Fig. 20. Diagram of the structure and function heterogeneity of the granulosa cells in a healthy graafian follicle. The relative position of a granulosa cell in the cellular mass determines its proliferation and differentiation potential. (From Erickson GF: The graafian follicle: A functional definition. In Adashi EY (ed): Ovulation: Evolving Scientific and Clinical Concepts. New York: Springer-Verlag, 2000.)