Histology of the Esophagus and the Stomach Flashcards
What are the four different layers of the GI tract?
the mucosa, the submucosa, the muscularis externa, and the serosa/adventitia
which layer of the GI tract varies from region to region?
the mucosa
what are the three components of the mucosal layer of the GI tract?
the lining epithelium, the lamina propria, and the muscularis mucosae
what makes up the lamina propria?
vascularized loose connective tissue
what is found within the lamina propria?
lymphatic nodules and WBCs
what is the muscularis mucosae and what is its role?
it is a layer of smooth muscle that moves the mucosal layer that sits directly above it
what is the submucosal layer made up of?
dense irregular connective tissue with neurovasculature and lymphatics- glands can also be present in specific parts of the GI tract
what makes up the muscularis/ muscularis externa layer?
two layers of smooth muscle
what are the two layers of smooth muscle that make up the muscularis layer of the GI tract?
the inner circular layer and the outer longitudinal layer
contraction of the circular layer does what?
it constricts the lumen
contraction of the longitudinal layer does what?
it shortens the tube
how do you get a serosa layer?
when the GI tract is suspended by mesentery, the adventitia is covered by mesothelium and that forms the serosa
what are areas without a mesothelium covering called?
adventitia
What are the 4 main functions of the different mucosal types?
protective, secretory, absorptive, and absorptive/protective
what epithelium makes up the protective mucosa?
nonkeratinized stratified squamous epithelia
where is the protective mucosa found?
in the oral cavity, the pharynx, and the anal canal
what epithelium makes up the secretory mucosa?
simple columnar epithelium
where is the secretory mucosa found
in the stomach
what epithelium makes up the absorptive mucosa?
simple columnar epithelium
how is absorptive mucosa arranged?
as villi with crypts
where is absorptive mucosa found?
small intestine
what epithelium makes up the absorptive/protective mucosa?
simple columnar epithelium
how is the absorptive/protective mucosa arranged?
closely packed glands with goblet cells
where is the absorptive/protective mucosa found?
large intestine
we have two plexus that are responsible for regulating movements and secretions in the GI tract. What are they?
submucosal plexus of Meissner and myenteric plexus of Auerbach
where is the submucosal plexus of meissner positioned?
just deep to the submucosal layer of the GI tract- sits in between the submucosal layer and the muscularis layer
where is the myenteric plexus of Auerbach positioned?
it sits in between the inner and outer layers of the muscularis externa
what are the enteric plexuses responsible for?
they are responsive to local stimuli and input from the ANS; they regulate and control peristaltic contractions and secretory activities
does the esophagus have a serosa layer or an adventitia layer?
both; the thoracic esophagus has adventitia and inferior to the diaphragm the esophagus has a serosa layer
what glands are found in the esophagus?
mucosal and submucosal glands produce a thin layer of mucus to lubricate the epithelium
what gland is found in the lamina propria of the esophagus?
cardiac esophageal glands- in the terminal esophagus
what epithelium is found in the mucosal layer of the esophagus?
nonkeratinized stratified squamous epithelium
what is found within the submucosal layer of the esophagus?
the submucosal venous plexuses
what do the submucosal venous plexuses drain into?
the systemic and portal venous systems
the submucosal venous plexuses can become inflamed and increase pressure within the portal venous system which can cause what?
esophageal varices
what muscle makes up the muscularis layer of the upper third esophagus?
skeletal muscle (striated)
what muscle makes up the muscularis layer of the middle third esophagus?
skeletal and smooth muscle
what muscle makes up the muscularis muscle of the lower third of the esophagus?
smooth muscle
what is the role of the lower esophageal sphincter?
it prevents reflux of gastric contents
what is caused by a weakening of the lower esophageal sphincter?
GERD
what can GERD cause?
chronic inflammation, ulceration, and dysphagia due to reflux of gastric contents
what happens when GERD becomes a chronic issue?
the non-keratinized stratified squamous epithelium of the esophagus is in a transition zone and it will become columnar mucus secreting/ glandular
what is the chronic form of GERD known as?
Barrett’s esophagus
what is the epithelial transition from the esophagus to the stomach known as?
the gastroesophageal junction
what does the non-keratinized stratified squamous epithelium become when transitioning to the stomach?
simple columnar epithelium
how is the epithelium in the stomach characterized?
glandular, with pits and glands
what are the four regions of the stomach?
cardia, fundus, body, and pyloris
what is rugae?
longitudinal folds of the gastric mucosa that expand during filling of the stomach
what are rugae covered by?
gastric pits, which are openings into gastric glands
what is found within the gastric glands?
the different cell types that we need in order to secrete the products necessary to produce our gastric contents
where are the cardiac, gastric, and pyloric glands found in the stomach?
in the lamina propria of the mucosal layer
what facilitates the release of the gastric gland secretions?
the muscularis mucosae in the mucosal layer
what makes up the muscularis layer of the stomach?
3 layers of smooth muscle: oblique, circular, and longitudinal
what forms the pyloric sphincter?
the circular muscle layer thickening in the pyloric region
what are the characteristics of the gastric glands?
simple, branched, tubular glands
what are the three parts of the gastric glands?
the gastric pit, the isthmus/neck, and the gastric gland (the base)
what are the cells that line the gastric glands?
mucosal cells, chief cells, parietal cells, enteroendocrine cells
there are two different types of mucous cells. What are they?
surface mucous cells and mucous neck cells
where are surface mucous cells located?
they line the lumen and gastric pits
where are the mucous neck cells located?
they are located in the neck of the gastric gland in singles or clusters
what do mucous cells secrete?
a mucous layer containing 95% water and 5% mucin
what is the purpose of mucous?
it serves as a thick coating that neutralizes the microenvironment to an alkaline pH
where are chief (zymogenic) cells located?
they are found in clusters in the inferior 1/3 of gastric glands
how can you identify chief cells on a histologic stain?
they have an abundant RER and apical secretory (zymogen) granules; dark staining cytoplasm
what do chief cells secrete?
pepsinogen
what is pepsinogen?
the proenzyme that is stored in secretory granules; when it is released it is converted to pepsin by the acidic environment
what is the role of pepsinogen/pepsin?
it is a proteolytic enzyme that digests most proteins
what is exocytosis of pepsinogen stimulated by?
feeding
what else can chief cells produce and what is the role?
gastric lipase, which digests many lipids
where are parietal cells found?
they are predominately found near the neck and upper segment of the gastric gland
what do parietal cells produce?
hydrochloric acid and intrinsic factor
what is intrinsic factor?
a glycoprotein that binds to vitamin B12
what are the hallmarks of parietal cells?
large cells, usually round or pyramidal-shaped, one (sometimes two) central round nucleus, cytoplasm is eosinophilic due to increased mitochondria
what is the deep invagination of the apical plasma membrane that is found within active parietal cells?
intracellular canaliculus- increases the surface area
what are gastric ulcers?
painful erosive lesions of the mucosa that may extend to deeper layers
what can cause gastric ulcers?
bacterial infections with H. pylori, effects of NSAIDS, overproduction of HCl or pepsin, and lowered production or secretion of mucus or bicarbonate
what are enteroendocrine cells?
scattered epithelial cells in the gastric mucosa with very distinct functions because they produce hormone products
what are most enteroendocrine cells?
APUD cells: they process amines
what are all of the enteroendocrine cells considered to be a part of?
the diffuse neuroendocrine system (DNES)
what are the two types of enteroendocrine cells?
closed type or open type
what are the closed type of enteroendocrine cells?
the cellular apex is covered by neighboring epithelial cells and they are not exposed to the GI lumen
what are the open type of enteroendocrine cells?
the apical end of the cell contacts the lumen and has chemoreceptors that sample luminal contents
what are the general characteristics of pyloric glands?
branched, coiled, tubular glands of the pylorus
what are pyloric glands lined by?
mucus-secreting cells with large and pale secretory mucus
what do the pyloric glands empty into?
into pits that occupy half of mucosa
what do the pyloric glands release?
gastrin from G cells
what can be seen in the lamina propria of the pylorus?
lymphoid nodules- GALT
