HYPOVITAMINOSIS A (aVITAMINOSIS a) 595 



Tissues and on Organs. The effects of vitamin A deficiency are similar, 

 irrespective of whether the epithehum is of ectodermal, mesodermal, or 

 entodermal origin. In all cases, atrophy occurs, a reparative proliferation 

 by the basal cells follows, and growth and differentiation of new cells into 

 a stratified keratinizing epithelium take place. The replacement of 

 epithelium, regardless of the site of damage and of its original fimction, is 

 identical everywhere, and is comparable to the layers of the epider- 

 jj^lg 1026,1027,1040 When vitamin A is given, the morphologic structure of the 

 tissue returns to normal in each area, and normal function is resumed. ^"''^ 



The sequence in which the organic deficiency symptoms appear varies 

 somewhat with species, but the same organs are usually invoh-ed. The 

 epithe lia which atrophy and which become replaced by stratified keratinizing 

 epithelia are those which possess the function of secretion, in addition to 

 acting as a covering layer. These functioning cells are not capable of 

 division. The order of appearance of keratinizing metaplasia, according 

 to Wolbach,'''^'^ is as follows in man as well as in animals: salivary glands, 

 including submaxillary, parotid, and all the accessory buccal glands of the 

 mouth, tongue, and pharynx; the respiratory tract, together with the nares 

 and accessory shiuses; Jacobson's organ, the trachea and bronchi; the 

 genitourinary tract, including the bladder, ureter, renal pelvis, epididymis, 

 prostate, seminal vesicles, coagulating gland, uterus, oviduct, and acces- 

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

 the corneal and palpebral conjunctivae, the Harderian, intraorbital and 

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



a'. Effect on the Eyes: The effects of vitamin A deficiency on both the 

 internal functioning and the external structure of the eye are evident. In 

 the first case, night blindness is a result of vitamin A deprivation, but there 

 are no demonstrable moiphologic changes in the retina. ^"-^ The condition 

 is reversible in the adult. On the other hand, when irreversible loss of 

 vision does occur in young animals deprived of vitamin A, it may be traced 

 to the effect of pressure on the blood vessels and optic nerve due to the re- 

 tardation in growth of the skull. ^"^^ According to Johnson, '"^^ when 

 twenty-three-day-old rats were placed on a vitamin A-free diet, edema of 

 the retina was the first s^Tnptom. This was followed by slight degenera- 

 tive changes of the outer segments of the rods. When vitamin A was 

 given, the normal condition was rapidly restored. Following prolonged 

 deprivation of vitamin A, more profound degeneration of the outer seg- 



io« S. B. Wolbach and O. A. Bessey, Physiol. Revs., 22, 233-289 (1942). 

 '»4i S. B. Wolbach and P. R. Howe, ./. Exptl. Med., 57, 511-526 (1933). 

 i"" M. L. Johnson, Arch. Ophthalmol. {Chicago), 29, 793-810 (1943). 



