Upper panel shows a typical zonula occludens of rat intestinal epithelium, prepared using freeze fracture techniques. A network of intersecting strands on the P-face, and a complementary pattern of grooves on the E-face of this freeze fracture image. The lower panel includes a portion of a Sertoli junction from human testis consisting of a large number of parallel rows of complementary grooves of intramembranous particles which adhere preferentially to the E-face. Fig. 70 micrograph (upper) contributed by J.P. Revel; fig. 71 (lower) from Suzuki and Nagano, Cell Tissue Res. 166: 37 (1976), reprinted with permission in Chapter 3 (Junctional Specializations) of 'The Cell, 2nd Ed.' by Don W. Fawcett M.D. A PDF copy of the accompanying chapter is available on the ASCB's BioEDUCATE website.