46 



EPITHELIAL TISSUES 



It will assist in the understanding of the structure and morphological 

 characteristics of the several layers of cells to think of the superficial 

 a squamous cells in terms of the innermost 



columnar cells, modified during the pas- 

 sage to the surface by mechanical (pres- 

 sure), physical (desiccation), and chem- 

 ical (keratization) factors. 



2. PSEUDO-STRATIFIED COLUMNAR 

 EPITHELIUM 



FlG. 51. P S E U D O - STRATIFIED 

 COLUMNAR CILIATED EPITHE- 

 LIUM FROM A BRONCHIAL TUBE 



OF MAN. 



a, a goblet cell; 6, cilia; c, super- 

 ficial cytoplasmic layer; d, deeper 

 nucleated layer, the nuclei of the 

 columnar cells are somewhat more 

 deeply stained than those of the 

 basal cells; e, basement mem- 

 brane; /, connective tissue. Hema- 

 tein and eosin. X 550. 



The superficial cells only of this va- 

 riety of epithelium are columnar in 

 shape, and except in one or two unim- 

 portant places are always ciliated. The 

 deeper extremities of these columnar 

 cells taper to a point, and extend all the 

 way to the basement membrane. Be- 

 tween the tapering ends of these cells 

 small spindle-shaped and spheroidal cells 

 are closely packed. The several varieties 

 of cells thus appear to be superimposed, though 

 all actually rest upon the basement membrane. 

 The 'superficial' cells of this variety extend 

 throughout the entire thickness of the mem- 

 brane. Hence this form of epithelium may in 

 one sense be called 'simple' rather than 'strat- 

 ified.' The distribution of this variety of the 

 epithelium is practically identical with that of 

 ciliated cells. The deeper extremities of the 

 columnar cells are occasionally bifid or even 

 somewhat varicose in order the more closely to 

 fit between the spindle-shaped and spheroidal 

 cells of the deeper portion. The nucleus of these 

 latter cells is usually situated a little below the 

 middle of the columnar cell, so that all the nuclei 

 of the epithelial membrane lie within its deeper 

 half, thus giving to this portion a more deeply 

 chromatic appearance when observed in stained sections under low mag- 

 nification. The superficial half of the epithelial layer contains only 



FIG. 52. DIAGRAM 

 SHOWING THE MAN- 

 NER IN WHICH ALL 

 THE EPITHELIAL 

 CELLS OF PSEUDO- 

 STRATIFIED CILIATED 

 EPITHELIUM REACH 

 THE BASEMENT MEM- 

 BRANE. 



Letters as in the pre- 

 ceding figure. 



