- Adrenal cortex
- Origin: Intermediate mesoderm, specifically from coelomic epithelium near the urogenital ridge
- Development:
- Around week 5–6, mesothelial cells near the root of the dorsal mesentery proliferate and invade underlying mesenchyme to form the fetal adrenal cortex (primitive cortex).
- A second wave of cells surrounds this and forms the definitive cortex, which later differentiates into the three adult zones:
- Zona glomerulosa – mineralocorticoids
- Zona fasciculata – glucocorticoids
- Zona reticularis – androgens
- The fetal cortex is large and produces steroids (especially DHEA) that are converted by the placenta into estrogens for pregnancy maintenance; it regresses after birth.
- Adrenal medulla
- Origin: Neural crest cells (from ectoderm)
- Development:
- Neural crest cells migrate medially and invade the medial aspect of the developing cortex.
- They differentiate into chromaffin cells, which are modified postganglionic sympathetic neurons that secrete catecholamines (adrenaline and noradrenaline).