Histology of the esophagus and the stomach Flashcards
what are the four main layers of the GI tract?
from lumen to superficial:
1) The mucosa
2) the submucosa
3) the muscularis externa
4) the serosa/adventitia
Components of the general Mucosal layer
Has three components:
-lining epithelium (varies segment to segment)
-underlying lamina propria (vascularized loose CT) lymphatic nodules, lymphocytes, plasma cells, and macrophages are present here
-A thin layer of smooth muscle, the muscularis mucosae
which controls the mobility of the mucosa glands
Components of the general submucosal layer
Submucosal layer is composed of
- consists of a dense irregular CT with neurovascular and lymphatics
- glands may also be present in the esophagus and duodenum
Components of the general Muscularis externa layer
Two layers of smooth muscle, inner circular layer and a outer longitudinal layer
contraction of circular will constrict lumen
contraction of the longitudinal layer will shorten the lumen
Neurovascular plexuses reside between layers
Components of the general Serosa/Adventitia layer
When digestive tube is suspended by a mesentary/peritoneal fold, the adventita is covered by mesothelium forming the serosa layer (peritoneum)
those without mesothelium covering have an adventita (retroperitoneal)
organs may have an adventita and or serosa depending on the location
what are the 4 basic mucosal types, where they are found and their function in the GI tract
Nonkeratinized stratified squamous cells:
- found in oral cavity, pharynx, and anal canal
- protective
Simple columnar epithelium:
- mucosa arranged as villi with crypts, glands and maybe present in small intestine
- absorptive
Simple columnar epithelium
- mucosa packed with glands
- found in stomach
- secretory
Simple columnar epithelium
- mucosa arranged into closely packed glands with extensive goblet cells
- found in large intestine
- Absorptive and protective
what are the two plexuses found in the epithelium and their function
Part of the intrinsic (enteric) innervation
1) submucosal plexus of meissner
2) myenteric plexus of auerbach
- between the inner circular and outer longitudinal layers
Responsive to local stimuli and input from the ANS regulate control:
- peristalic contractions of muscularis externa and movements of the muscularis mucosae
- secretory activities of the mucosal and submucosal glands
does the esophagus have serosa or adventita?
both:
Thoracic esophagus is adventita because it is retroperitoneal
inferior to the diaphram is serosa because it is peritoneal
Characteristics of the Mucosa, Submucosa and muscularis layers of the esophagus
Mucosa:
- nonkeratinized stratified squamous overlying a lamina propria
- numerous folds
- muscularis mucosae only found in lower segment
submucosa:
- network of collagen, elastic fibers and small blood vessels
- Submucosal venous plexuses drain both the systemic and portal venous systems
- increase in pressure can cause esophageal varices
Muscularis:
- inner circular and outer longitudinal layers have segment dependent variations
- upper third = skeletal muscle
- middle third = skeletal and smooth muscle
- lower third = smooth muscle
what are two glands found in the esophagus and their function
Mucosal and submucosal produce a thin layer of mucus to lubricate the epithelium
- Cardiac esophageal glands: reside in the lamina propria of termial esophagus and help protect from acids from the stomach
- Submucosal glands: consist of small lobules with mucous and serous cell types drained by a single duct
what are the sphincters of the esophagus?
Upper esophageal sphincter (UES)
-anatomical. swallowing reflex
Lower esophageal sphincter (LES)
-functional, prevents reflux of gastric contents
what is GERD and Barretts esophagus
Gastroesophageal reflux disease:
-causes chronic inflammation, ulceration and difficult in swallowing (dysphagia) due to reflux of gastric contents
If chronic, nonkeratinized stratified squamous in transition to columnar mucus secreting glandular that is similar to the stomach cell type
-this dysplasia is called barretts esophagus
What is the gastroesophageal junction?
Epithelial transition from the esophagus to the stomach
- nonkeratinized stratified squamous to simple columnar
- epithelium in the stomach is glandular with pits and glands
what are the 4 regions and 2 motillity areas of the stomach
Four regions:
- Cardia: near the esophageal opening
- fundus, projects to the left of the cardia
- body, an extensive central region
- Pyloric antrum: ends at the gastroduodenal orifice
Based on motillity characteristics:
- Orad area = fundus, and upper part of the body relaxes during swallowing
- caudad area: lower portion of the body and the antrum that participates in the regulation of gastric emptying
what are rugae?
Gastric mucosal folds that are covered by gastric pits
this is also covered by a gastric mucosal barrier that protects the mucosal surface
Mucosa, submucosa, muscularis, and serosa of the stomach
Mucosa:
- simple columnar epithelium
- lamina proprioa contains cardiac, gastric, and pyloric glands
- reticular and collagen fibers predominate
- muscularis mucosae facillitates release of gastric gland secretions
submucosa:
- dense irregular CT w collagen and elastic fibers
- arterioles, venous plexuses and lymphatics
- meissners plexus (submucosal plexus)
Muscularis externa
- three layers of smoot muscle, oblique, circular, and longitudingal
- circular muscle layer thickens in pyloric region forming the pyloric sphincter
Serosa:
-loose CT and blood vessels
what are the fundic glands and what make up its components?
Simple branched tubular glands that are present throughout the gastric mucosa
-extend from the bottom of the gastric pit to the muscularis mucosae
Gastric pit:
-invaginations of the mucosal surface
Isthmus/neck:
- narrow region between gastric pit and gastric gland
- contain stem cells
Gastric gland:
-shorter and wider base
what are the characteristics of the 2 mucous cells? what do they secrete
Surface mucous cells that line the lumen and the gastric pit
Mucous neck cells that are located in the neck in singles and or clusters
- round nuclei and apical secretory granules
- also down into the gastric gland
these secrete a mucus layer that contains 95% water and 5% mucin
- forms an insoluble gel that attaches to the surface of the gastric mucosa
- thick coating that neutralizes the micronenvironment to an alkaline pH
what are chief cells and their function
Predominately in inferior regions of the gastric glands
-abundant RER and apical secretory zymogen granules
produce Pepsinogen, the proenzyme stored in secretory granules
- released and converted to pepsin by acidic environment
- proteolytic enzyme that digests most proteins
- exocytosis of pepsinogen is rapid and stimulated by feeding
also produce gastric lipase to digest lipids
what are Parietal cells and their function
Predominate near neck and upper segment of the gastric gland
Produce HCl acid and intrinsic factor which is a glycoproptein that binds vitamin B12
Large cells usually round or pyramidal shaped
- one or two central round nuclei
- cytoplasm is esentially eosinophillic due high amounts of mitochondria
contain an intracellular canaliculus
-large surface area produced by thousands of microvili
what are enteroendocrine cells and their function?
Scattered epithelial cells in gastric mucosa with endocrine/paracrine functions
secrete a range of products physiological critical for digestive function
important for releasing hormones and are found throughout the GI tract
What are cardiac glands and their function?
Found in the narrow region of the stomach (cardia) that surrounds the esophageal orifice
glands are tubular, coiled and somewhat branched
opening is continuous with the gastric pits
lined with mucus secreting cells
appear circular and oblique in sections
what are pyloric glands and what are their functions
Branched coiled tubular glands between fundus and pylorus
glands empty into pits that occupy half of mucosa
lined by mucus secreting cells
-large pale secretory mucus
Occasional enteroendocrine cells and parietal cells are present
lymphoid nodules can be seen in the lamina propria (GALT)
