Two-dimensional diagram of a transverse section of the caudal region of a 6-week embryo. The fetal suprarenal cortex is derived from mesodermal cells. The medulla is formed from an adjacent sympathetic ganglion that is derived from neural crest cells. The diagram also shows the development of the gonads at this time (see Box 6.3)

After the neural crest cells have migrated they are engulfed by the fetal cortex and they differentiate into the secretory cells of the adrenal medulla. More mesodermal cells surround the fetal cortex and these will eventually form the permanent adult cortex.

At birth the adrenal gland is relatively much larger than the adult gland due to the extensive size of the fetal cortex. The zona glomerulosa and fasiculata are differentiated.

After 1 year the fetal cortex has all but disappeared but the zona reticularis is not recognizable until the end of the 3rd year after birth.