Histology of the Esophagus and Stomach Flashcards
Organization of the GI tract
mucosa
submucosa
muscularis externa
serosa/adventitia
Mucosal Layer
Three components!
- lining epithelium (varies segment to segment)
- underlying lamina propria (vascularized loose CT has lymphatic nodules, lymphocytes, plasma cells, macrophages)
- muscularis mucosae (this smooth m) –> controls mobility of mucosa/mucosal glands
submucosal layer
- dense irregular CT w/ neurovasculature and lymphatics
- glands may also be present (esophagus/duodenum)
Muscularis Externa
two layers of smooth muscle (inner circular/outer longitudinal)
-contraction of circular =constricts lumen
-contraction of longitudinal=shortens tube
neurovascular plexuses reside between layers
Serosa/Adventitia
When digested tube is suspended by a mesentery/periotneal fold= covered by mesothelium=serosa
-no mesothelium?=adventitia
you can have either or/or both!
GI innervation
extrinsic-para and symp
intrinsic=enteric
Parasympathetics of GI
vagus nerve (until splenic fixure) pelvic splanchnic (splenic flexure --> inferiorly fibers in vagus and pelvic splanchnics are presynaptic ganglion and post synaptic fibers are intramural
Sympathetics of 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
Intrinsic Innvervation
two plexuses of sensory and motor linked by interneurons
1) submucosal plexus of meissner-found in submucosa and is responsible for regulating secretion of glands in submucosa
2) myenteric plexus of auerbach-between inner circ and outer long. layers (lighter stained)
Myenteria/Meissner
responsive to local stimuli and input from ANS
regulate and control:
1)peristaltic contractions of muscularis externa and movements of muscularis mucosae
2) secretory activities of the mucosal and submucosal glands
Esophagus
fibromuscular tube that conveys food from oropharynx to stomach
thoracic eso: adventitia
inferior to diaphragm=serosa
TWO GLANDS: cardiac/submucosal
Cardiac Esophageal glands
produce a thin layer of mucus to lubricate the epi.
reside in the lamina propria of terminal esophagus
submucosal glands
produce a thin layer of mucus to lubricate the epi.
consists of small lobules with mucous and serous cell types, drained by a single duct
Gastroesophageal junction
epithelial transition from esophagus to stomach
nonkeratinized stratified squamous –> simple columnar
epi. in the stomach is glandular, with pits and glands
Sphincters of Esophagus
Upper esophageal sphincter: anatomical, swallowing reflex
lower esophageal sphincter: functional, prevents reflex of gastric contents (designed to be closed down so acid components dont move superiorly)
Gastroesophageal reflux disease (GERD)
causes chronic inflammation, ulceration, and difficulty swallowing (dysphagia) due to reflex of gastric contents
-loosening of sphincter causes backflow of acid
Barret’s Esophagus
chronic
nonkeratinized stratified squamous in transition zone –> becomes columnar mucus-secreting/glandular, barret’s esophagus/metaplasia
Regions of stomach
cardia: 2-3 cm near esophageal opening
fundus: projects to the left of the cardia
body: extensive central region
pyloric antrum: ends at gastroduodenal orifice
Orad area
fundus and upper part of the body, relaxes during swallowing
LES area
caudad area
lower portion of the body and the antrum, participates in the regulation of gastric emptying
Rugae
gastric mucosal folds/ridges that mix food and break it down. IT helps to increase friction and break down internal food components.
in mucosa/submucosa
-covered by gastric pits
Fundic (gastric) glands
present throughout gastric mucosa except for areas occupied by cardiac and pyloric glands
-simple branched tubular glands (extend from bottom of gastric pits –> muscularis muscosae) (several open into a single gastric pit)
Gastric gland: isthmus
between gastric pit and gland below
site of stem cell niche
-dividing and undifferentiated cells (connector region of functional component of gland to gastric pit)
gastric gland: neck segment
narrow, relatively long region
mucous neck cells (secrete mucus)
parietal cells
enteroendocrine cells
gastric gland: fundic segment
shorter and wider base
-chief cells
-enteroendocrine cells
some parietal cells
Mucous cells
a mucus layer, containing 95% water, 5% mucin
- forms an insoluble gel that attaches to surface of gastric mucosa
- 100 um thick coating that neutralizes the microenvironment to an alkaline pH
surface mucous cells
line the pits (insoluble)
have apical granules containing mucins.
has abundant mito, and carbonic anhydrase contribute to the formation of bicarbonate ions –> increase pH
mucous neck cells
located in the neck, at the opening of the gastric gland into the pit
Chief cells
basal region of the cytoplasms contains extensive RER
numerous zymogen granules are located in apical region. release contents via exocytosis
Pepsinogen
proenzyme stored in the zymogen granules
- released into the lumen of the gland
- converted to pepsin by acid enviroment
- proteolytic enzyme that digests most proteins
- exocytosis of pepsinogen is rapid and simulated by feeding
Enteroendocrine cells
have two types of cells: closed cells and open cells
-all levels of fundic glands, but more prevalent in the base
Closed cells of 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
Open cells of enteroendocrine cells
have a thin cytoplasmic extension w/ microvilli and are exposed to gland lumen
-chemoreceptors that sample luminal contents and release hormones
Gastrin
produced by G cells in pyloric antrum
- stimulates production of HCL by parietal cells
- released in stomach, duodenum, jejunum
somatostatin
produced by D cells
- inhibits gastrin action
- throughout entire GI tract
ghrelin
produced in gastric fundus
-binds its receptor in pituitary and stimulates GH secretion
-Ghrelin plasma levels increase during fasting –> triggers hunger
released in fundus
Cardiac Glands of Stomach
narrow region of stomach (the 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
Hallmark: appear circular and oblique in sections
Pyloric Glands of stomach
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
occasional enteroendocrine cells and parietal cells are present; GALT in lamina propria
