Final answer:
The number of oocytes in the ovaries changes throughout development, declining from one to two million in an infant to zero at menopause. Oogenesis begins before birth and is arrested until puberty. The oocytes undergo development and growth in ovarian follicles during the ovarian cycle.
Step-by-step explanation:
The number of oocytes present in the ovaries changes throughout development. In a female infant at birth, there are one to two million oocytes. This number declines throughout life, reaching approximately 400,000 at puberty and eventually zero by the end of menopause. Oogenesis, which is the production of female gametes, begins before birth, and the oocytes are arrested in the meiosis I stage until puberty.
During the ovarian cycle, the oocytes undergo development and growth in ovarian follicles, a process called folliculogenesis. This typically leads to the ovulation of one follicle approximately every 28 days, with the oocyte inside the follicle remaining as a primary oocyte until right before ovulation. The death of ovarian follicles, known as atresia, can occur at any point during follicular development.
It is important to note that oogenesis produces up to four cells, but only one survives, as the cytoplasm is divided unequally during cell division.