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GI > 19. Histology of the Lower GI > Flashcards

19. Histology of the Lower GI Flashcards

1
Q

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

A

Plicae circulares
Villi
Microvilli

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2
Q

What are plicae circularies? How much increase in SA

A

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

Increase the surface area 2-3 fold

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3
Q

What are villi? How much do they increase SA?

A

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

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4
Q

What are microvilli?

A

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

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5
Q

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

A

400-600 fold

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6
Q

What is present in the center of the villus?

A

Smooth muscle fibers
Loose CT
Lymphoid cells

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7
Q

What are the 3 difference cells found lining the villi?

A 
Absorptive cells (enterocytes) **
Goblet cells 
DNES (enteroendocrine)
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8
Q

What three cells are found in the Crypts of Lieberkuhn?

A

DNES (enteroendocrine)
Stem cells
Paneth cells

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9
Q

What are the most abundant cells in the small intestine?

A

Absorptive cells/enterocytes

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10
Q

What kind of cells are absorptive cells?

A

Columnar epithelial cells (25 uM high with elongated nuc)

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11
Q

What is the principal function of enterocytes?

A

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

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12
Q

What are the microvilli coated in?

A

Glycocalyx coat made of glycosylated membrane proteins

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13
Q

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

A

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

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14
Q

How can goblet cells be recoginzed on H and E?

A

Full of carbohydrate and remain unstained

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

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15
Q

What do goblet cells secrete?

A

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

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16
Q

What happens when mucin granules are released from goblet cells?

A

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

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17
Q

What does Ki-67 stain?

A

Proliferating cells

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18
Q

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

A

Lamina propria

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19
Q

What are the cells in the crypts of lieberkuhn?

A

Enteroendocrine cells
Paneth cells
Stem cells

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20
Q

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

A

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

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21
Q

The intestinal epithelium is replaced every ___ days?

A

3-6 days

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22
Q

How can stem cells be identified in the crypts?

A

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

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23
Q

What secretes lysozyme and defensins?

A

Paneth cells

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24
Q

Where are paneth cells found?

A

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

25
Q

Staining of paneth cells

A

Stain with eosin

Phloxine-tartrazine stains the secretory granules scarlet

26
Q

How can EC cells be distinguished from paneth cells?

A

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

27
Q

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

A

Lamina propria

28
Q

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

A

Contract to cause shortening of the villus during digestion

Important for emptying of the lacteal

29
Q

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

A

Gut-Associated Lymphoid Tissue (GALT)

30
Q

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

A

Lymphoid nodules

31
Q

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

A

Peyer’s Patches

32
Q

Where are Peyer’s Patches most commonly found?

A

Ileum (some in the jej)

33
Q

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

A

Submucosa

34
Q

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

A

large numbers of BRUNNER’S GLANDS

35
Q

What are Brunner’s glands?

A

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

36
Q

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

A

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

37
Q

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

A

Neural control from Meissner’s plexus

Hormonal control from enteroendocrine cells

38
Q

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

A

Myenteric/Auerbach’s plexus

39
Q

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

A
  1. Mixing contractions: expose chyme to digestive juices

2. Propulsive contractions: peristaltic waves of muscle movement (transports chyme at 2cm/min)

40
Q 
In each day, the SI absorbes:
\_\_ L fluid
\_\_ g sodium
\_\_ kg carbs/protein
\_\_ kg fat
A

7 L
30 g
0.5 kg
1 kg

41
Q

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

A

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

42
Q

What is the main distinguishing feature of the duodenum?

A

Brunner’s glands in the submucosa

**also fewer goblet cells

43
Q

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

A

Narrower, shorter, sparser

**more goblet cells

44
Q

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

A

Sparsest, shortest, and narrowest

45
Q

What is the most distinctive feature of the ileum?

A

Peyer’s patches in the ileum

**in the region of the Peyers patches, villi may be reduced in height or absent

46
Q

How long is the large intestine? Parts?

A

1.5 m

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

47
Q

Why is the surface of the colon relatively smooth?

A

Not folded into plicae circularis and villi

48
Q

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

A

Paneth cells

49
Q

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

A

Longer crypts

Highly glandular, with an abundance of goblet cells

50
Q

How often is the colonic mucosa replaced?

A

Replaced every 6-7 days

51
Q

How does the muscularis mucosae of the colon differ?

A

Better developed, with clear circular and longitudinal fibers

52
Q

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

A

Taenia coli

Haustra coli

53
Q

What is characteristic of appendix histology?

A

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

54
Q

How does the rectal mucosa compare to colonic mucosa?

A

Crypts are deeper and goblet cells are more abundant

55
Q

What transition occurs at the recto-anal junction?

A

Epithelium transitions from simple columnar to stratified squamous

56
Q

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

A

Large circumanal glands

57
Q

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

A

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

58
Q

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

A

Internal: smooth muscle
External: striated muscle

59
Q

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

A

Colon

GI (28 decks)

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