Instead of exerting a negative feedback on the pituitary, these hormones now exert a positive feedback, stimulating the pituitary to release FSH and large amounts of LH. LH then triggers the remaining follicle cells to differentiate into the corpus luteum, which secretes estrogen and progesterone. At the end of the cycle, if an embryo has not implanted, the corpus luteum degenerates.
When the corpus luteum degenerates, it no longer releases estrogen and progesterone. This hormone triggers the cells of the uterine lining to proliferate, and the lining becomes thicker. Afterward, the follicle cells remaining in the ovary develop into the corpus luteum, a structure that releases estrogen and progesterone.
The hormones maintain the uterine lining at a peak thickness and preparedness for embryo implantation. Without these hormones, the uterine lining also breaks down, initiating menses.
In addition to luteinizing hormone LH , follicle-stimulating hormone FSH , estrogen, and progesterone, there is yet another hormone that plays an important role in these cycles. Called gonadotropin-releasing hormone GnRH , this hormone is released from the hypothalamus. LH and FSH stimulate oocytes to develop and ovaries to release estrogen and progesterone. Estrogen and progesterone stimulate the development of the uterine lining. There are still eggs and potential follicles on the ovaries, but without the stimulation of FSH and LH, they will not produce a viable egg to be released.
The outcome of this is the inability to have children. The side effects of menopause include hot flashes, heavy sweating especially at night , headaches, some hair loss, muscle pain, vaginal dryness, insomnia, depression, weight gain, and mood swings.
Estrogen is involved in calcium metabolism and, without it, blood levels of calcium decrease. To replenish the blood, calcium is lost from bone which may decrease the bone density and lead to osteoporosis. Supplementation of estrogen in the form of hormone replacement therapy HRT can prevent bone loss, but the therapy can have negative side effects. While HRT is thought to give some protection from colon cancer, osteoporosis, heart disease, macular degeneration, and possibly depression, its negative side effects include increased risk of: stroke or heart attack, blood clots, breast cancer, ovarian cancer, endometrial cancer, gall bladder disease, and possibly dementia.
Improve this page Learn More. Skip to main content. Module The Reproductive System. Search for:. The Ovarian Cycle, the Menstrual Cycle, and Menopause Learning Outcomes Discuss the interplay of the ovarian and menstrual cycles, and how both end at menopause. Practice Question Which of the following statements about hormone regulation of the female reproductive cycle is false?
LH and FSH are produced in the pituitary, and estradiol and progesterone are produced in the ovaries. Estradiol and progesterone secreted from the corpus luteum cause the endometrium to thicken. The perimetrium is the peritoneal covering of the uterus. It is the birth and copulatory canal. Its anterior wall measures 7. The hymen in virgins closes its lower vestibular end. It has different morphological types: annular, septate, cribriform, fleshy elastic and imperforate. They are the periodic rhythmic changes that occur once about every lunar month 28 days in the female reproductive organs ovary and uterus during the reproductive fertile period from puberty years until menopause years.
They include the ovarian cycle and the uterine endometrial, menstrual cycle. It occurs in the cortex of the ovary. It has three phases: the follicular phase in the first half of the cycle , ovulation at about the middle of the cycle and the luteal phase in the second half of the cycle Figure 2. It entails maturation of the ovarian follicle and secretion of estrogen hormone. Under the effect of the follicle stimulating hormone F. The other follicles undergo atresia atretic follicles.
The developing Graafian follicle secretes estrogen in the liquor folliculi. Estrogen is responsible for the proliferative phase of the uterine cycle. It is the process of rupture of the Graafian follicle and release of the mature ovum from the ovary.
It occurs once every lunar month about 28 days during the fertile period of the human female. It does not occur during pregnancy. It sometimes occurs during lactation. The time of ovulation is variable but it is usually on the 14 th day of the ovarian cycle.
The cause of ovulation is attributed to inhibition of F. It entails formation of the corpus luteum and secretion of progesterone hormone.
Following ovulation, the ovarian follicle passes into the following stages:. After ovulation, the wall of the ovarian follicle collapses and becomes folded due to sudden release of the pressure inside it. Bleeding occurs inside the follicle with the formation of a blood clot. Corpus hemorrhagicum lasts for about three days before it changes into corpus luteum.
The ruptured follicle is gradually transformed into the corpus luteum. The granulose cells enlarge, become polyhedral and develop a yellowish carotenoid pigment the lutein. Now, the cells are termed the granulose luteal cells. At the same time, the theca interna cells undergo similar changes and become the caluteal cells.
The capillaries grow among the luteal cells allowing gradual absorption of the blood clot inside the follicle. They are a follicular phase 12 to 14 days , periovulatory phase 3 days and luteal phase 14 to 16 days. The average length of the ovarian cycle is approximately 27 — 29 days in a healthy woman. However, it can range from 23 to 34 days. Menstrual cycle is the cycle that occurs in the uterus. It is also a cycle that takes place monthly with an average duration of 28 days. Uterine wall prepares for the possibility of an egg to be fertilized and settle in the uterus.
Furthermore, it prepares for the supply of nutrients to developing embryo inside the uterus if the woman gets pregnant. If it not occurs, the developed uterine mucous membranes die and come out through the vagina.
It is the phase called menstruation that lasts for 3 to 5 days. The other two phases of the menstrual cycle are a proliferative phase and the secretory phase.
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