However, recent work suggests that adrenocortical cells arise within or underneath the capsule under the influence of sonic hedghog signalling and move centripedally along gradients towards the border to the adrenal medulla where they form cortical islets and / or undergo apoptosis (1,3,4). In some rat species, a fourth zone can further be distinguished, the zona intermedia, between the glomerulosa and the fasciculata currently postulated to be a site of initiation of adrenocyte proliferation and differentiation and a zone containing the adrenal cortical stem cells. The latter zone contains cells morphologically identical to zona fasciculata cells, as well as a smaller cell type. Zona glomerulosa cells are round and smaller than the polyhedral cells of the zona fasciculata, which gradually extend into the zona reticularis. The inner zona reticularis, site of adrenal androgen (predominantly dehydroepiandrostenedione, DHEA sulfate and androstenedione) secretion, as well as some glucocorticoid production (cortisol and corticosterone).Īdrenocortical cells are arranged in a cord-like manner, extending from the adrenal capsule to the medulla, and are embedded within a widespread capillary network. A number of factor were described to be essential for adrenal development on a molecular level, among them steroidogenic factor-1, CITED-2, β-catenin, and others (1,2). The development of the adrenal cortex is dependent on blood supply, paracrine adrenal factors, hormonal factors, and adrenocortical innervation. In contrast, the definitive adult cortex arises from cellular hyperplasia associated with decreased apoptosis. After birth, shrinkage of the fetal zone due to increased apoptotic activity occurs. The human fetal adrenal cortex consists of two parts, the fetal and the definitive adult zones.

In later stages of embryonic development, the cortex engulfs, and ultimately encapsulates the entire medulla. At 7 weeks of gestation, sympatho-adrenal cells migrate into the adrenal primordium. This tissue gives rise to the fetal adrenal cortex and to Lyedig cells. An isolated clump of cells appears within the urogenital ridge, known as the adrenal-gonadal primordium.

The adrenal gland is composed of two embryologically distinct tissues, the cortex and medulla, arising from the mesoderm and neuroectoderm, respectively.

Medulla hormones