CHAPTER II 



EPITHELIAL TISSUES 



TISSUES 



A tissue in the histologic sense is a collection of similarly specialized 

 cells united in the performance of a particular function, e.g., liver tissue. 

 In certain tissues the cells are joined together by an intercellular cement 

 substance, e.g., epithelia, a secretion product of the cells themselves. 

 Through this cement may extend the so-called 'intercellular bridges' or 

 cytodesmata (Fig. 33), the minute intervening spaces forming delicate 





' - - ! --' -. *W T ^ F J*S ; J' 



'*&&^ ' 



FIG. 33. GROUP OF EPITHELIAL CELLS FROM THE MALPIGHIAN LAYER OF 



THE SKIN. 



The intercellular bridges are very distinct. Hematein and eosin. X 1,000. 



canaliculi, presumably for mediating the transfer of nutritive material 

 from cells more favorably placed with respect to the source of supply to 

 those less favorably located, e.g., epidermis; these bridges arise through 

 process of vacuolization in the exoplasm of adjoining cells, the walls 

 of the original vacuoles persisting as 'bridges/ Through such bridges, 

 fibrils may extend from cell to cell. Practically every tissue contains 



30 



