerbach's plexus, which play crucial roles in the GI tract's function 1.
From the Research
Histology of the GI Tract
The GI tract is a complex system with various layers and cell types. The histology of the GI tract can be differentiated into several sections:
- Esophagus: The esophagus is lined with stratified squamous epithelium, which provides protection against mechanical stress and acid reflux 2.
- Stomach: The stomach is lined with simple columnar epithelium, which contains glands that secrete digestive enzymes and acid. The stomach mucosa is also home to various cell types, including chief cells, parietal cells, and enterochromaffin cells 3, 4.
- Small intestine: The small intestine is lined with simple columnar epithelium, which contains microvilli that increase the surface area for absorption. The small intestine is also home to Paneth cells, which produce antimicrobial peptides 4.
- Large intestine: The large intestine is lined with simple columnar epithelium, which contains goblet cells that produce mucus. The large intestine is also home to various cell types, including enterocytes and enterochromaffin cells 4.
Layers of the GI Tract
The GI tract is composed of several layers, including:
- Mucosa: The mucosa is the innermost layer of the GI tract, which comes into contact with food and digestive enzymes. The mucosa is lined with epithelial cells and contains glands that secrete digestive enzymes and acid 3, 4.
- Submucosa: The submucosa is a layer of loose connective tissue that supports the mucosa and contains blood vessels and nerves 4.
- Muscularis: The muscularis is a layer of smooth muscle that contracts and relaxes to mix food and move it through the GI tract 4.
- Serosa: The serosa is the outermost layer of the GI tract, which is composed of visceral peritoneum and attaches the GI tract to surrounding organs 4.
Cell Types in the GI Tract
The GI tract is home to various cell types, including:
- Chief cells: Chief cells are found in the stomach and secrete pepsinogen, which is converted to pepsin in the presence of acid 3, 4.
- Parietal cells: Parietal cells are found in the stomach and secrete hydrochloric acid, which creates an acidic environment for digestion 3, 4.
- Enterochromaffin cells: Enterochromaffin cells are found in the stomach and small intestine and produce serotonin, which regulates gut motility and secretion 3, 4.
- Goblet cells: Goblet cells are found in the large intestine and produce mucus, which lubricates the passage of food and protects the epithelium from damage 4.