Lower GI VM Flashcards
What are four ultrastructural features of enterocytes that contribute to their absorptive function?
- Microvilli for absorptive surface area
- Intercellular junctional complexes to prevent lumenal contents from entering the intercellular space
- Numerous mitochondria - high metabolic activity
- Glycocalyx provides a site for localized extracellular proteolysis as well as protecting the enterocytes from autodigestion
What unique structure can be found in the submucosa of the duodenum?
Submucosal Glands (of Brunner)
Recall: The esophagus is the only other site in the GI tract that contains submucosal glands.
What do Brunner’s glands secrete?
Alkaline mucous to neutralize acidic chyme
- What term is used to describe the diffuse, unencapsulated lymphoid tissue in the GI tract?
- Specifically, where can this lymphoid tissue be found within the GI tract tissue layers?
- How does this lymphoid tissue appear histologically?
- Gut-Associated Lymphoid Tissue (GALT)
- In the submucosa and lamina propria of the mucosa.
- Clusters of basophilic cells
What tissue layers are the microvilli of the small intestine composed of?
Lamina propria & the overlying epithelium
- What are the spaces between microvilli termed?
- What tissue layers can be found in these spaces?
- Intestinal Crypts (of Lieberkuhn)
- Lamina propria & epithelium (like the villi), plus muscularis mucosa at the crypt bases
What type of epithelium covers a villus?
Where in the upper GI tract can this type of epithelium also be found?
Simple columnar
Also in the stomach
What is primary cell type of the intestinal epithelium? What are its functions?
Enterocyte
- Nutrient absorption
- Digestive enzyme production
What is the specialized apical plasma membrane of the intestinal epithelium called?
Brush border
Many microvilli for increased surface area of nutrient absorption
True or False:
The submucosa extends into the core of a villus.
False
What intestinal epithelial cell type that secretes mucous?
What stain can readily detect these cells?
Goblet cells
The PAS stain will turn the carbohydrate in goblet cells a magenta color
- What epithelial cell type is found in the base of intestinal crypts?
- How do these cells stain on H&E?
- What ultrastructural feature is prominent in these cells?
- Paneth cells
- Eosinophilic
- Secretory granules in their apical cytoplasm
True or False: Paneth cells migrate from the crypts to the villus epithelium.
False
What is the function of Paneth cells?
Bacterial & viral defense, via secretion of lysozyme and defensins
- How do enteroendocrine cells stain on H&E?
- What notable ultrastructural feature do they possess?
- Typically, clear cytoplasm
- Basal secretory granules
Explain (don’t just point out) the difference in polarity of the secretory granules in Enteroendocrine cells vs. Paneth cells
Enteroendocrine cells have basal granules because they secrete into the bloodstream.
Paneth cells have apical granules because they secrete into the gut lumen.
What laboratory method can be used to identify enteroendocrine cells in a histological section of the intestine?
Immunostaining
[I feel like you could hypothetically immunostain anything if you wanted to, but that’s what’s in the lab notes.]
Aside from paneth cells, what other cell type can be found in intestinal crypts that does not migrate into the villi?
How would you identify these cells in a histological section?
Stem cells!
Presence of mitotic figures
In the musclaris externa of the intestine, what is the orientation of the inner muscle layer?
The outer layer?
Inner: Circular
Outer: Longitudinal
What are the functions of the intestine’s muscularis externa?
Contraction provides:
- Mixing of chyme with digestive enzymes
- Propulsion of chyme (peristalsis)
- Where would you find a ganglion of the myenteric (Auerbach’s) plexus?
- How would the ganglion appear histologically?
- How would this ganglion differ from a ganglion of Meissner’s plexus?
- Between the layers of the muscularis externa
- Histologically:
- Cluster of large basophilic cells
- Large nuclei and prominent nucleoli
- Location. Recall: Meissner’s plexus = submucosal plexus.
- [The VM handout notes that we may be held responsible for differentiating the two ganglia types based on the surrounding tissue layer.]
Which parasympathethetic nerve(s) innervate(s) the myenteric plexus within the foregut derivatives of the GI tract?
The midgut derivatives?
The hindgut derivatives?
Foregut: CN X
Midgut: CN X
Hindgut: S2-S4
What is the name for the large intestinal folds of the jejunum?
What tissue layers compose these folds?
Plicae Circulares (“Valves” of Kerckring)
The folds are composed of submucosal cores with overlying mucosa. The mucosa has a villous epithelium. The muscularis externa lies deep to the folds.
- What is the purpose of the plicae circulares?
- How do these folds differ from rugae?
- Slow the passage of intestinal contents and increase the surface area for absorption.
- Unlike rugae, these folds are not obliterated by intestinal distension.
True or False: The jejunum contains submucosal glands of Brunner.
False. Remember - only the esophagus and duodenum!
- What histological stain can be used to readily detect the presence of neurons?
- What specifically does the stain bind?
- If you stained a section of intestinal tissue with cresyl violet and saw few or no ganglia, what condition would you worry about the source patient having?
- Cresyl Violet
- Stains neuronal rough ER (aka Nissl substance)
-
Hirshsprung’s Disease
- aka Congenital Agangliosis
- presents with megacolon
- Biospy of affected bowel segment required for diagnosis
- N.B. Though ganglia are absent, often presents with abnormal nerve fiber proliferation in the mucosa.
What ultrastructural feature can be noticed in the center of each villus?
What is the purpose of this feature?
Lacteal, a lymphatic capillary used for the absorption of dietary fats (in the form of chylomicrons.)
What is the name for a localized aggregation of lymphoid tissue (GALT) in the small intestine?
Peyer’s Patch
What type of epithelium lines the lumen of the colon?
Again simple columnar, but non-villous
Name two nutrients absorbed by enterocytes in the epithelium of the large intestine.
- Water
- Electrolytes
Aside from enterocytes, what other epithelial cell type has a significant presence in the colon, and why?
Goblet cells
Secretion of mucous to facilitate the passage of feces through the large intestine.
What part of the GI tract might you suspect you’re looking at if you see an abnormally high concentration of GALT?
What type of epithelium would you expect to see in this area?
The appendix!
Like the intestines, the appendix is also lined with simple columnar epithelium.
What is the general term for varicose dilations of the rectal venous plexus?
Hemorrhoids
