Ovulatory changes in the wall at the apex of the human Graafian follicle.

The apical wall was studied ultrastructurally in 16 human follicles at various stages of development. In the theca externa and tunica albuginea at the apex of growing follicles, fibroblasts with little cytoplasm and abundant collagen fibres were observed. In the mature follicles, the fibroblastic cytoplasm was well developed, rich in lysosome-like granules and contained peripheral multivesicular structures. Intercellular collagen fibres were sparse. It is suggested that the collagen fibres are digested by the content of lysosomal granules and multivesicular structures, thus aiding follicular rupture.