Primordial Follicle

Abstract

Primordial oocytes in the ovary of human and nonhuman primates and other mammalian species remain in an arrested meiotic prophase for a long time in the cortex (Fig. 1) until advanced stages of follicle recruitment when they resume maturation, preliminary to either ovulation or atretic regression (Zamboni 1972,1974,1976,1980, Guraya 1970a, 1974a, Amin et al. 1976, Bjërsing 1978, Dvořák and Tesařík 1980). They are separated from one another by a thick connective tissue stroma (Fig. 1) consisting of fibroblasts, blood vessels and bundles of collagen and reticular fibres. Primordial follicle appears as a relatively simple structure consisting of a centrally located oocyte with a single layer of granulosa cells, demarcated by an all- encompassing basal lamina which separates it from the surrounding stroma (Fig. 2). Follicles remain in this condition of simple structural organization until the time they regress (atresia), or undergo the maturation process that eventually results in ovulation and liberation of mature and fertilizable eggs. This meiotic arrest is believed to be actively maintained by the inhibitory effect of follicle cells on oocyte maturation (Edwards et al. 1977). The primordial follicles lie close to the surface epithelium and have no independent blood supply. During the period of sexual maturity primordial follicles and growing follicles, in various stages of their development and differentiation, and atretic follicles lie next to one another (Fig. 3), and their morphological (including ultrastructural) histochemical and biochemical features have been studied.