NON-STBATIFIED EPITHELIA 



39 



FIG. 43. CuBoroAL EPITHELIUM FROM THE 

 RETE TESTIS OF THE RABBIT. 



a, epithelium; b, connective tissue. Hema- 

 tein and eosin. X 550. 



2. SIMPLE COLUMNAR EPITHELIUM 

 (a) Plain 



This type of epithelium consists of columnar or cylindrical elements 

 (Fig. 39), in transverse section presenting polygonal, frequently hex- 

 agonal, outlines (Fig. 40). It 



may be tall, medium or low ^ ^ y * ^. JE ' ...O^ g^ . 



columnar epithelium, depend- 

 ing upon the height of the in- 

 dividual cell of .the particular 

 membrane. The lower types 

 may be designated cuboidal 

 epithelia (Fig. 43). The phe- 

 nomenon of polarity is partic- 

 ularly well exhibited by a tall 



columnar cell, a condition inhering in a structural and functional differ- 

 entiation between the attached, or 

 proximal, and the free, or distal, end 

 of the cell, dependent in a final an- 

 alysis in larger measure upon dis- 

 tance from source of the nutritive 

 and oxygenative stream in the blood. 

 The nucleus is generally located 

 nearer the proximal end; this end, 

 moreover, tapers to a point and is 

 occasionally bifid; and it contains 

 the presecretion (ergastoplasm, pro- 

 zymogen, etc.) granules, rodlets and 

 fibrils in secreting epithelia (Fig. 

 35). The distal border is frequently 

 striated (cuticular margin, striated 

 border, Fig. 38, b), an appearance 

 due to the presence of minute canals, 

 or more frequently, short pseudo- 

 podia, mediating absorption or the 

 elimination of secretion. Striated 

 borders are particularly prominent 

 in the columnar cells of the intes- 

 tine. In the secreting cells of the 



FlG. 44. TlP OF A VlLLUS OF THE 



SYNOVIAL MEMBRANE FROM THE 

 KNEE-JOINT OF AN OLD MAN. 

 The core contains capillaries em- 

 bedded in a compact, delicately fibrillar 

 stroma. A distinct basement mem- 

 brane appears in certain regions. The 

 epithelium is of the low columnar or 

 cuboidal type. 



