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
GL cells
stomach, SI, LI; secrete glicentin
I cells
SI; secrete cholecystokinin
K cells
SI; gastric inhibitory peptide
Mo cells
SI; secrete motilin
N cells
SI; secrete neurotensin
PP (F)
stomach, LI; secrete pancreatic polypeptide
S cells
SI; secrete secretin
VIP cells
stomach, SI, LI; secrete vasoactive intestinal peptide
SI segments
duodenum, jejunum, ileum
pH of stomach vs intestines
stomach - low pH
duodenum = high pH
plicae circulares
transverse-oriented folds in SI; they add increased surfacearea for absorption; also covered in villi and microvilli
Glands in intestine
Brunner’s glands, crypts of Lieberuhn
Paneth cells
contain eosinophilic granules with antibacterial peptides (defensins+lysozymesand phospholipase)
crypts of Lieberkuhn
penetrate from base of villi deeper into mucosa
Brunner’s glands
only in duodenum and secrete large amounts of bicarbonate contents into crypts and mucins
Peyer’s patches
lymphatic nodules/groups of nodules in mucosa of intestine
M cells
special epithelial cells take up antigens and phagocytose luminal contents to presnt antigens to underlying lymphocytes/macrophages
plasma cells of Peyer’s patches
release IgA class immunoglobulins that bind receptors and transcytosed to lumenal surface to act as antibacterial agents
where are plicae circulares best developed?
jejunum
villi of SI most common in
duodenum> jejunum > ileum
function of pancreas
exocrine pancreas secretes digestive enzymes
which 2 enzymes released in active form
amylase (degrades starch to glucose and maltose) and ribonuclease (cleave RNA)
what enzymes control secretion
secretin, cholycystokinin
what nerves innervate muscularis externa of small intestine
Efferent fibers of myenteric plexus of Auerbach; clusters of ganglion cells between 2 layers of externa
how is large intestine different than small
smooth lumenal surface, no plicae/villi
- numerous straight tubular glands or crypts
- 2 cell types in epithelium (mucous producing cells and absorptive cells)
main LI function
salt and water recovery
role of taeniae
muscular specializations in longitudinal layer whose contraction causes sacculation of bowel to compress/segment fecal material
3 main salivary glands
paired submandibular, sublingual, and paired parotid
type of fluid parotid gland secretes
serous
type of fluid submandibular gland secretes
mixed serous/mucous
Type of fluid secreted by sublingual gland
mucous
M cell
cell resp for transporting Ag reacting with IgA across to local dendritic cells for adaptive immune response
why enzymes on surface of enterocytes
so that it is near where nutrients are to be taken up so that the aren’t just fed to bacteria
what enzymes on surface of enterocytes in small intestine
lactase, maltase, sucrase
why don’t amylase/RNAse produced as zymogens
none of their targets in ducts
fat digestion
degrade to monosaccharides, take up and modify them as they cross to basal cell and go into lacteals
enterocytes role with IgA
secrete IgA
