Читать книгу Human Developmental Biology - Danton Inc. O'Day - Страница 19

The number of “eggs” in the human ovary changes dramatically over time as shown in Figure 3.5. The presented data was produced by analyzing many sections of ovaries from females of different ages after autopsy. The final “actual” numbers were calculated from these counts and used to generate this graph. It should be noted that since the numbers were generated from fixed ovarian sections, the term “eggs” refers to all stages of oogenesis not just mature eggs. In short it reflects the reproductive status of the ovary—the number of potential eggs that a female could produce at each stage of her life. As can be seen from the graph these changes in number are massive.

Figure 3.5. The changes in germ cell number in the female ovary.

Here’s what the graph reveals:

•The number of eggs increases to around 7 million by six months in utero.

•Then the number of eggs decreases due to apoptosis (controlled cell death).

•At birth approximately two million eggs remain.

•By the time of puberty onset only around half a million eggs are present.

•A continual decline occurs until menopause due to ovulation and egg death.