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Flashcards in Structures of Lower GI Tract Deck (34):
1

What are the three regions of the small intestine?

Duodenum
Jejunum
Ileum

-These are all histologically similar but minor differences permit their identification.

2

Name 3 modifications of the small intestine that increase its surface area to aid in absorption.

1. Plicae circulares
2. Villi
3. Microvilli
** These three specialized modifications increase the intestinal surface area by 400-600 fold

3

Permanent mucosal folds present in the duodenum, jejunum and proximal ileum -- increase surface area by 2-3 fold

Plicae circularis

4

Finger-Like projections of epithelium-covered lamina propria that increase surface area by 10-fold

Villi

5

Extensions of the epithelial cell apical plasma membrane that increase surface area 20-fold

Microvilli

6

Villi are extensions of the....

Lamina propria
They contain a central lymphatic channel and several capillaries

7

Epithelial covering of the villi are composed of:

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

8

Extend from the base of the villi into the lamina propria

Crypts of Lieberkuhn
Contain: DNES (enteroendocrine) cells, stem cells, paneth cells

9

What is the most abundant cell of the small intestine?

Absorptive cells/enterocytes -- they are columnar epithelial cells with an elongated nucleus

10

What is the principal function of the enterocytes?

Terminal digestion
Absorption of water and nutrients
They re-esterify fatty acids into triglycerides, form chylomicrons an transport the bulk of the absorbed nutrients into the lamina propria for distribution

11

What is in the brush border of the luminal surface of each enterocyte?

Microvilli covered in glycocalyx -- has protective role but also involved in digestions of disaccharides and dipeptides

12

What do Goblet cells secrete?

Mucin = high MW glycoprotein macromolecules that have 20% protein and 80% carbohydrate

After releases mucin granules become hydrated and expand several hundred fold in volume -- this mucus lubricates and protects the intestine

13

In the Crypts of Lieberkuhn, explain how cell type differs between the upper and lower regions?

Upper: surface absorptive and Goblet cells
Basal: No surface absorptive cells and only a few Goblet cells, most of the cells are regenerative, DNES cells and Paneth cells

14

How often is the intestinal epithelium replaced?

Every 3-6 days

15

What do Paneth cells secrete?

Lysozyme and defensins

*Paneth cells are long lived and do not participate in upward migration of epithelial cells

16

Highly vascularized to accept the products of absorption -- also contains abundance of lymphoid cells that protect the intestinal lining from microbial invasion

Lamina propria

17

Contains an inner circular and outer longitudinal layer of smooth muscle fibers -- during digestion these fibers contract causing shortening of the villus

Muscularis mucosae

18

Lamina propria's extensive immune defense system
Individual lymphocytes within the mucosa and epithelium or regions of coalesced lymphoid nodules

GALT = gut-associated lymphoid tissue

Consists of individual lymphoid nodules and Peyer's patches

19

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

It has a large number of Brunner's glands -- secrete alkaline mucus that neutralizes the pH of gastric chyme and protects the duodenum
Also contains epidermal growth factor that may be involved in stem cell proliferation in the crypts

20

What controls the release of secretions from the intestines?

Submucosal (Meissner's) Plexus

21

What lies between the smooth muscle layers of the muscularis external?

Myenteric (Auerbach's) Plexus -- peristaltic movement

22

How do the 3 regions of the small intestine differ?

Duodenum: shortest segment; villi are broader, taller and more numerous per unit area; fewer goblet cells; Brunner's glands in submucosa

Jejunum: villi are narrower, shorter and sparser than the duodenum; number of goblet cells per unit area is greatest

Ileium: villi are sparsest, shortest and narrowest of all three regions; lamina propria houses Peyer's patches in the wall

23

Components of the large intestine

Cecum, appendix, colon (ascending, transverse, descending and sigmoid), rectum and anus

24

How does the colon differ from small intestine?

Not fold into plicae circularis and villi are absent from the mucosa giving it a smooth surface

Also no Paneth cells

25

Crypts of Lieberkhun in the Large intestine

Crypts are longer and highly glandular with lots of Goblet cells

Open into the lumen at the surface of the colon and can be seen as a regular array of holes across the mucosa

26

How does the muscularis mucosa in the colon differ from that in the small intestine?

Better developed with clear circular and longitudinal fibers

Outer longitudinal muscle is arranged in 3 distinct bands called taenia coli that remain partially contracted and cause the intestine to be puckered into sacculations called haustra coli

27

Blind-ended tube extending from the cecum distal to the ileocecal junction

Appendix -- has masses of lymphoid tissue in mucosa and submucosa, which often forms follicles with germinal centers

28

What change happens at the end of the rectum where it joins the anal canal?

Epithelium transitions from simple columnar to stratified squamous
Crypts disappear and are replaced by large circumanal glands

29

Venous plexi found in the submucosa of the anal canal

1. Internal hemorrhoidal plexus
2. External hemorrhoidal plexus

30

Duodenum

Brunner's glands in submucosa

31

Ileum

Villi and crypts
Peyer's patches

32

Colon

Just Crypts
No paneth cells

33

Appendix

Lymphoid tissue

34

Anus

Squamous epithelium
Glandular