ELECTRON MICROSCOPY 



plasmic anastomoses between smooth muscle 

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 (1959). 



Stereocilia 



Rhodin, J., "Ciliated epithelia," Int. Rev. Cytol., 

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Striated Muscle 



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Tonofilaments 



Selby, C. C, "An electron microscope study of 

 the epidermis of mammalian skin in thin sec- 

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 (1955). 



Odland, G. F., "The fine structure of the inter- 

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Johannes A. G. Rhodin 



CILIATED EPITHELIA ULTRASTRUCTURE 



Ciliated epithelia are so called because 

 many of the cells which form the epithelial 

 layer are provided with a great number of 

 small motile structures on their surface — the 

 cilia. The ciliated epithelia are found in con- 

 nection with organs and tissues where a sur- 

 face has to be kept clean and moist, as in 

 the respiratory tract (nose, trachea, bronchi), 

 or in small ducts where a certain propulsion 

 of the content of the duct is facilitated and 

 aided by the beating of the cilia as in the 

 male reproductive tract (efferent ducts of 

 testis) and in the female reproductive tract 

 (oviduct). 



Function 



The ciliated epithelium in mammals is 

 characterized by several cell types (Fig. 8) 



the most prominent of which is the cili- 

 ated cell. The other cells have been classi- 

 fied as tion-ciliated cells which comprise 

 secretory cells of two types {serous and mucous 

 or goblet cells), the brush cells and the hasal 

 cells. The functions of the different cells de- 

 pend on the location of each cell. The goblet 

 cell is predominant in all ciliated epithelia 

 and keeps the surface moist by discharging 

 continuously a more or less viscous mucin. 

 The secretion product of the serous cells 

 either dilutes the mucin and/or adds en- 

 zymes (activators) to the content of the 

 ducts. The brush cells, presumably young 

 cells which have migrated from the basal 

 portions of the epitheliimi, are primarily the 

 precursors of the ciliated cells. They may 

 probably also be transformed into mucous 

 cells as well as serous cells. The appear- 

 ance of the brush cells of the efferent ducts 

 of the testis indicates that their function 

 here is mainly a secretory one. However, 

 certain structural features speak for the 

 fact that they also have absorptive functions. 

 The ciliated cells with their abimdant sur- 

 face extensions, the cilia, participate in 

 keeping the mucus blanket moving. The 

 ciliary beat is rather complicated. It is com- 

 posed of a rapid forward stroke and a slow 

 backward stroke. The cilium is rigid and 

 erected during the forward stroke, whereas 

 it folds itself beneath the mucus in a limb 

 and yielding movement during the backward 

 stroke. The activity of the cilia is syn- 

 chronized in local areas and moveinents of 

 the cilia over larger areas have been com- 

 pared with the appearance of a rye field 

 when the wind blows across it. The basal 

 cells are presumably the precursors of all 

 the cells of the ciliated epitheUa. The mitotic 

 activity among these cells is high and they 

 migrate to the upper portions of the epi- 

 thelial layer in order to replace ciliated or 

 serous cells when they are sloughed off and 

 lost in the moving mucus blanket. 



116 



