million)are present at birth; no more are produced afterwards. The ovarian cycle consists of one of the several follicles developing into a primary follicle, then Graafian follicle, then a corpus luteum under the influences of FSH and LH. Ovulation is triggered by a powerful surge of gonadotrophins. The ovarian cycle is"shadowed"by the menstrual cycle during which the uterine endometrium is firstly proliferative(due to estrogen) then secretory(due to estrogen and progesterone). Decline in progesterone and estrogen when the corpus luteum degenerates precipitates a menstruation. Pregnancy is the period from conception to birth. After the egg is fertilized by a sperm and then implanted in the lining of the uterus, it develops into the placenta and embryo, and later into a fetus. Only I per 100,000 sperm of the 200-400 million contained in the 3-4 ml of the ejaculate deposited near the cervix, where capacitation takes place, reach the fallopian tubes where fertilization ideally occurs. Enzymes from the acrosomes of the many sperm digest the ntercellular cement between the cumulus cells, allowing a single sperm to penetrate. On penetration by the first sperm, the ovum becomes impervious to other sperm. a second polar body is released, About 6 days after fertilization, the zygote(now a blastocyst)implants, The placenta takes over the production of estrogen and progesterone from the corpus luteum after the first trimester of the pregnancy. Placenta progesterone inhibits inappropriate contractions of the myometrium. Labor is divided into three phases: from onset of contractions to full dilatation of the cervix @to delivery of the fetus; the expulsion of the placentamillion) are present at birth; no more are produced afterwards. The ovarian cycle consists of one of the several follicles developing into a primary follicle, then Graafian follicle, then a corpus luteum under the influences of FSH and LH. Ovulation is triggered by a powerful surge of gonadotrophins. The ovarian cycle is "shadowed" by the menstrual cycle during which the uterine endometrium is firstly proliferative (due to estrogen) then secretory (due to estrogen and progesterone). Decline in progesterone and estrogen when the corpus luteum degenerates precipitates a menstruation. Pregnancy is the period from conception to birth. After the egg is fertilized by a sperm and then implanted in the lining of the uterus, it develops into the placenta and embryo, and later into a fetus.Only 1 per 100,000 sperm of the 200~400 million contained in the 3~4 ml of the ejaculate deposited near the cervix, where capacitation takes place, reach the fallopian tubes where fertilization ideally occurs. Enzymes from the acrosomes of the many sperm digest the intercellular cement between the cumulus cells, allowing a single sperm to penetrate. On penetration by the first sperm, the ovum becomes impervious to other sperm. A second polar body is released. About 6 days after fertilization, the zygote (now a blastocyst) implants. The placenta takes over the production of estrogen and progesterone from the corpus luteum after the first trimester of the pregnancy. Placenta progesterone inhibits inappropriate contractions of the myometrium. Labor is divided into three phases: ①from onset of contractions to full dilatation of the cervix; ②to delivery of the fetus; ③the expulsion of the placenta. 5