Stereology of human fetal adrenal medulla.

Stereological studies were performed on 27 pairs of adrenal glands of human fetuses (9-38 weeks of intra-uterine development). Medullary chromaffin cells were identified by immunostaining for chromogranin-A. The volume of adrenal medulla, average cell volume, and the number of chromaffin cells were calculated. The volume of adrenal medulla increased slowly up to the 20th week and afterwards it enlarged rapidly to the 31 st week of the fetal period. A gradual, linear increase in the number of chromaffin cells of developing adrenal medulla was observed during the studied period. On the contrary, the average volume of the adrenal medullary cells remained quite constant until the 17th week of the development. Afterwards, a gradual, linear increase in the cell volume was observed until the 31 st week, reaching a plateau by the end of intra-uterine development.