Module 3 Lesson 6 - 5

Lesson Summary

Sexual maturation in females occurs with the onset of puberty. Puberty begins when GnRH is released from the hypothalamus and acts on the anterior pituitary to produce the reproductive pituitary hormones, FSH and LH. FSH and LH then activate the female gonads, the ovaries, to produce the ovarian hormones, progesterone and estrogen, throughout the course of the ovarian and uterine events of the menstrual cycle.

The menstrual cycle is said to begin on the first day of bleeding and is usually a 28-day cycle. On the first day of menstrual flow, the corpus luteum degeneration causes estrogen and progesterone to be at low levels in the blood. Estrogen blood levels begin to rise as a new follicle begins to mature, releasing the ovarian hormone. When estrogen levels are high, it causes the endometrium to thicken. A more rapid thickening of the endometrium lining occurs after the corpus luteum begins to produce progesterone, which occurs after ovulation. If fertilization occurs, the zygote travels through the Fallopian tube and implants in the freshly, blood-engorged endometrial lining of the uterus. If fertilization does not occur, the endometrium lining disintegrates is expelled from the body during menstruation. Without this intricate dance of pituitary and ovarian hormones, the menstrual cycle would not occur, and fertilization would be impossible.

Hormones are used to prevent and/or assist pregnancies. Reproductive hormones are used in the treatment of conditions such as cancer and arthritis. Many chemicals that are used in products that promote improvement in our daily lives are now being identified as affecting our endocrine system. Evidence now supports that the use of reproductive hormones, although beneficial to us at times, can have adverse effects on human health and may affect many other organisms as well.