File:Epithelial junctions EM01.jpg

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Epithelial Junctions Electron Micrograph

Junctional complex between two cells in the epithelium of the intestinal mucosa (rat), intestinal lumen is towards the top of image. These 2 epithelial cells have a range of different junctional complexes along their lateral contact membranes. Half (hemi-) versions of these junctions also occur on the cell basal membrane where it attaches to the extracellular matrix (basal lamina, visible in EM), not shown in this image.

  • Tight junction - (zonula occludens), located nearest the lumen, extends from arrow 1 to arrow 2. The narrowing of the apparent intercellular "gap" (~90 A) is clearly visible, but the fusion line of the two apposed membranes cannot be clearly distin- guished at this magnification. Note that there is relatively little accumulation of dense cytoplasmic material along this part of the complex.
  • Adherens junction - (zonula adhaerens) intermediate junction extends from arrow 2 to arrow 3. A relatively wide intercellular space (~200 A) is maintained throughout the junction. Extensive condensation of cytoplasmic fibrils occurs as a fine feltwork along either side of the junction. This condensation is continuous with the terminal web (tw) into which the filamentous rootlets (r) of the microvilli penetrate. Plate-like densifications within the cytoplasmic feltwork can be seen along part of the junction, especially along the right side (pi).
  • Desmosome - marked by arrows 4 and 5. This element is characterized by a wide intercellular space (~240 A) bisected by an intermediate line (id). Bundles of cytoplasmic fibrils (fd), coarser (diameter ~80 A) and more distinct than those of the terminal web, converge into dense plates (pd) on each side of the desmo- some. These plates are separated from the inner leaflets of the cell membrane by a zone of low density. Similar fibrils (if) appear throughout the remainder of the field below the terminal web.

Between the intermediate junction and the desmosome, the two apposed cell membranes are separated by an irregular space of varying width and show membrane invaginations and associated vesicles (v). The trilaminar structure of the cell membrane (cm) shows clearly along the mlcrovilli (my), (wherever the membrane is sectioned normally), and within the desmosome. It can also be made out, though less regularly, along the lateral cell margins (e.g., at unnumbered arrow). Note that the luminal membrane is nearly symmetrical, the outer leaflet being only slightly thinner and less dense than the inner leaflet, whereas the lateral membrane is definitely asymmetrical. The total thickness of all three layers is about 110 A along the apical surface of the cell but measures only about 70 to 80 A along the lateral intercellular spaces. Note also the fluffy dense material (fro) (probably mucus) associated with the tips and sides of the microvilli.

Specimen fixed in 2 per cent OsO4 in acetate-Veronal buffer (pH 7.6) ; and embedded in Epon. Pb(OH)2-stained section. X 96,000. (Stain - Osmium)

(text modified from original figure legend)


A = angstrom or ångström 1×10−10 m

Adhesion EM Images: GIT epithelia EM1 | GIT epithelia EM2 | GIT epithelia EM3 | Desmosome EM
Adhesion Cartoons: Tight junction | Adherens Junction | Desmosome | Gap Junction

Reference

M G FARQUHAR, G E PALADE Junctional complexes in various epithelia. J. Cell Biol.: 1963, 17;375-412 PubMed 13944428

| PMC2106201 | JCB

Abstract

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