GI Tract II Flashcards
1
Q
Length and segments of the small intestine
A
- 6 meters long
- Duodenum: 25cm
- Jejunum: 2.5m
- Ileum: 3.5m
2
Q
Major functions of the small intestine
A
- Move chyme
- Absorb nutrients
- Immunodefense
3
Q
What three structures increase the lumenal surface area of the small intestines, and by how much?
A
- Plicae circularis (valves of Kerckring): permanent transverse circular folds of mucosa/submucosa –> 2-3x increase
- Villi: finger-like projections of surface epithelium and lamina propria –> 10x increase
- Microvilli: projections of apical plasma membrane –> 20x increase
* Total surface area increase is 400-600 fold
4
Q
Crypts of Lieberkuhn
A
- Intestinal glands
- Simple tubular glands that extend from epithelium down to the muscular mucosae
5
Q
6 major cell types in the epithelium
A
- Absorptive cell (enterocyte)
- Goblet cell
- Enteroendocrine cell
- Paneth cell
- Stem cell
- M (microfold) cell
6
Q
Absorptive cells
A
- Tall columnar cells with striated border
- Microvilli: 1 micron tall, 0.1 micron diameter
- Secrete disaccharidases and peptidases - bind microvilli and produce monosaccharides and amino acids for absorption
- Lipids absorbed, reesterified to TG, converted to chylomicrons, released from lateral surfaces in lamina propria, absorbed by central lacterals
7
Q
Goblet cells
A
- Unicellular glands
- Produce acid glycoproteins (mucin type) –> lubricate and protect small intestine
- Less abundant in duodenum, increase towards ileum
8
Q
Enteroendocrine cells
A
- Unicellular glands
- Synthesize hormones and vasoactive peptides
- Most occur in the basal portion of the crypts of Lieberkuhn
9
Q
Paneth cells
A
- Exocrine cells
- Found in small groups at base of crypts
- Replaced every 30 days
- Apical cytoplasm filled with large, eosinophilic granules (lysozyme with antibacterial activity, controls intestinal flora)
10
Q
Stem cells in the small intestine
A
- Located near the base of crypts
- Move upwards repopulating the crypts and villi in 3 to 6 days
11
Q
M (microfold) cells
A
- Only found in ileum
- Specialized epithelial cells, cover Peyer’s patches
- Discontinuous basement membrane
12
Q
Gut-associated lymphoid tissue (GALT)
A
- Prominent in lamina propria of the small intestine
- 25% of mucosa
- Peyer’s patches: in ileum, groups of 20-40 lymphatic nodules covered by M cells –> take up antigens and deliver to lymphocytes in Peyer’s. IgA syn. by plasma cells
- Secretory component: glycoprotein made by absorptive cells, inserted in membrane. IgA dimers bind –> enter by endocytosis –. exit apical PM with SC bound, forming sIgA
- sIga binds antigens, toxins, microorganisms; *major role in host defense
13
Q
Brunner’s glands
A
- In submucosa of duodenum
- Mostly mucous type, secrete and alkaline mucous that helps protect against stomach acid and provides optimum pH for pancreatic enzymes
14
Q
Regional differences between duodenum, jejunum, and ileum
A
- Duodenum: Brunner’s glands in submucosa, adventitia, villi are squared off (resemble thick cactus leaves)
- Jejunum: Most highly developed plicae circularis, villi are longer/more finger-like than duodenum, more goblet cells, has serosa
- Ileum: longest villi, highest number of goblet cells, *Peyer’s patches (unique to ileum)
15
Q
Five gross subdivisions of the large intestine
A
- Colon
- Cecum (don’t need to distinguish)
- Appendix
- Rectum
- Anal canal
