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Flashcards in GI Histology Deck (23)
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4 layers of GI tract

1. mucosa:
epithelial layer; loose well vascularized CT called Lamina Propria (w/ lymphocytes, plasma cells, and mac); underlying SM called muscularis mucosae

2. submucosa:
denser CT, larger bv, nerve plexuses, glands, lymphatic nodules. lymphoid cells

3. muscularis externa
inner circular and outer longitudinal SM and nerve plex

4. serosa/adventitia: serosa: squamous epi cells separated from muscular layers by thin CT
adventitia: esophagus above diaphragm where outer squamous layer is absent


What is esophagus lined with?

non-cornified squamous epithelium
upper portion: skeletal muscle (vol)
midway: mix of skel/SM
lower 1/3: SM

mucous glands in mucosa and submucosa


3 zones of stomach

cardia: mucus secreting glands around entry of esoph
fundus: body of stomach: secretes acid, peptic digestive prod/mucus.
Pyloris: secretes mucus, many endocrine cells that secrete gastrin

*outer muscularis externa has 3rd oblique layer of SM (lumenally to circular)


Rugae or plicae mucosae

longitudinal folds, disappear upon distension


Histologic folds of stomach

epithelial folds with spaces called "gastric pits"
Gastric glands at bottom of pits and into mucosa


Stem cells of stomach, surface mucous cells, chief cells, glycocalyx

stem cells: upper neck region
surface mucous cells: w/ large vesicles full of stomach mucins and bicarb are discharged and act as protective layer (shelter epithelial cells from acid and abrasion from chyme)
Glycocalyx: Directly covering the short microvilli of
these surface cells is a more structured layer of cell surface glycoproteins, the glycocalyx

chief cells: protein secretors with apical granules and basal RER
---secrete pepsinogen (conv to pepsin in acid's presence)


Parietal cells

acid producing cells
pump H+ ions using H/K -ATPase
-steep gradient so high energy cost
-lots of mitochondria.

-also secrete IF for B12 absorption


What stimulates parietal cells to secrete acid?

gastrin and histamine


Zollinger Ellison syndrom

excessive secretion of gastrin results in overproduction of HCl by parietal cells--> duodenal ulcers


Enteroendocrine cells

in family: APUD cells
G cells: secrete gastrin, located in pylorus
A cells: secrete glucagon
EC cells: secrete serotonin
Dcells: somatostatin secreting



vasoactive instestinal peptide
-increase peristaltic action of small and large int
-stimulates elim of water and ions by GI tract


Small intestine: large surface area

plicae circulares: project into lumen, covered in villi. Microvilli on surface of enterocytes (epithelial cells). Glycocalyx over microvilli surface into which glycoproteins of plasma membrane extend

Goblet mucous cells are scattered between absorptive/digestive cells. Least abundant in duodenum


Crypts of Lieberkuhn

intestingal gland (simple, tubular)
penetrate from base of villi deeper into mucosa.


Paneth cells

contain large eosinophilic granules, containing antibacterial peptides called defensins + lysozyme and phospholipase


Brunner's glands

found only in the duodenum and release their contents into the crypts.
-secrete bicarb to neutralize acid arriving thru pyloric sphincter
-also secrete mucins


M cells (specialized epi cells)

function as antigen-uptake cells,
and phagocytose luminal contents and present antigens to
underlying lymphocytes and macrophages


Type of immunoglobulins secreted in gut?



Duodenum, jejunum, ileum and brunner's glands, goblet cells, lymphatic tissue, plicae circulares, villi

Brunners: present
goblet cells, lymphatic tiss, plicae circulares: +
number of villi: most numerous

Brunner's: absent
goblet cells, lymphatic tiss: ++
plicae circulares: best developed
number of villi: decrease distally

brunner's: absent
goblet cells: +++
lymphatic tissue: ++++
Plicae: +
microvilli: less abundant


Exocrine pancreas

secretes digestive enzymes
gland organized into acini (acinar cells)
apical portion full of secretory granules (zymogen granules)

trypsin, chymotrypsin, elastase,
carboxypeptidase, and triacylglycerol lipase (trpsinogen into trypsin by enterokinase, then trypsin activates all the others)

amylase and ribonuclease are secreted by panc in active form


Centroacinar cells

found in the acini
beginning of duct systme


duct cells

secrete water and bicarb (help Brunner's glands neutralize acid)

secretion under control of secretin and CCK


What does LI lack that SI has?

lacks plicae and villi

numerous straight tubular glands or crypts
-epithelial layer has two cell types, abundant mucous producing
cells and absorptive cells
-main func: recovery of water and salt

bands: called taeniae

internal anal sphincter: thickened circular layer
external anal sphincter: circular striated muscle


Salivary glands

submandibular (paired)-- mixed
sublingual-- mucous
paired parotid glands-- serous (watery w/ enz amylase, RNAse, DNAse; also trans IgA)