Histological Studies on X-Zone of Adrenal Cortex

Abstract

1. Foetal adrenal cortices of mice showed a striking sex-difference, marked aging-variety and some individual-difference in respective postnatal development (3rd-35th day after birth).2. In the 3rd postnatal day of both female and male mice, the abundant immature cells forming a germ of adult adrenal cortex occurred in the capsule or at its underlying area. They are presumably ensued from the fibroblasts. In advancing days, these immature cells were gradually differentiated and multiplied toward the medulla in bringing pressure on atrophic foetal cortices.3. An apparent boundary zone was not present between the innermost cortex and medulla in the 3rd day, but the foetal cells invaded the interlobular tissues of medulla, where were present a mass of atrophic and degenerating cells and the hyperamic sinusoids.4. In both sexes the parallel chang wase demonstrated between the involution of foetal cortex and the neoformation of adult cortex from 6th to the the 9th day; the latter may bring presure on the former to transmigrate inward. However after the 9th day the sex-differences appeared: In males, as the adult cortex rapidly grew on, the foetal cortex fell into an involulion, which was concrete in the 30th day, followed by the proliferetion of connective tissue enclosing the medulla. While in females, the development of adult cortex was slack and foetal one thichened co-existed with the former in the 20th day.5. In the 25th-30th day, foetal cortex was hypertrophic, whose constituent cells were arranged fascicularly, probably involving in the independent functional significance. The cytoplasm of these cells was pale and enlarged, containing a few fat granules, but abundant mitochondria. Thus both kinds of foetal and adult cortices were capable to be distinguished from one another at the remarks on the cell distribution and their internal structures. So far as the postnatal days of the animals are concerned (up to 35th day), the foetal cortex did not completely disappear in females. From above observation we came to a conclusion that X-Zone is nothing but vestiges of foetal cortex, and sholud be correctly different from the reticular zone of adult cortex.