BIOC21 - EPITHELIUM (near verbatim + diagrams).doc

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University of Toronto Scarborough
Biological Sciences
Stefan Rusyniak

EPITHELIUM: Lec 2 Fig 1. Fig 2. Body composed of water mostly. When tight junctions (occludens barrier) are broken, water moves into lumen = diarrhea. Surface Specializations: 1) Microvilli: • Short projections at surface of epithelial cell • Increases surface area (SA) by 30X • Absorption • 1-2 micrometers long (short) • can’t discern individual microvilli under light microscope (resolution: 0.2 micrometers = 200 nm)  lot of microvilli = thicker apical boundary = dbl line = brush border • b/c microvilli = made of lots of cytoskeletal proteins, absorbs bit of light = therefore seen as dark 2) Stereocilia: • Similar in molecular way (cytoskeleton structure) to microvilli but much longer (= 100 micrometer = very long) • Stereovilli • Not found in many places • Inner ear = detect sound, mvt (sensory • Absorptive fx also in ductus epididymus 3) Cilia: • Found in places where you have to move things along surface • Trachea (beats mucus upwards), Fallopian tubes • 10 micrometers 4) Glycocalyx: • Molecular structure = complex carbs attached to membrane lipids/proteins (glycolipids/proteins) • Highly branched • PAS = red stain precipitate 4 carbs; usually don’t see it on surface of cell b/c poorly stained/not thick • But in some parts of body, it is thick/elaborate = areas of absorption • Small intestine, carbs on microvilli, spread out in lumen • Reason 4 glycocalyx not really well understood, maybe: i. Bushy glycocalyx at surface would slow things down at surface = good 4 absorption, interact 4 longer time = efficient = increase chance of interacting with appropriate transport mocs ii. Outer surface covering = glycocalyx = therefore more difficult 4
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