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Fig. 1 | Environmental Health

Fig. 1

From: Environmental pollutants, a possible etiology for premature ovarian insufficiency: a narrative review of animal and human data

Fig. 1

The different mechanisms inducing POI. Folliculogenesis (❶) begins after assembly (black arrows) of primordial follicles during second trimester of pregnancy. Activation of primordial follicles (green color) to enter the growth phase of folliculogenesis is continuous from third trimester of fetal life to menopause. This activation is driven by local factors and is independent of gonadotropins. Basal follicular growth (pink color) is driven by paracrine factors. From the early antral follicle stage, their growth depends on gonadotrophins to enter the final phase (orange color) up to ovulation. From the beginning, follicles undergo physiological atresia (blue lines around arrows), that participate to the decrease of the pool with years. Mechanisms leading to POI (symbolized by a final pale preovulatory follicle,): • decrease of the pool of primordial follicles (❺) either due to massive atresia (❺a) or default in assembly (❺b). • increase in follicular apoptosis concerning any other follicular stage (❷ and ❸). • increase of the activation (large green arrow) of the resting pool of primordial follicles (❹) resulting in its exhaustion. It is generally followed by increased atresia at following follicular stages (large blue arrow). • default in basal follicular growth leading to its arrest before the antral stages preventing ovulation while the pool of primordial follicles is normal (❻)

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