Female Reproductive Hormone Cycles

The Human Female Reproductive System The ovaries are where meiosis occurs and where the secondary oocyte forms prior to birth. The oviducts or Fallopian tubes are where fertilization occurs. After ovulation, the egg moves through the oviduct to the uterus The uterus is where the blastocyst will implant and where the embryo will develop during the nine month gestation if fertilization has occurred. The endometrium is the outter lining of the uterus that will thicken monthly in preparation for the implantation of the blastocyst. The vagina is the birth canal. The cervix is the mouth of the uterus through which the baby will pass though before entering the vagina

The Menstrual Cycle Follicular Phase- Several follicles in the ovaries will grow and secrete large amounts of estrogen in response to follicle stimulating hormone(FSH) from the anterior pituitary. Ovulation- The secondary oocyte ruptures out of the ovaries in response to the luteinizing hormone. Luteal Phase- The corpus luteum forms in response to luteinizing hormone. This is the follicle left behind after ovulation and that of which secretes estrogen and progesterone which thickens the endometrium of the uterus. Menstruation – The monthly shedding of the lining of the uterus when implantation of an embryo does not occur.

Follicular Phase Follicular Phase: This phase begins on the first day of menstrual bleeding. The main event is the development of follicles in the ovaries. At the beginning of the follicular phase, the lining of the uterus (endometrium) is thickened with fluids and nutrients that are used to nourish an embryo. If no egg has been fertilized, estrogen and progesterone levels are low. As a result, the top layers of the endometrium are shed, and menstrual bleeding occurs. About this time, the pituitary gland slightly increases its production of follicle-stimulating hormone. This hormone then stimulates the growth of 3 to 30 follicles. Each follicle contains an egg. Later in the phase, as the level of this hormone decreases, only one of these follicles (called the dominant follicle) continues to grow. It soon begins to produce estrogen, and the other stimulated follicles begin to break down. On average, the follicular phase lasts about 13 or 14 days. This phase ends when the level of luteinizing hormone increases dramatically (surges). The surge results in release of the egg (ovulation).

Ovulatory Phase Ovulatory Phase: This phase begins when the level of luteinizing hormone surges. Luteinizing hormone stimulates the dominant follicle to rupture which releases the egg. The ovulatory phase usually lasts 16 to 32 hours. It ends when the egg is released. About 12 to 24 hours after the egg is released, the surge in luteinizing hormone can be detected by measuring the level of this hormone in urine. The egg can be fertilized for only up to about 12 hours after its release. Fertilization is more likely when sperm are present in the reproductive tract before the egg is released.

Luteal Phase Luteal Phase: This 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 quantities of progesterone. The progesterone produced causes the endometrium to thicken, filling nutrients to nourish a fetus. Progesterone causes the mucus in the cervix to thicken, so that sperm or bacteria are less likely to enter the uterus. During the luteal phase, the estrogen levels are high. Estrogen stimulates the endometrium to thicken. The increase in estrogen and progesterone levels causes milk ducts in the breasts to widen (dilate). If the egg is not fertilized, the corpus luteum degenerates after 14 days, and a new menstrual cycle begins. If the egg is fertilized, the cells around the developing embryo produce a hormone called human chorionic gonadotropin. This hormone maintains the corpus luteum, which prodces progesterone.

Types of Hormones Estrogen Estrogens are a group of hormones that are essential for the sexual and reproductive development of women. Estrogen hormones are produced in the ovaries, the adrenal glands play a small role in producing estrogen hormones. Estrogen plays an important role in the regulation of the menstrual cycle Progesterone Progesterone is also a female sex hormone and is vital for the regulation of various bodily functions. Progesterone is produced in the ovaries. Progesterone controls a woman’s monthly menstrual cycle and prepares the body for pregnancy. Testosterone Testosterone is one of the six hormones produced by the female reproductive organs. Testosterone has an important function in men and women and the health and sexual functioning of the body. The effects of testosterone are more visible in men but they are still vitally important for women. DHEA Dehydroepiandrosterone (DHEA) is a natural steroid hormone that is derived from cholesterol and is produced in the adrenal glands. DHEA is similar in chemical composition to testosterone and estrogen and is easily converted into these hormones by the body. After production, the bloodstream carries DHEA to tissues and cells.

Positive and Negative Feedback of Menstrual Cycle Positive feedback in the menstrual cycle: Positive feedback enhances a process until it is complete. During the follicular phase, estrogen released from the follicle stimulates the release of the Luteinizing hormone from the anterior pituitary. This increase stimulates the follicle to release an excess amount of estrogen. The hormone levels continuously rise until the follicle matures and ovulation occurs. Negative feedback in the menstrual cycle: Negative feedback stops a process once homeostasis is reached. Luteinizing hormone stimulates the corpus luteum to secrete estrogen and progesterone. Once the levels of estrogen and progesterone reach high levels, they trigger the hypothalamus and pituitary to shut off which inhibits the secretion of the luteinizing hormone and follicular stimulating hormone.