19. Histology of the Lower GI

Question 1

What are the three main modifications of the luminal surface of the SI that increase the SA to aid absorption?

Answer 1

Plicae circulares
Villi
Microvilli

Question 2

What are plicae circularies? How much increase in SA

Answer 2

Permenant mucosal folds in the duo, jej, and prox ilieum

Increase the surface area 2-3 fold

Question 3

What are villi? How much do they increase SA?

Answer 3

Finger-like projections of epithelium-covered lamina propria, contain central lacteal and several capillaries
Increase the SA by 10 fold

Question 4

What are microvilli?

Answer 4

Extensions of the epithelial cell apical plasma membrane that increase the surface area 20 fold
(increase the SA by 20 fold)
**3,000 on each epithelial cell

Question 5

How much do plicae circulares, villi, and microvilli cumatively increase the SA?

Answer 5

400-600 fold

Question 6

What is present in the center of the villus?

Answer 6

Smooth muscle fibers
Loose CT
Lymphoid cells

Question 7

What are the 3 difference cells found lining the villi?

Answer 7

Absorptive cells (enterocytes) **
Goblet cells 
DNES (enteroendocrine)

Question 8

What three cells are found in the Crypts of Lieberkuhn?

Answer 8

DNES (enteroendocrine)
Stem cells
Paneth cells

Question 9

What are the most abundant cells in the small intestine?

Answer 9

Absorptive cells/enterocytes

Question 10

What kind of cells are absorptive cells?

Answer 10

Columnar epithelial cells (25 uM high with elongated nuc)

Question 11

What is the principal function of enterocytes?

Answer 11

Terminal digestion and absorption of water and nutrients
Reesterify fatty acids into triglycerides, form chylomicrons, and transport the bulk of absorbed nutrients into the lamina propria for distribution

Question 12

What are the microvilli coated in?

Answer 12

Glycocalyx coat made of glycosylated membrane proteins

Question 13

What is the role of the glycocalyx that coats the microvilli in the SI?

Answer 13

Protective role
Digestion of disaccharides and dipeptides into monomers for absorptiong through peptide hydrolases and diassachridases that are abundant on the apical surface

Question 14

How can goblet cells be recoginzed on H and E?

Answer 14

Full of carbohydrate and remain unstained

**carb within goblet cells can be identified by PAS stain

Question 15

What do goblet cells secrete?

Answer 15

Copious mucin–high MW glycoprotein macromolecules that have 20% protein and 80% carbohydrate

Question 16

What happens when mucin granules are released from goblet cells?

Answer 16

Hydrated and expand several hundred fold in volume, lubricates and protects the intestines

Question 17

What does Ki-67 stain?

Answer 17

Proliferating cells

Question 18

The crypts of Lieberkuhn extend from the base of the villi into the:

Answer 18

Lamina propria

Question 19

What are the cells in the crypts of lieberkuhn?

Answer 19

Enteroendocrine cells
Paneth cells
Stem cells

Question 20

Where are new cells for the epithelial lining of the intestine generated?

Answer 20

Stem cells in the crypts–migrate up the villus and are exfoliated from the tips of the vilus

Question 21

The intestinal epithelium is replaced every ___ days?

Answer 21

3-6 days

Question 22

How can stem cells be identified in the crypts?

Answer 22

Mitotic figures, since they are the only cells that are proliferating

Question 23

What secretes lysozyme and defensins?

Answer 23

Paneth cells

Question 24

Where are paneth cells found?

Answer 24

Resident at the base of the crypts–do not participate in upward migration of epithelial cells

Question 25

Staining of paneth cells

Answer 25

Stain with eosin | Phloxine-tartrazine stains the secretory granules scarlet

Question 26

How can EC cells be distinguished from paneth cells?

Answer 26

EC cell granules on the basal side for secretion of hormones into the blood Paneth cells have granules at the apical side for secretion into the lumen

Question 27

What area of the mucosa is highly vascularized and accepts the products of absorption? Also contains lymphoid cells to protect from microbial invasion

Answer 27

Lamina propria

Question 28

What is the role of fibers from the muscularis mucosa that enter the vilus and extend to the tip?

Answer 28

Contract to cause shortening of the villus during digestion | Important for emptying of the lacteal

Question 29

Lamina propria maintains an extensive immune defense system in the form of lymphoid tissue called:

Answer 29

Gut-Associated Lymphoid Tissue (GALT)

Question 30

Though most GALT exists as individual lymphocytes in the mucosa and epithelium, what are aggregates called?

Answer 30

Lymphoid nodules

Question 31

What is the structure that forms from the joining of several lymphoid nodules?

Answer 31

Peyer's Patches

Question 32

Where are Peyer's Patches most commonly found?

Answer 32

Ileum (some in the jej)

Question 33

What layer of the SI is moderately dense CT with small numbers of adipose cells

Answer 33

Submucosa

Question 34

How does the duodenal submucosa differ from the rest of the GI tract?

Answer 34

large numbers of BRUNNER'S GLANDS

Question 35

What are Brunner's glands?

Answer 35

Similar to mucous acini, ascend through the muscularis mucosae layer and enter the crypts to deposit secretions into the lumen

Question 36

What is the composition of the secretions from Brunner's glands in the duodenal submucosa?

Answer 36

Alkaline mucus that neutralized the pH of gastric chyme and protects duodenum Epidermal growth factor, increases stem cell proliferation in the crypts

Question 37

What controls secretion of fluid from the SI (2 liters a day)

Answer 37

Neural control from Meissner's plexus | Hormonal control from enteroendocrine cells

Question 38

What nerve plexus is found between the outer and inner layers of the muscularis externa?

Answer 38

Myenteric/Auerbach's plexus

Question 39

What are the two types of movement associated with the small intestine?

Answer 39

1. Mixing contractions: expose chyme to digestive juices | 2. Propulsive contractions: peristaltic waves of muscle movement (transports chyme at 2cm/min)

Question 40

``` In each day, the SI absorbes: __ L fluid __ g sodium __ kg carbs/protein __ kg fat ```

Answer 40

7 L 30 g 0.5 kg 1 kg

Question 41

How do the villi of the duodenum differ from those of the jej and ileum?

Answer 41

Villi are broader, taller, and more numerous per unit area

Question 42

What is the main distinguishing feature of the duodenum?

Answer 42

Brunner's glands in the submucosa | **also fewer goblet cells

Question 43

How do the villi of the jejunum differ from those of the duodenum?

Answer 43

Narrower, shorter, sparser | **more goblet cells

Question 44

How do the villi of the ileum differ from those of the jej?

Answer 44

Sparsest, shortest, and narrowest

Question 45

What is the most distinctive feature of the ileum?

Answer 45

Peyer's patches in the ileum | **in the region of the Peyers patches, villi may be reduced in height or absent

Question 46

How long is the large intestine? Parts?

Answer 46

1.5 m | Cecum, appendix, ascending/transverse/descending/sigmoid colon, rectum, and anus

Question 47

Why is the surface of the colon relatively smooth?

Answer 47

Not folded into plicae circularis and villi

Question 48

Though the colonic epithelium has a similar celluar composition, what cells are absent from the colonic crypts?

Answer 48

Paneth cells

Question 49

How do colonic crypts differ from those in the small intestine?

Answer 49

Longer crypts | Highly glandular, with an abundance of goblet cells

Question 50

How often is the colonic mucosa replaced?

Answer 50

Replaced every 6-7 days

Question 51

How does the muscularis mucosae of the colon differ?

Answer 51

Better developed, with clear circular and longitudinal fibers

Question 52

The musculars externa outer longitudinal muscles are arranged in three distinct bands called: Creates sacculations called:

Answer 52

Taenia coli | Haustra coli

Question 53

What is characteristic of appendix histology?

Answer 53

Masses of lymphoid tissue in the mucosa and submucosa (forms follicles with germinal centers) Mucosal glands are more disperse

Question 54

How does the rectal mucosa compare to colonic mucosa?

Answer 54

Crypts are deeper and goblet cells are more abundant

Question 55

What transition occurs at the recto-anal junction?

Answer 55

Epithelium transitions from simple columnar to stratified squamous

Question 56

What are crypts replaced by at the recto-anal junction?

Answer 56

Large circumanal glands

Question 57

What are the two venous plexi that are found in the submucosa of the anal canal?

Answer 57

Internal hemorrhoidal plexus External hemorrhoidal plexus **can cause hemorrhoids in older people and pregnancy

Question 58

What is the composition of the internal and external anal sphincters?

Answer 58

Internal: smooth muscle External: striated muscle

Question 59

What part of the GI tract has crypts, but no paneth cells?

Answer 59

Colon