Primordial Follicle

Definition - What does Primordial Follicle mean?

A primordial follicle is the most immature form of an egg. The primordial follicle consists of an egg cell (oocyte) that is surrounded by a single layer of thin, flat epithelial cells that protect the egg as it waits for signals to begin development and maturation. All primordial follicles are present at birth, and throughout the lifespan, primordial follicles always make up the majority of follicles found in the ovary.

FertilitySmarts explains Primordial Follicle

All eggs available for reproduction throughout a woman's lifespan are present in the ovaries at birth in the form of primordial follicles. These primordial follicles begin to develop prenatally in humans around 20 weeks gestation. Formation of the primordial follicle occurs in the initial stage of folliculogenesis, which is the process of egg formation and maturation. A single layer of epithelial cells envelope the egg as acts as a shield from neighboring cells and hormonal fluctuations.

Further development of primordial follicles can happen sporadically between birth and puberty. During puberty when a regal menstrual cycle develops, primordial follicles are directed by the sex hormones estrogen and progesterone to develop and mature further in preparation for ovulation. With each menstrual cycle, a new primordial follicle is recruited for this process. As a woman approaches menopause her reserve of primordial follicles becomes depleted and eggs are no longer available for reproduction. If the reserve of primordial follicles is depleted significantly earlier than the average age of menopause a woman may be experiencing a condition known as premature ovarian failure (POF) which indicated a general decrease in fertility.

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