1 - The Structure of the Mammalian Adrenal Cortex

Abstract

This chapter discusses the problems of adrenocortical structure using histochemical and ultrastructural techniques. In embryological development, adrenocortical cells arise from mesoderm, particularly from the columnar epithelial cells that line the coelom. Chromaffin cells have a separate origin, coming from neighboring paraganglion cells of the neural crest complex and thence migrating to lie adjacent to cortical cells. This intermingling is characteristic of most submammalian vertebrates though Elasmobranchii display complete separation. In Mammalia, the adult adrenal gland shows coalescence of chromaffin tissue and in Eutheria and Metatheria it lies centrally and is termed the medulla and eccentrically in the Prototheria. It is only over the past 10 years that the role of organelles in the biosynthesis of steroid hormones has begun to be delineated with correlated changes in fine structure. Changes occur in the smooth endoplasmic reticulum—the surface of which increases in area when the rate of steroidogenesis rises— and the mitochondrial cristae, which are usually tubular or vesicular in steroid secreting cells. Lamelliform cristae differentiate into tubular then vesicular cristae in most species studied. This is related to adrenocortical stimulation, for example, by ACTH. Thus, in hypophysectomized animals, the predominant tubular type is changed to vesicular by the administration of ACTH.