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Organ system histology
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Although different parts of the tract may appear to have very different structures and functions, the wall still maintains 4 main layers all throughout the GI tract: the mucosa, submucosa, muscularis propria, and either an outer serosa or adventitia.
Even in this low power cross-section of the esophagus, we can see the inner mucosa, submucosa, and muscularis propria, although the outer adventitia isn’t present in this image.
All 4 layers have variations to their structure and function in different regions of the GI tract, but the mucosa is the layer that typically has the most significant changes.
The mucosa of the esophagus consists of 3 main layers.
At 20x magnification, we can see each of the layers more clearly.
The epithelium, lamina propria, and muscularis mucosa.
The thick epithelial layer lines the lumen of the esophagus and consists of stratified squamous non-keratinized cells, which has their typical appearance of flat, overlapping cells that are more flat as they move away from the base or basal cell layer.
The lamina propria is a much thinner layer of dense irregular connective tissue.
It provides a supporting function to the epithelium, such as the blood vessels within the connective tissue that supply blood to the epithelium.
The muscularis mucosa is the outermost layer of the mucosa and is comprised of smooth muscle.
The lower esophageal sphincter or LES for short is actually not an anatomical sphincter, which means histologically, there is no well-defined thickening or muscle that controls the LES.
Instead, the LES is considered a physiological or functional sphincter.
But when this sphincter isn’t functioning properly, it can lead to gastric acid reflux into the lower esophagus, which can cause heartburn.
Also, over time, prolonged exposure to gastric acid can cause damage to the epithelium of the esophagus.
The body attempts to adapt by transforming the normal stratified squamous cells of the lower esophageal lining into a mucus-secreting epithelium with simple columnar cells, which are better at protecting itself from gastric acid.
The esophagus is a muscular tube that carries food and liquids from the pharynx to the stomach. It has four layers of tissue, which are the mucosa, the submucosa, the muscularis propria, and either the serosa or adventitia.
The mucosa is a thin layer of cells that line the inside of the esophagus, and has glands that secrete mucus that protect the lining of the esophagus and keeps it moist. Beneath lies the submucosa that consists of connective tissue that supports the mucosa, and contains blood vessels, lymphatic vessels, and nerve endings. Next, lies the muscularis propria consisting of smooth muscle tissue that contracts to move food and liquids through the esophagus. Finally, comes the adventitia, which is the outer layer of the esophagus, which takes the name of serosa in the abdominal cavity after it's covered by the visceral peritoneum.
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