Lower GI VM

Question 1

What are four ultrastructural features of enterocytes that contribute to their absorptive function?

Answer 1

• 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

Question 2

What unique structure can be found in the submucosa of the duodenum?

Answer 2

Submucosal Glands (of Brunner)

Recall: The esophagus is the only other site in the GI tract that contains submucosal glands.

Question 3

What do Brunner’s glands secrete?

Answer 3

Alkaline mucous to neutralize acidic chyme

Question 4

1. What term is used to describe the diffuse, unencapsulated lymphoid tissue in the GI tract?
2. Specifically, where can this lymphoid tissue be found within the GI tract tissue layers?
3. How does this lymphoid tissue appear histologically?

Answer 4

1. Gut-Associated Lymphoid Tissue (GALT)
2. In the submucosa and lamina propria of the mucosa.
3. Clusters of basophilic cells

Question 5

What tissue layers are the microvilli of the small intestine composed of?

Answer 5

Lamina propria & the overlying epithelium

Question 6

1. What are the spaces between microvilli termed?
2. What tissue layers can be found in these spaces?

Answer 6

1. Intestinal Crypts (of Lieberkuhn)
2. Lamina propria & epithelium (like the villi), plus muscularis mucosa at the crypt bases

Question 7

What type of epithelium covers a villus?

Where in the upper GI tract can this type of epithelium also be found?

Answer 7

Simple columnar

Also in the stomach

Question 8

What is primary cell type of the intestinal epithelium? What are its functions?

Answer 8

Enterocyte

• Nutrient absorption
• Digestive enzyme production

Question 9

What is the specialized apical plasma membrane of the intestinal epithelium called?

Answer 9

Brush border

Many microvilli for increased surface area of nutrient absorption

Question 10

True or False:

The submucosa extends into the core of a villus.

Answer 10

False

Question 11

What intestinal epithelial cell type that secretes mucous?

What stain can readily detect these cells?

Answer 11

Goblet cells

The PAS stain will turn the carbohydrate in goblet cells a magenta color

Question 12

1. What epithelial cell type is found in the base of intestinal crypts?
2. How do these cells stain on H&E?
3. What ultrastructural feature is prominent in these cells?

Answer 12

1. Paneth cells
2. Eosinophilic
3. Secretory granules in their apical cytoplasm

Question 13

True or False: Paneth cells migrate from the crypts to the villus epithelium.

Answer 13

False

Question 14

What is the function of Paneth cells?

Answer 14

Bacterial & viral defense, via secretion of lysozyme and defensins

Question 15

1. How do enteroendocrine cells stain on H&E?
2. What notable ultrastructural feature do they possess?

Answer 15

1. Typically, clear cytoplasm
2. Basal secretory granules

Question 16

Explain (don’t just point out) the difference in polarity of the secretory granules in Enteroendocrine cells vs. Paneth cells

Answer 16

Enteroendocrine cells have basal granules because they secrete into the bloodstream.

Paneth cells have apical granules because they secrete into the gut lumen.

Question 17

What laboratory method can be used to identify enteroendocrine cells in a histological section of the intestine?

Answer 17

Immunostaining

[I feel like you could hypothetically immunostain anything if you wanted to, but that’s what’s in the lab notes.]

Question 18

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?

Answer 18

Stem cells!

Presence of mitotic figures

Question 19

In the musclaris externa of the intestine, what is the orientation of the inner muscle layer?

The outer layer?

Answer 19

Inner: Circular

Outer: Longitudinal

Question 20

What are the functions of the intestine’s muscularis externa?

Answer 20

Contraction provides:

• Mixing of chyme with digestive enzymes
• Propulsion of chyme (peristalsis)

Question 21

1. Where would you find a ganglion of the myenteric (Auerbach’s) plexus?
2. How would the ganglion appear histologically?
3. How would this ganglion differ from a ganglion of Meissner’s plexus?

Answer 21

1. Between the layers of the muscularis externa
2. Histologically:
   
   • Cluster of large basophilic cells
   • Large nuclei and prominent nucleoli
3. 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.]

Question 22

Which parasympathethetic nerve(s) innervate(s) the myenteric plexus within the foregut derivatives of the GI tract?

The midgut derivatives?

The hindgut derivatives?

Answer 22

Foregut: CN X

Midgut: CN X

Hindgut: S2-S4

Question 23

What is the name for the large intestinal folds of the jejunum?

What tissue layers compose these folds?

Answer 23

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.

Question 24

1. What is the purpose of the plicae circulares?
2. How do these folds differ from rugae?

Answer 24

1. Slow the passage of intestinal contents and increase the surface area for absorption.
2. Unlike rugae, these folds are not obliterated by intestinal distension.

Question 25

True or False: The jejunum contains submucosal glands of Brunner.

Answer 25

**False**. Remember - only the esophagus and duodenum!

Question 26

1. What histological stain can be used to readily detect the presence of neurons? 2. What specifically does the stain bind? 3. 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?

Answer 26

1. **Cresyl Violet** 2. Stains neuronal **rough ER** (aka **Nissl substance**) 3. **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.**

Question 27

What ultrastructural feature can be noticed in the center of each villus? What is the purpose of this feature?

Answer 27

**Lacteal**, a **lymphatic** capillary used for the absorption of dietary **fats** (in the form of **chylomicrons**.)

Question 28

What is the name for a localized aggregation of lymphoid tissue (GALT) in the small intestine?

Answer 28

**Peyer's Patch**

Question 29

What type of epithelium lines the lumen of the colon?

Answer 29

Again **simple columnar**, but **non-villous**

Question 30

Name two nutrients absorbed by enterocytes in the epithelium of the large intestine.

Answer 30

1. Water 2. Electrolytes

Question 31

Aside from enterocytes, what other epithelial cell type has a significant presence in the colon, and why?

Answer 31

**Goblet cells** Secretion of **mucous** to facilitate the passage of feces through the large intestine.

Question 32

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?

Answer 32

The appendix! Like the intestines, the appendix is also lined with **simple columnar** epithelium.

Question 33

What is the general term for varicose dilations of the rectal venous plexus?

Answer 33

Hemorrhoids