Histology of Esophagus and Stomach Flashcards
What are the four layers of the GI tract (lumen to superficial)?
- the mucosa
- the submucosa
- the muscularis externa
- the serosa/adventitia
What layer of the GI tract differs considerably from region to region?
mucosa - reflects functional activity
What is the serosa covered by?
peritoneum
Where is adventitia?
retroperitoneal
What are the 3 components of the mucosal layer?
- lining epithelium (varies by segment)
- underlying lamina propria (vascularized loose CT)
- a thin layer of smooth muscle called muscularis mucosae
Where are the lymphatic nodules, lymphocytes, plasma cells, and macrophages?
the lamina propria of the mucosal layer of the GI tract
What is the function of the muscularis mucosae?
controls mobility of mucosa/mucosal glands
What is the submucosal layer comprised of?
- dense irregular CT with neurovasculature and lymphatics
- glands may be present (esophagus and duodenum)
What makes up the muscularis externa?
two layers of smooth muscle
- inner circular layer
- outer longitudinal layer
What happens when the circular layer of the muscularis externa contracts?
constriction of the lumen
What happens when the longitudinal layer of the muscularis externa contracts?
shortens the tube
Where do neurovascular plexuses reside in the muscularis externa?
between layers
What is the serosa?
the adventitia covered by mesothelium when digestive tube is suspended by a mesentery/peritoneal fold
Is adventitia covered by mesothelium?
No, if it is covered by mesothelium it is called serosa
What determines if organs have adventitia or serosa?
depends on location
- if it has mesothelium it is serosa
- if no mesothelium, it is adventitia
What is the digestive tube innervated by?
extrinsic component and intrinsic component
What is the extrinsic component?
parasympathetics and sympathetics
What is the intrinsic component
enteric
What parasympathetics innervate GI?
- vagus nerve (presynaptic) until splenic flexure
- pelvic splanchnics (presynaptic) from splenic flexure inferiorly
- ganglion and postsynaptic fibers are intermural
What sympathetics innervate GI?
- branches from greater, lesser, least, and lumbar splanchnics
- synapse in prevertebral ganglia (celiac, SM, aorticorenal, and IM ganglia)
- postsynaptic nerves travel to organs via blood vessels on peri-arterial plexuses
What are the plexuses of sensory and motor neurons in the intrinsic innervation of GI?
- submucosal plexus of Meissner
2. Myenteric plexus of Auerbach
Where is the myenteric plexus of Auerbach?
between the inner circular and outer longitudinal layers (muscularis externa)
What is the intrinsic innervation responsive to?
local stimuli and input from ANS
What does the intrinsic innervation regulate and control?
- peristaltic contractions of muscularis externa and movements of muscularis mucosae
- secretory activities of the mucosal and submucosal glands
Do these increase or decrease GI motility?
- preganglionic axons of parasympathetics
- postganglionic axons of sympathetics
- increase
2. decrease
What is the esophagus?
fibromuscular tube that conveys food from oropharynx to stomach
Does the esophagus have serosa or adventitia?
both
Where is adventitia of the esophagus?
thoracic esophagus
Where is the serosa of the esophagus?
inferior to diaphragm
What do mucosal and submucosal glands produce?
a thin layer of mucus to lubricate the epithelium
Where do cardiac esophageal glands reside?
in the lamina propria of terminal esophagus
Describe submucosal glands
small lobules with mucous and serous cell types, drained by a single duct
Describe the mucosa layer of the esophagus
- nonkeratinized stratified squamous overlying a lamina propria
- numerous folds
- muscularis muscosae is only present in lower segment
Describe the submucosa of the esophagus
- network of collagen and elastic fibers, many small blood vessels
- submucosal venous plexuses drain into both the systemic and portal venous system
What causes esophageal varicies?
Where?
What are esophageal varicies?
- caused by increased pressure
- submucosa of esophagus
- dilation of the submucosal venous sinuses
Describe the muscularis in general, upper, middle, and lower thirds
- inner circular and outer longitudinal layers have segment dependent variations
- upper third = skeletal muscle (striated)
- middle third = skeletal and smooth
- lower third = smooth muscle
What is the gastroesophageal junction?
epithelial transition from esophagus to stomach:
nonkeratinized stratified squamous to simple columnar
Is epithelium in the stomach glandular?
Yes, epithelium in the stomach is glandular, with pits and glands
What are the sphincters of the esophagus?
upper esophageal sphincter (UES)
lower esophageal sphincter (LES)
Is the UES anatomical or functional? What does it do?
anatomical
swallowing reflex
Is the LES anatomical or functional? What does it do?
functional
prevents reflux of gastric contents
What is GERD?
gastroesophageal reflux disease
- causes chronic inflammation, ulceration, and difficulty in swallowing (dysphagia) due to reflux of gastric contents
What is the medical term for difficulty swallowing?
dysphagia
What is Barrett’s esophagus/metplasia?
chronic GERD
- nonkeratinized stratified squamous in transition zone becomes columnar muscus-secreting/glandular
What are the four regions of the stomach? Describe location of each.
cardia - 2-3 cm near esophageal opening
fundus - projects to the left of the cardia
body - an extensive central region
pyloric antrum - ends at gastroduodenal orifice
What is the orad area of the stomach?
fundus and upper part of body that relaxes during swallowing
What is the caudad area of the stomach?
lower portion of the body and the antrum, participates int eh regulation of gastric emptying
What protects the mucosal surface?
a gastric mucosal barrier
What are gastric mucosal folds called? What are they covered by?
- called rugae
- covered by gastric pits
Describe the mucosa of the stomach
- simple columnar epithelium
- lamina propria contains cardiac, gastric, and pyloric glands
- reticular and collagen fibers predominate
- muscularis mucosae facilitates release of gastric gland secretions
What fibers are predominate in the mucosa of the stomach?
reticular and collagen fibers
What facilitates release of gastric gland secretions in the stomach?
muscularis mucosae
What types of glands are in the lamina propria of the stomach?
cardiac, gastric, and pyloric glands
What epithelium does the mucosa of the stomach have?
simple columnar epithelium
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/muscularis externa of the stomach
-3 layers of smooth muscle: oblique, circular, and longitudinal
What forms the pyloric sphincter?
circular muscle layer thickening in pyloric region in the muscularis/muscularis externa of the stomach
Describe the serosa of the stomach
loose CT and blood vessels
Does the stomach have serosa or adventitia?
serosa
Where are the fundic (gastric) glands?
present throughout gastric mucosa except for areas occupied by cardiac and pyloric glands
Describe fundic (gastric) glands
simple, branched, tubular glands
- extend from bottom of gastric pits to muscularis mucosae
- several open into a single gastric pit
What are the 3 regions of fundic (gastric) glands?
- isthmus - between gastric pit and gland below; site of stem cell niche
- neck segment - narrow, relatively long region
- fundic segment - shorter and wider base
What kind of cells are in the gastric pit, isthmus, neck, and fundus?
gastric pit: surface mucous cells
isthmus: dividing and undifferentiated cells
neck: mucous neck cells, parietal cells, enteroendocrine cells
fundus: chief cells, enteroendocrine cells, some parietal cells
What do surface mucous cells secrete?
alkaline fluid containing mucin
What do mucous neck cells secrete?
acidic fluid containing mucin
What do parietal cells secrete?
intrinsic factor and hydrochloric acid
What do chief cells secrete?
pepsinogen and gastric lipase
What do G cells secrete?
gastrin into the blood
Where are surface mucous cells?
line the pits
Where are mucous neck cells?
located in the neck at the opening of the gastric gland into the pit
What is the mucus layer in mucous cells?
95% water, 5% mucin
- forms an insoluble gel that attaches to surface of gastric mucosa
- 100 micrometer thick coating that neutralizes the microenvironment to an alkaline pH
Where are chief cells located?
basal region of the cytoplasm containing extensive RER
What type of granules are in chief cells? Where?
zymogen granules
apical region
What is pepsinogen?
the proenzyme stored in zymogen granules
- released into the lumen of gland
- converted to pepsin by acid environment
- proteolytic enzyme that digests most proteins
- exocytosis of pepsinogen is rapid and stimulated by feeding
Describe parietal cells:
- location
- what they produce
- predominate near neck and upper segment of the gastric gland
- produce hydrochloric acid (of gastric juice) and intrinsic factor (a glycoprotein that binds to vitamin B12)
What are three distinctive features of parietal cells?
- abundant mitochondria - produce ATP to pump H+ into secretory canaliculus
- intracellular canaliculus - an invagination of the apical surface and continuous with the lumen of gastric gland
- an H+, K+ dependent ATPase rich tubulovesicular system - distributed along the secretory canaliculus during the resting state
Describe enteroendocrine cell location
all levels of fundic glands, but more prevalent in the base
What are closed cells?
enteroendocrine cells: small cells that rest on the basal lamina and do not always reach the lumen
- indirectly regulated by luminal content via neural and paracrine mechanisms
What are open cells?
enteroendocrine cells: have a thin cytoplasmic extension with microvilli and are exposed to gland lumen
-chemoreceptors that sample luminal content and release hormones
What enteroendocrine cells are chemoreceptors that release hormones?
open cells
What produces gastrin? Where?
What does gastrin stimulate?
produced by G cells in pyloric antrum
stimulates production of HCl by parietal cells
What produces somatostatin? What is its function?
produced by D cells
inhibits gastrin action
What produces ghrelin? What is its function?
produced in gastric fundus
- binds its receptor in pituitary and stimulates GH secretion
- Ghrelin plasma levels increase during fasting to stimulate hunger
Describe cardiac glands
- narrow region of stomach (the cardia) that surrounds esophageal orifice
- glands are tubular, coiled, and somewhat branched
- opening is continuous with the gastric pits
- lined with mucus secreting cells (similar to esophagus)
What is the hallmark of cardiac glands?
appear circular and oblique in sections
Describe pyloric glands
- branched, coiled, tubular glands between fundus and pylorus
- glands empty into pits that occupy half of mucosa
- lined by mucus-secreting cells (resemble surface mucous cells)
- large and pale secretory mucus
What is GALT?
lymphoid notules seen in the lamina propria
