The menstrual cycle is divided into three stages: follicular phase, ovulation, and the luteal phase. During the follicular phase or proliferative phase , follicles in the ovary mature under the control of estradiol.
Follicle-stimulating hormone FSH is secreted by the anterior pituitary gland beginning in the last few days of the previous menstrual cycle. Levels of FSH peak during the first week of the follicular phase. The rise in FSH recruits tertiary-stage ovarian follicles antral follicles for entry into the menstrual cycle.
Follicle-stimulating hormone induces the proliferation of granulosa cells in the developing follicles and the expression of luteinizing hormone LH receptors on these cells.
Under the influence of FSH, granulosa cells begin estrogen secretion. This increased level of estrogen stimulates production of gonadotropin-releasing hormone GnRH , which increases production of LH.
LH induces androgen synthesis by theca cells, stimulates proliferation and differentiation, and increases LH receptor expression on granulosa cells. Throughout the entire follicular phase, rising estrogen levels in the blood stimulate growth of the endometrium and myometrium of the uterus. This also causes endometrial cells to produce receptors for progesterone, which helps prime the endometrium to the late proliferative phase and the luteal phase.
Two or three days before LH levels begin to increase, one or occasionally two of the recruited follicles emerge as dominant. This pain is known as mittelschmerz literally, middle pain. The pain may last for a few minutes to a few hours. The pain is usually felt on the same side as the ovary that released the egg, but the precise cause of the pain is unknown.
The pain may precede or follow the rupture of the follicle and may not occur in all cycles. Egg release does not alternate between the two ovaries and appears to be random.
If one ovary is removed, the remaining ovary releases an egg every month. The luteal phase begins after ovulation. It lasts about 14 days unless fertilization occurs and ends just before a menstrual period. In this phase, the ruptured follicle closes after releasing the egg and forms a structure called a corpus luteum, which produces increasing quantities of progesterone. The progesterone produced by the corpus luteum does the following:.
Causes the endometrium to thicken, filling with fluids and nutrients to nourish a potential embryo. Causes the mucus in the cervix to thicken, so that sperm or bacteria are less likely to enter the uterus. Causes body temperature to increase slightly during the luteal phase and remain elevated until a menstrual period begins this increase in temperature can be used to estimate whether ovulation has occurred Overview of Infertility Infertility is usually defined as the inability of a couple to achieve a pregnancy after repeated intercourse without contraception for 1 year.
Frequent intercourse without birth control usually During most of the luteal phase, the estrogen level is high. Estrogen also stimulates the endometrium to thicken. The increase in estrogen and progesterone levels causes milk ducts in the breasts to widen dilate. As a result, the breasts may swell and become tender.
If the egg is not fertilized or if the fertilized egg does not implant, the corpus luteum degenerates after 14 days, levels of estrogen and progesterone decrease, and a new menstrual cycle begins. If the embryo is implanted, the cells around the developing embryo begin to produce a hormone called human chorionic gonadotropin.
This hormone maintains the corpus luteum, which continues to produce progesterone , until the growing fetus can produce its own hormones.
Pregnancy tests are based on detecting an increase in the human chorionic gonadotropin level. Merck and Co. From developing new therapies that treat and prevent disease to helping people in need, we are committed to improving health and well-being around the world.
The Manual was first published in as a service to the community. Learn more about our commitment to Global Medical Knowledge. This site complies with the HONcode standard for trustworthy health information: verify here. Girls get their first period menarche , on average, between the ages of 11 and 14 years.
By this stage, other sexual characteristics have developed, such as pubic hair and budding breasts. The menstrual cycle is complex and is controlled by many different glands and the hormones that these glands produce.
A brain structure called the hypothalamus causes the nearby pituitary gland to produce certain chemicals, which prompt the ovaries to produce the sex hormones oestrogen and progesterone.
The menstrual cycle is a biofeedback system, which means each structure and gland is affected by the activity of the others. Menstruation is the elimination of the thickened lining of the uterus endometrium from the body through the vagina.
Menstrual fluid contains blood, cells from the lining of the uterus endometrial cells and mucus. The average length of a period is between three days and one week. Sanitary pads or tampons are used to absorb the menstrual flow. Both pads and tampons need to be changed regularly at least every four hours. Using tampons has been associated with an increased risk of a rare illness called toxic shock syndrome TSS. The follicular phase starts on the first day of menstruation and ends with ovulation.
Prompted by the hypothalamus, the pituitary gland releases follicle stimulating hormone FSH. This hormone stimulates the ovary to produce around five to 20 follicles tiny nodules or cysts , which bead on the surface.
Each follicle houses an immature egg. Usually, only one follicle will mature into an egg, while the others die. This can occur around day 10 of a day cycle. The growth of the follicles stimulates the lining of the uterus to thicken in preparation for possible pregnancy. Ovulation is the release of a mature egg from the surface of the ovary.
This usually occurs mid-cycle, around two weeks or so before menstruation starts. Learn about other infertility risk factors here. Your overall health is a reflection of your reproductive health. Give yourself a long and healthy life. Consider these tips to stay healthy. Patient Education. Related Conditions. The Hypothalamus and the Pituitary The hypothalamus is located centrally in the brain and communicates by way of an exchange of blood with the pituitary gland.
The Ovary The main function of the ovaries is the production of eggs and hormones. Continue reading As the follicle grows, blood levels of estrogen rise significantly by cycle day seven. Ovulation When the level of estrogen is sufficiently high, it produces a sudden release of LH, usually around day thirteen of the cycle. The Luteal Phase The luteal phase, or second half of the menstrual cycle, begins with ovulation and lasts approximately 14 days — typically 12 to 15 days.
The Uterus The lining of the uterus, or endometrium, prepares each month for the implantation of an embryo. Recommended reading. Conception: How It Works Learn the steps of conception and how each works including, sperm transport, egg transport, fertilization and embryo development, and implantation.
Infertility Risk Factors Maternal age is probably the most significant factor related to a woman's ability to conceive. Reducing Your Risk of Infertility Your overall health is a reflection of your reproductive health.
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