Unit 6 - GI II

Question 1

how is lumenal surface area increased in the small intestine?

Answer 1

1. plicae circularis (valves of Kerckring); 2-3x
2. villi (10x)
3. microvilli (20x)

Question 2

what are plicae circularis?

Answer 2

valves of Kerckring; permanent transverse circular folds of mucosa and submucosa in SI only that increase SA 2-3 times
-most developed in jejunum

Question 3

what are villi VS microvilli?

Answer 3

villi are projections on the surface of epithelium and lamina propria
microvilli are projections of apical plasma membranes

Question 4

how do villi structure progress down the intestines?

Answer 4

• short and broad (leaf-like) in duodenum

- long and finger-like in jejunum and ileum (progressive change, but both are about 0.5 - 1.5 mm tall))

Question 5

what are the 6 major types of cells in the epithelium?

Answer 5

1. absorptive cell (enterocyte)
2. goblet cell
3. enteroendocrine cell
4. paneth cell
5. stem cell
6. M (microfold) cell

Question 6

structure of and location of absorptive cells (enterocytes)

Answer 6

• tall columnar cells with a striated border
• each microvillus is 1 micron tall and 0.1 micron in diameter
• disacc and peptidases are secreted by absorptive cells, and bind to microvilli to break down things for absorption
• lipids absorbed and reesterifid to TGs, converted to chylomicrons, and released from lateral surfaces of lamina propria to be absorbed by central lacteals

Question 7

structure of and location of goblet cells

Answer 7

• unicellular glands that make acid glycoPRO mucins to lubricate and protect the SI
• less abundant in duodenum, and increase in number as one approaches ileum

Question 8

structure of and location of enteroendocrine cells

Answer 8

• unicellular glands that make hormones and vasoactive peptides
• in SI, most occur in basal part of crypts of Lieberkuhn

Question 9

structure of and location of paneth cells

Answer 9

• exocrine cells found in small groups at base of crypts
• apical cytoplasm for innate immunity, filled with large, eosinophilic granules of lysozyme with antibacterial activity that control intestinal flora

Question 10

what disease are paneth cells associated with?

Answer 10

Crohn’s disease

-Paneth cells may be a site of origin for intestinal inflammation

Question 11

structure of and location of stem cells

Answer 11

• located near base of crypts

- move upwards to repopulate crypts and villi in 3-6 days, and paneth cells every 30 days

Question 12

structure of and location of M(icrofold) cells

Answer 12

• only in ileum
• specialized epithelium cells that cover Peyer’s patches
• basement membrane under M cells is discontinuous

Question 13

what is GALT? where is it? what are its components?

Answer 13

makes up 25% of mucosa

• prominent in lamina propria of SI
• made of:
• -Peyer’s patches
• -IgA
• -Secretory component

Question 14

how are Peyer’s patches associated with GALT?

Answer 14

in ileum

• groups of 20-40 lymphatic nodules covered by M cells
• Ag from lumen are taken up by M cells, and delivered to lymphocytes and other cells in Peyer’s patches

Question 15

how is IgA associated with GALT?

Answer 15

synthesized by plasma cells in Peyer’s patches

Question 16

how is secretory component associated with GALT??

Answer 16

SC is 75 kDa glycoPRO made by absorptive cells and inserted in basal plasma membrane

• dimers of IgA bind to SC, enter by endocytosis, and exit apical membrane with SC bound to form secretory IgA
• sIgA binds Ag, toxins, and microorganisms in host defense

Question 17

what are some regional differences in the SI for duodenum?

Answer 17

unique Brunner’s glands in submucosa
-mostly of mucous type
-secretes alkaline mucous that protects VS stomach acid
-provides optimum pH for pancreatic enzyme action
most of duodenum has adventitia b/c retroperitoneal
villi are squared off (like thick cactus leaves)

Question 18

what are some regional differences in the SI for jejunum?

Answer 18

• most highly developed plicae circularis
• villi are longer and more finger like than in duodenum
• more goblet cells
• has serosa, not adventitia

Question 19

what are some regional differences in the SI for ileum

Answer 19

• longest villi and highest number of goblet cells

- Peyer’s patches unique to ileum

Question 20

structure of colon and cecum

Answer 20

• plicae semilunares are temporary folds of mucosa and submucosa
• no villi, only crypts with simple columnar epithelium and striated border
• -goblet cells are large and numerous
• muscularis externa is unique, with 3 taenia coli dividing outer longitudinal smooth muscle
• -thin layer of longitudinal smooth muscle between bands, that “pucker” colon into haustra
• transverse/sigmoid colon has serosa, but ascending/descending, and cecum have adventitia

Question 21

structure of vermiform appendix

Answer 21

• epithelium resembles colon, but fewer and shorter crypts
• lamina propria has many lymphoid cells and lymph nodules that interrupt muscularis mucosa
• submucosa is frequently edematous
• muscularis externa has 2 complete thin layers, and no taenia coli
• serosa instead of adventitia

Question 22

what comprises the rectum?

Answer 22

upper rectum and anal canal

Question 23

structure of upper rectum

Answer 23

resembles colon, but no taenia coli, and less lymphoid tissue

Question 24

structure of anal canal

Answer 24

2. 5-4 cm long, and epithelium changes throughout
   - simple columnar epithelium –> stratified cuboidal –> stratified squamous nonkeratinized epithelium (ano-cutaneous area)
   - crypts and muscularis mucosa disappear
   - apocrine sweat glands (circumanal glands) present
   - inner layer of smooth muscle forms internal anal sphincter
   - outer longitudinal muscular externa becomes skeletal muscle for external anal sphincter