ESOPHAGUS
Long, muscular tube delivers food from the pharynx to the stomach.
- Mucosa layer
- Comprises stratified squamous epithelium; layers of flattened cells provide protection against physical and chemical damage from the foods, liquids, and salivary juices traveling to the stomach.
- Muscularis mucosae is also visible in our sample.
- Submucosal layer
- Submucosal glands
- Glands of the submucosal and mucosal layers produce protective and lubricating mucous, which contributes to the protective barrier.
- Submucosa and mucosa form longitudinal folds in the relaxed esophagus; these folds expand to accommodate foods and liquids during swallowing.
- Muscularis externa layer
The composition of the muscularis externa layer changes along its length, as follows:- The upper 1/3rd comprises skeletal muscle fibers in both the circular and longitudinal layers;
- The middle 1/3rd comprises a circular layer of skeletal muscle and a longitudinal layer of smooth muscle;
- Both layers of the lower 1/3rd, which opens to the stomach, contains smooth muscle fibers.
- The outermost layer of the esophagus is adventitia; once the esophagus passes through the diaphragm, and is no longer anchored to the body wall, it becomes serosa.
STOMACH
Connects with the esophagus, superiorly and the duodenum, inferiorly.
Regions of the stomach:
- Cardiac, where the esophagus and stomach meet
- Fundus, in the upper left corner
- Body, which is the largest region of the stomach
- Pyloris, which opens to the duodenum
Gastric Folds, aka, rugae - Line the empty stomach; expand to accommodate foods and liquids during gastric filling
Histological Details: - Surface mucous epithelium
- These cells secrete mucous and form a physical and chemical barrier to protect the underlying stomach wall from stomach contents. In addition to ingested foods and liquids, the stomach wall is potentially vulnerable to the gastric juices it releases as part of digestion.
- Pits
- Invaginations of the surface mucosal epithelium form pits, which open to glands deeper within the mucosa; depending on their location in the stomach, the glands produce mucous and/or gastric juices.
- Lamina propria is visible in our sample between the pits and glands.
- Slips of muscularis mucosae can be seen extending into the gastric fold.
Glands:
- Cardiac and pyloric glands are primarily mucous-secreting; in other words, they do not produce significant quantities of gastric juices.
- Cardiac glands are highly coiled at their ends, or bases.
- Pyloric glands are highly branched.
- Gastric glands of the fundus and body produce both mucous and gastric juices; they are responsible for chemical digestion.
- Surface epithelial cells line the pit, and secrete surface mucous.
- Mucous neck cells also secrete mucous.
- Parietal cells, which appear as round, bulging, and light pink in the histological sample, are found within the neck and base of the gastric gland. These cells, which are also referred to as oxynitic cells, secrete hydrochloric acid and intrinsic factor (required for vitamin B12 absorption).
- Stem cells are also found within the neck; these cells play important roles in the constant renewal of gastric mucosal cells.
- Chief cells reside in the base of the gland, and stain darker due to secretory granules containing pepsinogen, which is a precursor to pepsin for protein digestion.
- Enteroendocrine cells, which is an umbrella term for a variety of cells that secrete peptide hormones. For example, G cells secrete gastrin, and D cells secrete somatostatin.
- The cells of the gastric gland lie on a basement membrane, which separates them from the surrounding glands and lamina propria.
