112 VITAMINS A AND CAROTENES 



d. Geniiourinary Tract 



Keratinizing metaplasia in all species occurs in the renal pelvis, ureters, 

 bladder, epididjonis, uterus (see Fig. 27), oviduct, and accessory sex glands 

 in all species. Obstruction of the urinary system, the result of the accumu- 

 lation of keratinized cells, may be the immediate cause of death in rats, 

 and grossly visible lesions of this character have been found in human in- 

 fants.^' ^^ Other demonstrated sites of keratinizing metaplasia in the human 

 are uterus, epididymis. Fallopian tube, bladder, and vagina. In the urinary 

 tract desquamated keratinized cells may become the nidus of calculus 

 formation, but otherwise there is no direct relation of \itamin A deficiency 

 to calculus formation. Atrophy of the seminiferous tul)ules is also a result 

 of vitamin A deficiency in man and laboratory animals, but keratinizing 

 metaplasia does not occur. The undifferentiated sex cells — spermatogonia — 

 remain viable so that the atrophy, unlike that in vitamin E deficiency, is 

 reversible.*^' ^^' ^'" 



No effect of vitamin A upon the ovaries and/or ova has been described. 

 None has been found in human infants or in laboratory animals by the writer. 



e. Hematopoietic System 



No specific features have been described in man or hiboratory animals in 

 relation to the anemia, the atrophy of blood-forming bone marrow, and 

 the atrophy of lymphoid tissues — spleen, lymph nodes, and thymus. There 

 is, however, a greater deposit of hemosiderin in liver and spleen than that 

 which accompanies other vitamin deficiencies. The Hassall corpuscles of the 

 thymus become enlarged and distended with keratinized epithelial cells. In 

 animals, following the outburst of hematopoiesis in l)one marrow and spleen 

 produced by resumption of vitamin A feeding, the hemosiderin rapidly dis- 

 appears. 



/. Skin 



The conspicuous hyperkeratosis of hair follicles reported chiefly from 

 China^"' ^^ but also from other countries'* rarely appears before puberty in 

 vitamin A-deficient humans. With it is associated atrophy and hyperkerati- 

 nization of sebaceous glands and ducts of sweat glands. Although large 

 amounts of vitamin A unquestionably cause restoration to normal, the 

 precise relation of the hair follicle hyperkeratosis to vitamin A is confused 



Hyperkeratotic papules of hair follicle origin occui' in scm^'V of adults'^ 



'• K. E. Mason, J. Expll. Zoul. 55, 101 (1930). 



'2M. M. Sampson and V. Korcnchevsky, ./. Pathol. Biiclrriol. 35, 875 (1932). 

 13 C. N. Frazier and C. K. Hu, Arcli. Dermatol, and Syphilol. 33, 825 (1936). 

 1' O. A. Bessey and S. B. Wolhach, The Vitamins, Cliaptor 11, p. 27. American Med- 

 ical Association, ChicM^o, HI., 1939. 



