Lecture 30: microstructure GI Flashcards Preview

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Flashcards in Lecture 30: microstructure GI Deck (42):

Four layers of GI tract

1. mucosa (innermost lining)
epithelial lining cells
lamina propria
muscularis mucosae
2. Submucosa (supports the mucosa)
loose tissue; contains blood vessels, nerves, lymphatics
3. Muscularis propria (muscle proper)
inner circular muscle, outer longitudinal muscle
4. Serosa (thin outer lining)


What are the functions of the two layers of muscularis propria

inner circular muscle --> Contracts food
outer longitudinal muscle --> propels muscle


myenteric plexus vs. submucosal plexus

Nerves are clustered in two different areas of the tract, differentiated by function.
Myenteric (also called auerbach's plexus) between two muscle proper layers. Well represented throughout the gut, muscles needed in all of alimentary canal.
Submucosal/Meissners above submucosa, mostly seen in small intestine in large intestine, more functional in absorption/digestion.


Enteric Nervous System

Own nervous system of gut. Nerves arise in gut, communicate with other nerves. Can work without communication from CNS, seen paraplegic patients with spinal cord injuries.


parasympathetic vs. sympathetic innervation of the gut

sympathetic go through pre-vertebral ganglion, while the parasympathetics communicate directly through one nerve system.


Key features histo of exophagus

stratified squamous epithelium (non-keratinized)
muscularis propria varies --> upper 1/3 skeletal, middle 1/3 mixed, lower 1/3 smooth
No serosa here.


Squamo-columnar junction

Between stomach and esophagus, the squamous epithelium abruptly transitions to the columnar epithelia of the stomach.
But only the epithelia transitions, the lamina propria and rest of mucosa stays the same.


key structural features of the stomach

Parietal cells --> secrete acid; intrinsic factor
chief cells --> secrete pepsinogen
G cells --> secrete hormone gastrine
Mucous cells --> protect, lubricate mucosa
Muscularis propria --> 3 layers, additional oblique layer


Part of stomach that is reservoir

Fundus and body, also where acid is added


Part of stomach that does mechanical digestion

Mixing and Grinding of food happens in antrum


Three types of glands in stomach

Fundic --> in fundus and body of stomach
Pyloric --> antrum and pyloric
Cardiac --> proximal stomach


What are in fundic glands

long branched glands with mucous, parietal, chief, and endocrine glands


Contents of Pyloric glands

Mucous and endocrine glands, long branched glands


Contents of cardiac glands

short branched tubular glands, mostly mucuous glands


Gastric pits

The pit is leading to the gland, seen in the folds of the stomach. Lined with mucous producing cells to protect the stomach from acid produced by stomach.


Foveolar cells

Located at surface line the gastric pits, mucous cells with faint, pink cytoplasm; rectangular shape


Mucous neck cells

located at base of gastric pits; pale mucous vacuoles


parietal cells

located lower in fundic gland; eosinophilic cytoplasm with central nucleus ("fried egg" appearance); lots of mitochondria lead to v. pink cytoplasm. PM lots of invaginations


Chief cells

Located near parietal cells, pyramidal cells with more basophliic cytoplasm (lots of RER), have granules


Endocrine cells

Seen with special IHC stains, eosinophilic granules


Stem Cells

located in mucous neck region


Small Intestine, key structural features

Highly adapted for maximal srface area
very long organ (15-18 feet)
folds of mucosa/submucosa (not muscularis propria)
mucosa has finger-like projections (villi)
epithelial cells have microvilli


Villi vs. Crypts

Villi are extensions up of tissue, crypts are folds into tissue. both are present in small intestine. Usually 4:1 height ratio of villi:crypt


Villi features

Finger like extensions into lumen of small intestine. Site of absorption. The lamina propria is rich in blood vessels, lymphatics, nerves.
Central core of lamina propria has lacteal (lymphatic channel), tendons of muscularis mucosae (give villi structural integrity). Things can be absorbed directly into veins or lymphatics.



Are invaginations that are continuous with villi in small intestine.
Site of secretion of fluids and electrolytes.
Paneth cells found at base --> make lots of defensive substances against dangerous substances in lumen, especially the nearby stem cells.
Stem cells found in crypt, cells born here and mature as they migrate up the crypt.


Can villi move?

Yes have muscles (muscularis mucosae) which also give it structural integrity.


what makes up the brush border

Microvilli membrane, found on columnar cells of the small intestine. have actin filaments inside. Have enzymes critical for digestion of certain food (lactose).



Other word for columnar absorptive cells of small intestine.
Have microvilli.
Tall cells with basal membrane.
Junctional complexes --> attach cells
intercellular clefts --> spaces between enterocytes, at base of cells.



Encapsulate fat, go into lymphatic channels.


Panneth cells in histo

v. obvious pink granules


duodenum functions

neutralize acidic chyme that exits the stomach through secretions of the brunners glands, which secrete alkaline mucus from submucosal cells.
Also the site of absorption of most minerals


Jejunum function

absorption of most nutrients


ileum function

absorption of many nutrients.
absorb B12 and bile proteins.
Peyers patches (lymphoid aggregates) seen here


Why does colon need to be strong?

Bc it has to move solidified stool. Tenia coli are the longitudinal muscles seen in the colon, are now arranged in rings. instead of longitudinal to increase strength.


Function of colon

Absorb water, solidify the stool


Histo structures of colon

No villi, only crypts in mucosa. Mostly goblet cells. Muscularis propria has tenia colia (3 layers) of longitudinal muscle.


Cell types of colon

Mostly goblet cells
Columnar absorptive cells
rare enteroendorcine cells
rare paneth cells (even though there are lots of bacteria in the colon)
Stem Cells seen in base of crypt


anal canal junction

squamo-columnar junction. Anal canal has squamous stratified
rectum has columnar


Anal Canal functions

Controls continence


Key structural feature of anal canal

mucosa has stratified squamous epithelium


two parts of anal sphincter

external anal sphincter --> skeletal muscle, coluntary
internal anal sphincter --> smooth muscle, continuous with colonic muscle, involuntary.


Villus vs. Crypt cells of small intestine

Villus cells are columnar, have microvilli/terminal web, Golgi/ER
Crypt Cells are cuboidal, no microvilli/terminal web/golgi-ER