Histology Of The Stomach And Esophagus Flashcards
What three components does the mucosa of the GI tract generally contain?
Lining epithelium, underlying lamina propria (vascularized loose CT) with lymphatic nodules and WBC present, muscularis mucosa
What is muscularis mucosa?
A thin layer of smooth muscle that controls mobility and infoldings of the mucosa (does not participate in peristalsis)
What are general characteristics of submucosa?
Consists of dense irregular CT with neurovasculature and lymphatics
Glands may also be present (esophagus and duodenum)
What are some general characteristics of the muscularis externa?
Two layers of smooth muscle including an inner circular layer and an outer longitudinal layer
Neurovasculature plexuses reside between layers
Contraction of the inner circular layer of the muscularis externa causes what?
Construction of the gut lumen
Contraction of the longitudinal layer of the muscularis externa causes what?
Shortening of the GI tube
What is serosa?
Portion of the GI tract suspended by mesentery/peritoneum and covered by mesothelium
What is adventitia?
Areas of the GI tract without mesothelium covering it (retroperitoneal)
What are the 4 types of basic mucosa?
Protective, secretory, absorptive and absorptive/protective
Describe protective mucosa
Nonkeratinized stratified squamous epithelium
Found in oral cavity, pharynx and anal canal
Describe secretory mucosa
Simple columnar epithelium
Mucosa packed with glands
Found in stomach
Describe absorptive mucosa
Simple columnar epithelium
Mucosa arranged as villi with crypts
Glands may or may not be present (SI)
Describe absorptive/protective mucosa
Simple columnar epithelium
Mucosa closely packed
Glands with extensive goblet cells (LI)
Describe the esophagus
Fibromuscular tube that conveys food from oropharynx to stomach
Mucosal and Submucosa glands produce a thin layer of mucus to lubricate the epithelium
Cardiac esophageal glands reside in the lamina propria of terminal esophagus
Submucosal glands consist of small lobules with mucous and serous cell types
Describe the mucosa of the esophagus
Nonkeratinized stratified squamous epithelium overlying lamina propria
Numerous folds distend with food passage
Describe the submucosa of the esophagus
Network of collagen and elastic fibers with many small blood vessels
Submucosal venous plexuses drain into both the systemic and portal venous system (increased pressure can cause esophageal varices/dilation of submucosal venous sinuses)
The upper third esophagus has what type of muscle in the muscularis layer?
Skeletal muscle (striated)*
The middle of the esophagus has what type of muscle in the muscularis layer?
Skeletal and smooth*
The lower third of the esophagus has what type of muscle in the muscularis layer?
Smooth muscle*
What part of the esophagus contains adventitia?
Thoracic esophagus
What portion of the esophagus contains serosa?
Inferior to diaphragm
Describe the gastroesophageal junction
Epithelial transition from esophagus to stomach
Nonkeratinized stratified squamous —> simple columnar
Epithelium in the stomach is glandular with pits and glands
What are rugae?
Longitudinal folds of the gastric mucosa that expand during filling of the stomach
Covered by gastric pits
Gastric glands produce a mucosal barrier to protect mucosal surface
Describe the mucosa of the stomach
Simple columnar epithelium
Lamina propria contains cardiac, gastric and pyloric glands
Reticular and collagen fibers predominate
Muscularis mucosa facilitates release of gastric gland secretions
Describe the submucosa of the stomach
Dense irregular CT with collagen and elastic fibers
Arterioles, venous plexuses and lymphatics
Meissner’s plexus
Describe the muscularis of the stomach
Three layers of smooth muscle: oblique, circular and longitudinal
Circular muscle layer thickens in pyloric region forming the pyloric sphincter
What is the final layer of the stomach?
Serosa made of loose CT and blood vessels
What provides innervation to the stomach and esophagus?
Two plexuses of sensory and motor neurons linked by interneurons
Submucosal plexus of Meissner
Myenteric plexus of Auerbach which is between the inner circular and outer longitudinal layers of the muscularis externa
Preganglionic axons of parasympathetics increase or decrease motility?
Increases
Postganglionic axons of sympathetics increase or decrease motility?
Decrease
What is the action of the two plexuses innervating the stomach and esophagus?
Regulate and control peristaltic contractions of muscularis externa and movements of muscularis mucosa as well as secretory activities of the mucosal and submucosal glands
What is the lower esophageal sphincter?
A functional sphincter that prevents reflux of gastric contents
What is gastroesophageal reflux disease (GERD)?
Causes chronic inflammation, ulceration and difficulty swallowing (dysphagia) due to reflux of gastric contents
What is Barrett’s esophagus?
During chronic GERD conditions nonkeratinized stratified squamous epithelium in the transition zone becomes columnar mucus secreting/glandular epithelium resulting in Barretts
Describe fundic (gastric) glands
Simple branched tubular glands present throughout the gastric mucosa
Extend from bottom of gastric pits to muscularis mucosa
What is a gastric pit?
Invagination of the mucosal surface (part of fundic gland)
Describe the isthmus/neck of the fundic gland
Narrow region between the gastric pit and gastric gland (short and wide base)
Describe pyloric glands
Branched, coiled, tubular glands of the pylorus
Lined by mucous secreting cells with large and pale secretory mucus*
Glands empty into pits that occupy half of mucosa*
Largely release gastrin from G cells
Lymphoid nodules can be seen in the lamina propria (GALT)
Occasionally parietal cells are present
What are surface mucous cells?
Line the lumen and gastric pits (of fundic/gastric glands)
What are mucous neck cells?
Located in the neck in singles and/or clusters (in gastric/fundic gland)
Round nuclei and apical secretory granules
Describe mucous cells of the fundic/gastric glands
From a mucous layer containing 95% water and 5% mucin
Forms an insoluble gel that attaches to the surface of gastric mucosa
Thick coating that neutralizes the microenvironment to an alkaline pH
Where are chief cells found?
In clusters in the inferior 1/3 of gastric glands
What are the hallmarks of chief cells?*
Abundant RER and apical secretory (zymogen) granules
Basal nuclei with basophilic cytoplasm
What do chief (zymogenic) cells secrete?
Pepsinogen and gastric lipase (which digests lipids)
What is 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
What do parietal cells produce?
HCl and intrinsic factor (a glycoprotein that binds to vitamin B12)
Describe parietal cells
Predominate near the neck and upper segments of the gastric gland
Active parietal cells have a deep invagination of the apical plasma membrane known as an intracellular canaliculus (large surface area produced by 1000s of microvilli)
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
Describe enteroendocrine cells
Scattered epithelial cells in the gastric mucosa named with the initial letter of their main hormone product (important for digestive function)
Most are APUD cells and process amines (amine precursor uptake and decarboxylation activity)
All generally considered part of the diffuse neuroendocrine system (DNES)
Release products that exert paracrine or endocrine effects
What is a closed enteroendocrine cell?
Cellular apex i is covered by neighboring epithelial cells
Not exposed to GI lumen
What is an open enteroendocrine cell?
Apical end of the cell contacts the lumen and has chemoreceptors that sample luminal contents
What are the effects of the hormones released by enteroendocrine cells?
Regulation of peristalsis and motility
Secretion of digestive enzymes, water and electrolytes
Sense of being satiated after eating
What are gastric ulcers?
Painful erosive lesions of the mucosa that may extend to deeper layers
Can occur anywhere between the lower esophagus and portions of the SI
What are the causes of gastric ulcers?
Infections with H pylori, effects of NSAIDs, overproduction of HCl or pepsin, and lowered production or secretion of mucous or bicarbonate
