108 VITAMINS A AND CAROTENES 



The order of the deficiency responses of organs varies somewhat with 

 the species of animal, inchiding man, but the same organs are involved and 

 are presented here roughly in order of seciuence of appearance of keratinizing 

 metaplasia: salivary glands, including the submaxillary, parotid, and all 

 accessory glands of the buccal cavity, tongue, and pharynx; the respiratory 

 tract, including the nares and accessory sinuses; Jacobson's organ, trachea, 

 and bronchi; genitourinary tract, including the bladder, ureter, renal pelvis, 

 epididymis, prostate, seminal vesicles, coagulating gland, uterus, oviduct, 

 and accessory sex glands of the vulva; eyes and paraocular glands, including 



ns 



'^'\ 



*V 



Fig. 26. Vitamin A deficiency in the rat. Duct of the subinnxiUarv gland showing 

 a focus of reparative proliferation with early undermining and kei-atinizing meta- 

 plasia. 



the corneal and palpebral conjunctivae, the Hardei'ian, intraorbital and 

 extraorbital lacrymal glands, and the Meibomian glands; the skin. 



In general, in vitamin A deficiency, the epithelia which atrophy and which 

 become replaced l)y stratified keratinizing epithelium are those which have 

 a secreting function in acidition to the role of a co\'ering layer and whose 

 fiuictioning cells are without power to divide. lU'placement, therefore, takes 

 place from focally distrilnited basal cells which multiply, spread beneath 

 the original epitheliimi, and finally, through coalescence of areas thus pro- 

 duced and differentiation, foi'm a continuous epidermis-like layer (Figs. 26, 

 27, and 28). Epithelial cells with more complex physiological roles and power 

 to divide, such as liver, renal tubules, adrenals, and anterior hypophysis, 

 do not exhibit early severe atrophy, nor are they replaced In^ keratinizing 

 epithelium. The stratified and transitional epithelia — cornea, renal pelvis, 

 ureter, and bladder — become hyperkeratotic, all of the continuous layer of 

 basal cells participating in the i)r()cess. Presumably these ei)ith(^lia have 



