Histology of Esophagus & Stomach (Dennis) Flashcards
What are the 4 layers of the GI tract from lumen to superficial?
- mucosa (epithelium, lamina propria, muscularis mucosae)
- submucosa (dense irregular CT, glands, neurovasculature)
- muscularis externa (inner circular layer, myenteric nerve plexus, outer longitudinal layer)
- serosa/adventitia (covered by peritoneum, retroperitoneal)
(mucosa differs from region to region reflecting function, other layers have less variation w/ subtle differences)
- GI layer w/ 3 compartments
- lining epithelium varies segment to segment
- lamina propria (vascularized loose CT) w/ lymphatic nodules and WBC present
- muscularis mucosae thin layer of smooth muscle that controls mobility and infoldings of mucosa
mucosa
- GI layer comprised of dense irregular CT w/ neurovasculature and lymphatics
- glands may be present (esophagus and duodenum)
submucosa
- GI layer that is 2 layers of smooth muscle, and inner circular layer, and outer longitudinal layer
- contraction of circular layer constricts lumen
- contraction of longitudinal layer shortens the tube
- neurovascular plexuses reside between layers
muscularis/muscularis externa layer
What is the difference between serosa vs adventitia in the GI tract?
- serosa and adventitia make up the outer layer of the GI tract
- in parts of the GI tract that are suspended by mesentery/peritoneal fold, the adventitia is covered by mesothelium and forms a serosa layer
- in parts of the GI track without mesothelium covering, there is just adventitia
- serosa covers organs that freely move inside a cavity (intraperitoneal organs)
- adventitia covers the organs that should be bound with the surrounding structures for support (retroperitoneal organs)
Name the following GI layers:
Name the following GI layers:
- type of basic mucosa
- nonkeratinized stratified squamous
- found in oral cavity, pharynx, and anal canal
protective
- type of basic mucosa
- simple columnar epithelium
- mucosa packed w/ glands, found in stomach
secretory
- type of basic mucosa
- simple columnar epithelium
- mucosa arranged as villi w/ crypts, glands may or may not be present (SI)
absorptive
- type of basic mucosa
- simple columnar epithelium
- mucosa arranged into closely packed glands w/ extensive goblet cells (LI)
absorptive/protective
What is the physiology and function of intrinsic (enteric) innervation?
two plexuses of sensory and motor neurons, linked by interneurons:
1) submucosal plexus of Meissner
2) myenteric plexus of Auerbach (between the inner circular and outer longitudinal layers of muscularis layer)
function
reponsive to local stimuli and input from ANS to regulate and control:
1) peristaltic contractions of muscularis externa and movements of mucularis mucosae
2) secretory activities of the mucosal and submucosal glands
preganglionic axons of the parasympathetics (increase motility)
postganglionic axons of sympathetics (decrease motility)
- fibromuscular tube that conveys food from oropharynx to stomach
- both serosa and adventitia tissue: thoracic part = adventitia; inferior to diaphragm = serosa
- mucosal and submucosal glands prod thin layer of mucus to lubricate epithelium
esophagus
Describe the mucosal layer of the esophagus:
- mucosal and submucosal glands prod thin layer of mucus to lubricate epithelium
- cardiac esophageal glands: reside in lamina propria of terminal esophagus
- submucosal glands: consist of small lobules w/ mucous and serous cell types
- mucosa: nonkeratinized stratified squamous overlying a lamina propria; numerous folds distend w/ food passage
Describe the submucosa of the esophagus:
- network of collagen and elastic fibers, many small blood vessels
- submucosal venus plexus drain into both systemic and portal venous system
- increased pressure can cause esophageal varices, dilation of the submucosal venous sinuses
Describe the muscularis layer of the esophagus:
- inner circular and outer longitudinal layers have segment-dependent variations
- upper third: skeletal muscle (striated)
- middle third: skeletal and smooth
- lower third: smooth muscle
- condition that causes chronic inflammation, ulceration, and dysphagia due to reflux of gastric contents
- lower esophageal sphincter: functional sphincter that usually prevents reflux of gastric contents
GERD
condition that occurs when chronic, nonkeratinized stratified squamous epithelium in transition zone of esophagus becomes columnar mucus secreting/glandular
Barrett’s esophagus
- epithelial transition from esophagus to stomach
- nonkeratinized stratified squamous epithelium > simple columnar epithelium in the stomach (glandular w/ pits and glands)
gastroesophageal junction
What are the regions and important structures of the stomach?
4 regions:
- cardia: 2-3 cm near esophageal opening
- fundus: projects to the left of the cardiac
- body: extensive central region
- pyloris: ends at gastroduodenal orifice
structures:
- rugae: longitudinal folds of the gastric mucosa that expand during filling of stomach
- rugae are covered by gastric pits
- gastric glands: prod 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 mucosae facilitates release of gastric gland secretions
Describe the submucosa of the stomach:
- dense irregular CT w/ collagen and elastic fibers
- arterioles, venous plexuses, and lymphatics
- Meissner’s plexus
Describe the muscularis externa and serosa layers of the stomach:
- muscularis: 3 layers of smooth muscle: oblique, circular, and longitudinal (poorly defined); circular muscle layer thickens in pyloric region, forming pyloric sphincter
- serosa: loose CT and blood vessels
Where are fundic (gastric) glands located and what is the general structure of these glands?
- fundic glands: simple, branched, tubular glands present throughout gastric mucosa; extend from bottom of gastric pits > muscularis mucosae
- gastric pit: invaginations of the mucosal surface
- isthmus/neck: narrow region between gastric pit and gastric gland
- gastric gland: shorter and wider base
What cells types are present within gastric pits and gastric glands?
(from top of gastric pit to bottom of gastric gland)
- surface mucous cells: secrete alkaline fluid containing mucin
- mucous neck cells: secrete acidic fluid containing mucin
- parietal cells: secrete intrinsic factor and HCL
- chief cells: secrete pepsinogen and gastric lipase
- G cells: enteroendocrine cells that secrete gastrin into blood
Name the following structures within gastric glands:
Name the following structures within gastric glands:
Name the following structures within gastric glands:
Name the following cell types within gastric glands:
- GP: gastric pits
- MM: muscularis mucosae
- SM: surface mucous
- NM: mucous neck
- P: parietal cells
- C: chief cells
What are the different types of mucous cells within the stomach and what are their functions?
- surface mucous cells: line the lumen and gastric pits
- mucous neck cells: located in the neck in singles and/or clusters; have round nuclei and apical secretory granules
functions:
- surface cells: secrete alkaline fluid containing mucin
- neck cells: secrete acidic fluid containing mucin
- produce a mucous layer, containing 95% water and 5% mucin
- forms an insoluble gel that attaches to surface of gastric mucosa
- thick coating that neutralizes the microenvironment to an alkaline pH
What is the location/structure of chief (zymogenic) cells within the stomach and what is their function?
- location: found in clusters in inferior 1/3 of gastric glands
- structure: abundant in RER and apical secretory (zymogen) granules; basal nuclei w/ basophilic cytoplasm
function:
- release pepsinogen, a proenzyme stored in secretory granules, that is released/converted into pepsin by acidic environment
- pepsin is a proteolytic enzyme that digests most proteins
- exocytosis of pepsinogen is rapid and stimulated by feeding
- chief cells also prod gastric lipase, which digests lipids
What is the locatin/structure of parietal cells within the stomach and what is their function?
- location: predominate near neck and upper segment of gastric gland
- structure: large cells, usually round or pyramidal shaped; one (sometimes two) central round nucleus; cytoplasm is eosinophilic due to inc mito content
function:
- prod hydrochloric acid (of gastric juice) and intrinsic factor, a glycoprotein that binds to vit B12
- active parietal cells have deep invagination of apical plasma membrane, an intracellular canaliculus, that creates a large surface area prod by thousands of microvilli
- scattered epithelial cells in the gastric mucosa, named w/ the initial letter of their main hormone prod
- different hormones are of major importance for digestive function
- most are APUD cells, process amines: “amine precursor uptake and decarboxylation” activity
- all generally considered part of the diffuse neuroendocrine system (DNES)
enteroendocrine cells
image:
- CCK: cholecystokinin
- VIP: vasoactive intestinal peptide
- GIP: gastric inhibitory peptide
What is the function of enteroendocrine cells, the different types, and the hormonal effects?
- function: release prod that exert paracrine or endocrine effects
types:
- “closed” type: cellular apex is covered by neighboring epithelial cells, not exposed to GI lumen
- “open” type: apical end of the cell contacts the lumen and has chemoreceptors that sample luminal contents
hormonal effects:
- regulation of peristalsis and motility
- secretion of digestive enzymes, water, and electrolytes
- sense of satiation after eating
- branched, coiled, tubular glands of the pylorus
- lined by mucus-secreting cells w/ large and pale secretory mucus
- glands empty into pits that occupy half of mucosa
- largely release gastrin from G cells
- occasional parietal cells are present
- lymphoid nodules can be seen in the lamina propria (GALT - gut associated lymphoid tissue)
pyloric glands
Identify the area within the body this is taken from and the highlighted structures:
Identify the area within the body this is taken from and the highlighted structures:
Identify the area within the body this is taken from and the highlighted structures:
Identify the area within the body this is taken from and the highlighted structures:
Identify the area within the body this is taken from and the highlighted structures:
Identify the area within the body this is taken from and the highlighted structures:
Identify the area within the body this is taken from and the highlighted structures:
Identify the area within the body this is taken from and the highlighted structures:
