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Oocyte
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The oocyte is the female germ cell, that is, the cell the egg develops from. It does not float free: it lives inside a primordial follicle, a kind of microscopic case in which a single layer of granulosa cells surrounds it and feeds it.
The striking part is when it is made. Everything begins before birth, while the female fetus is still in the uterus. The germ cells finish multiplying by mitosis, the ordinary division of cells, and then enter meiosis, the special division of reproductive cells. And there they stop: they stay arrested in prophase I, the first stage of that division. A cell frozen halfway through a division.
Their number, moreover, goes in only one direction from that point on. Around week 20 of pregnancy there are 6 to 7 million germ cells; at birth 1 to 2 million primordial follicles are left; and by puberty 400,000 to 500,000 remain.
In brief
The oocyte is the female germ cell; it sits inside a primordial follicle, surrounded by a single layer of granulosa cells that nourish it.
It forms before birth: the germ cells finish their mitosis, enter meiosis and arrest in prophase I.
A cell frozen halfway through a division.
From week 20 onward their number only falls: 6 to 7 million germ cells, 1 to 2 million at birth and 400,000 to 500,000 at puberty.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingEmbryology, Ovarian Follicle Development, StatPearlsPublished
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