Digestive System Histology Flashcards
Basic structure of GI
mucosa, submucosa, muscularis externa, serosa/adventitia
mucosa components
epithelium, lamina propria, muscularis mucosa
submucosa
connective tissue usually more dense than mucosa, larger blood vessels, nerve plexes, glands, lymphatic nodules
lamina propria
vascularized connective tissue deep to epithelium
what types of immune cells in mucosa
lymphocytes, plasma cells, macrophages
Serosa
outer covering of epithelial cells separated from muscularis by thin connective tissue; called adventitia in esophagus above diaphragm where outer squamous layer absent
Esophagus purpose
pass food from pharynx to stomach; no digestive function
Esophagus epithelial cells
non-cornified squamous epithelium
muscle in esophagus
upper part – skeletal
lower 1/3 - solely smooth
middle = mix
LES
lower esophageal sphincter
- not true sphincter but incomplete sphincter maintain contraction to prevent reflux
stomach regions
cardia= small area of mucus-secreting glands around esophageal entry fundus= main body secreting acid, peptic digestive products, and mucus pyloris = secretes mainly mucus and relative preponderance of endocrine cells secreting gastrin
what is different about stomach
- rugae/plicae mucosa= longitudinal folds that disappear upon distention
- mucosal structure
- third oblique layer of smooth muscle just lumenally to circular mucosal layer
how is stomach mucosal structure different
mucous secreting cells arranged in folds separated by gastric pits that secrete mucous
- pit epithelium changes and continues deep into mucosa as 1 or more gastric glands
where are gastric stem cells
in upper neck region of gastric pit epithlium; they divide and rise upward to mucous secreting cells or downward to specialized cells in gastric glands
surface mucous cells
release vesicles of stomach mucins/bicarb to coat surface; glycocalyx covers microvilli
chief cells in stomach
protein secretors with apical granules and elaborate RER
- mainly secrete pepsinogen, which is converted to pepsin in presence of acid
parietal cells in stomach
- acid-producing cells that pump H into lumen against steep gradient
- also secrete intrinsic factor, important in B12 uptake and for RBC production
- microvilli bordering canaliculi– enormous SA for pumping
- lots of mitochondria
- stimulated to produce acid by gastrin and histamine
Zollinger-Ellison syndrome
excessive gastrin secretion –> too much HCl by parietal cells that can’t be correctly neutralized, leading to ulcers induodenal
Enteroendocrine cells of stomach
A cells, G cells, serotonin-secreting EC cells, somatostatin D- cells
A cells
secrete glucagon; stomach and SI
Dcells
stomach, SI, LI; secrete somatostatin
EC cells
stomach, SI, LI; secrete serotonin, substance P
ECL cells
stomach; release histamine to stimulate HCL secretion
G cells
Stomach/SI; secrete gastrin