Follicle Development

Histologically, three basic types of ovarian follicles can be identified on the basis of developmental state:

• Primordial follicles

• Growing follicles

• Mature or Graafian follicles

Growing follicles are further subcategorized as primary and secondaiy (or antral) follicles. Some histologists identify additional stages in the continuum of follicular development. In the cycling ovary, follicles are found at all stages of development, but primordial follicles predominate.

The primordial follicle is the earliest stage of follicular development

Primordial follicles first appear in the ovaries during the third month of fetal development. Early growth of the primordial follicles is independent of gonadotropin stimulation. In the mature ovary, primordial follicles are found in the stroma of the cortex just beneath the tunica albugínea. A single layer of squamous follicle cells surrounds the oocyte (Fig. 22.3). The outer surface of the follicle cells is bounded by a basal lamina. At this stage, the oocyte and the surrounding follicle cells are closely apposed to one another. The oocyte in the follicle measures about 30 p,m in follicle cells basal lamina rER stromal mitochondrion

annulate lamellae

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