The production of mature egg cells (ova – see OVUM) by the OVARIES. Germ cells in the ovary multiply to produce oogonia which divide by MEIOSIS to form oöcytes in the FETUS.
n. the process by which mature ova (egg cells) are produced in the ovary (see illustration). Primordial germ cells multiply to form *oogonia, which start their first meiotic division to become *oocytes in the fetus. This division is not completed until each oocyte is ovulated. The second division is only completed on fertilization. Each meiotic division is unequal, so that one large ovum is produced with a much smaller polar body.
n. the process by which spermatozoa and ova are formed. In both sexes the precursor cells undergo *meiosis, which halves the number of chromosomes. However, the timing of events and the size and number of gametes produced are very different in the male and female. See oogenesis; spermatogenesis.... gametogenesis
n. the main female reproductive organ, which produces ova (egg cells) and steroid hormones in a regular cycle (see menstrual cycle) in response to hormones (*gonadotrophins) from the anterior pituitary gland. There are two ovaries, situated in the lower abdomen, one on each side of the uterus (see reproductive system). Each ovary contains numerous follicles, within which the ova develop (see illustration), but only a small proportion of them reach maturity (see Graafian follicle; oogenesis). The follicles secrete *oestrogen and small amounts of androgen. After ovulation a *corpus luteum forms at the site of the ruptured follicle and secretes progesterone. Oestrogen and progesterone regulate the changes in the uterus throughout the menstrual cycle and pregnancy. —ovarian adj.... ovary
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