histology of upper GIT ( W1) Flashcards
what is the basic structure of digestive tract ?
Hollow tube of varying diameter
wall made up of 4 layers :
Mucosa ( inner )
submucosa
muscularis externa
serosa/adventita
what is the mucosa epithelial lining of the esophagus?
stratified squamous NON KERATINIZED epithelium
what is the mucosa epithelial lining of the stomach to the colon?
Simple columnar
what is the mucosa epithelial lining of the anal canal and rectum?
Stratified squamous KERTINIZED
what is the content of lamina propria of the mucosa?
Collagen
Reticular fibers
Blood vessels
nerve ending
glands
Mucosa associated lymph tissue ( MALT)—> monitor and produce an immune response to pathogens passing with food through GI tract
what is the contents of muscularis mucosa MM?
Very thin smooth muscle which cause local folding of the mucosal layer
Inner —> circular
Outer —> longitudinal
it extends to the mucosa but not villi ( it stays behind the mucosa )
when is the outermost layer serosa and when it is adventitia ?
if organ is intra - peritoneal —> serosa ( simple squamous ) like transverse colon
If organ is retroperitoneal —> adventitia ( loose connective tissue and nerves ) like ascending and descending colon
what is the order of organization of plica/villi/microvilli in small intestine ?
one pilca circularis has many villi projecting from it
the villi is covered by columnar cells
columnar cells has projections called microvilli
what is the content of submucosa?
loose areolar connective tissue
Elastic fibers
blood vessels
lymphatic vessels
contain glands in the esophagus and duodenum ( brunners gland )
Submucosal plexus —> meissners plexus
where are parasympathetic ganglia concentrated in GIT tract?
the walls
what is the function of meissners plexus?
induce peristalsis
stimulates mucosal glands
what is the plexus found in the two layers of muscularis externa ? ( circular and longitudinal )
myenteric plexus/ auerbach plexus
which fibers supply the surrounding smooth muscles of muscularis externa?
Postganglionic fibers
what are sphincters in muscularis externa?
some areas have thicker smooth muscles
circular muscles open and closes the opening
what is special about muscularis externa in the stomach?
It has an extra inner OBLIQUE layer
So
outer : longitudinal
Inner : circular
innermost : oblique
describe the adventitia and serosa?
Adventitia : in retroperitoneal organs : consist of only loose connective tissue
Serosa : in intra- peritoneal organs :
mesothelial lining —> simple squamous / peritoneum
over a layer of loose connective tissue secretes slippery fluid
plenty of adipose tissue
what is the function of epithelium?
permeability barrier between gut lumen and blood
Transport and digest food
secretion of enzymes
absorb nutrients
Produce and secrete hormones involved in digestion
what are mucosal forms in GIT?
protective
Secretory
Absorptive
where is protective mucosa found ?
oral cavity
pharynx
Esophagus
anal canal
it is stratified squamous surface epithelium
where is the secretory mucosa found ?
stomach
tubular glands are present in the mucosa
where is the absorptive mucosa found ?
small intestines
contain :
villi
glands in the crypts ( crypts are space between the villi )
in duodenum some crypts extend through the muscularis mucosa to form submucosal mucous glands called brunners gland
what are the features of esophagus mucosa and submucosa?
folded mucosa which disappear when distended
Folded mucosa
what epithelium is the esophagus?
stratified squamous non keratinized epithelium
what is found in the lamina propria of esophagus?
Papillae
mucous glands —> plenty near junction with the stomach to protect from acidity
describe the muscularis mucosa of esophagus ?
Poorly developed in the upper parts
well developed in caudal/lower parts
what is present in submucosa of esophagus?
compound tubulo - alveolar mucous gland
Which are also found in duodenum
describe the muscularis externa?
Upper esophagus : only skeletal muscle
Middle esophagus : Mixture of skeletal and smooth muscles
Lower esophagus : Smooth muscles
describe the adventitia of esophagus?
adventitia surrounds the entire esophagus except the abdominal part
the abdominal part when it enters the diaphragm it becomes surrounded by peritoneum —> Serosa
what happens the gastro-esophageal junction ?
Abrupt transition of mucosa
Stratified squamous —> glandular secretory mucosa simple columnar cells
The muscularis mucosa and submucosa and muscularis externa continue uninterrupted beneath the mucosal junction so they stay the same
what sphincter does the muscularis externa form ?
a physiological sphincter
not anatomical there’s no thickening
describe the interior of the stomach?
in non distended state , the stomach mucosa is thrown into prominent longitudinal folds called RUGAE which permit great distension after eating
Mucosa show tiny grooves —> gastric pits
Gastric glands open into the bottom of the gastric pits
what happens at the gastroduodenal junction ?
the pylorus terminate to form a strong muscular ANATOMICAL SPHINCTER
describe the epithelium of the mucosa of the stomach?
Surface mucus cells / simple columnar cells —> invaginates into lamina propria forming GASTRIC PITS
NO GOBLET CELLS
Gastric glands are found at the base of pits
Cardiac, gastric and pyloric glands differ
cardiac –> Coiled mucous glands
gastric —> straight glands
Pyloric glands —> coiled mucous glands
what is the content of lamina propria of the mucosa of stomach?
loose connective tissue
Smooth muscle
lymphocytes
gastric glands
open to the gastric pit
what is the content of muscularis mucosa of the stomach?
inner circular
outer longitudinal
describe gastric pits and glands?
simple columnar epithelium of mucous cells
oval nucleus basal
Many mucous granules in apical cytoplasm
mucous layer protects stomach epithelium from acid BUT IT IS NOT FROM GOBLET CELLS IT IS FROM SURFACE MUCOUS CELLS
Describe the gastric glands of cardiac region ?
simple or branched tubular cardiac glands WITH LARGE LUMEN AT TERMINUS open into gastric pits
Shallow –> mostly mucous cells and few parietal cells –> poorly developed glands
often has esophagus attached
describe the gastric pit of the fundus/body?
Gastric pits = narrow and shallow
Glands long and straight ( Well developed)
many parietal and chief cells
Neck of gland : has undifferentiated cells and mucous cells
Base of gland : have parietal cells and chief cells and enterochromaffin cells
what are the glands of the funuds?
undifferentiated cells /stem cells
mucous neck cells
parietal / oxyntic cells
ECL/enterochromaffin cells
Chief cells
describe the undifferentiated cells /stem cells?
Neck of gland
oval
basal nuclei
distinct nucleolus
mitotic
Stem cells
Surface cells survive for 3-7 days
describe mucous neck cells?
Low columnar
basal nuclei irregular
Mucous granules
Secrete mucous
describe parietal/oxyntic cells?
Large pyramidal cells with acidophilic cytoplasm
Secrete HCL and gastric intrinsic factor necessary for absorption of vitamin B12 in the ilium which is essential for erythropoiesis
situated in the upper half of gland
many mitochondria
Eosinophilic
intercellular
canaliculi
describe ECL/ Enterochromaffin cells?
seen near base of glands
secrete histamine
describe chief cells?
deeper glands
basophilic
ribosomes
Secrete pepsinogen
describe pylorus glands and pits?
deep and open gastric pits
short coiled glands
NO CHIEF CELLS
mucous cells : to protect duodenum from acid
few parietal cells
Neuroendocrine cells ( G cells ) which secrete gastrin
describe muscularis externa of the stomach?
3 layers
Innermost : oblique
Inner : circular
Outer : longitudinal
describe the serosa of the stomach?
thin layer of adventitia without covering of mesothelium
what transition to the mucosa happen at pyloric sphincter?
From glandular arrangement of the stomach ——> villous arrangement which is a characteristics of small intestines
The duodenum is distinguished by mucus secreting glands ( brunners gland ) which are found in the submucosa ) + goblet cells ( no goblet in stomach ) + villi + microvilli
describe the muscularis externa of the pyloric sphincter in the gastroduodenal junction?
Consist of marked thickening of CIRCULAR layer of the muscularis externa
also has goblet cells and villi and microvilli
