Flashcards in Unit 6 - GI II Deck (24)
how is lumenal surface area increased in the small intestine?
1. plicae circularis (valves of Kerckring); 2-3x
2. villi (10x)
3. microvilli (20x)
what are plicae circularis?
valves of Kerckring; permanent transverse circular folds of mucosa and submucosa in SI only that increase SA 2-3 times
-most developed in jejunum
what are villi VS microvilli?
villi are projections on the surface of epithelium and lamina propria
microvilli are projections of apical plasma membranes
how do villi structure progress down the intestines?
-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))
what are the 6 major types of cells in the epithelium?
1. absorptive cell (enterocyte)
2. goblet cell
3. enteroendocrine cell
4. paneth cell
5. stem cell
6. M (microfold) cell
structure of and location of absorptive cells (enterocytes)
-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
structure of and location of goblet cells
-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
structure of and location of enteroendocrine cells
-unicellular glands that make hormones and vasoactive peptides
-in SI, most occur in basal part of crypts of Lieberkuhn
structure of and location of paneth cells
-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
what disease are paneth cells associated with?
-Paneth cells may be a site of origin for intestinal inflammation
structure of and location of stem cells
-located near base of crypts
-move upwards to repopulate crypts and villi in 3-6 days, and paneth cells every 30 days
structure of and location of M(icrofold) cells
-only in ileum
-specialized epithelium cells that cover Peyer's patches
-basement membrane under M cells is discontinuous
what is GALT? where is it? what are its components?
makes up 25% of mucosa
-prominent in lamina propria of SI
how are Peyer's patches associated with GALT?
-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
how is IgA associated with GALT?
synthesized by plasma cells in Peyer's patches
how is secretory component associated with GALT??
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
what are some regional differences in the SI for duodenum?
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)
what are some regional differences in the SI for jejunum?
-most highly developed plicae circularis
-villi are longer and more finger like than in duodenum
-more goblet cells
-has serosa, not adventitia
what are some regional differences in the SI for ileum
-longest villi and highest number of goblet cells
-Peyer's patches unique to ileum
structure of colon and cecum
-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
structure of vermiform appendix
-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
what comprises the rectum?
upper rectum and anal canal
structure of upper rectum
resembles colon, but no taenia coli, and less lymphoid tissue