Female Reproductive System

This page outlines the basic anatomy and function of the female reproductive system. Separate pages describe the male reproductive system and characteristics of the reproductive system common to both males and females.

1. Anatomy of the female reproductive system:
   1. The entire external genitalia of the female is called the vulva. This includes the labia majora, labia minora and clitoris.
   2. The vagina connects the vulva to the uterus, serving both as a receptacle for sperm during sexual intercourse and as the passageway for the infant during birth. The urethra ends in a separate orifice. The cervix is the neck of the uterus that protrudes into the upper end of the vagina.
   3. The walls of the uterus contain a thick layer of smooth muscle called the myometrium, which serve to expel the fetus during labor. The inner lining of the uterus, the endometrium, proliferates in preparation for implantation of the zygote and is then shed during each menstrual cycle.
   4. Two Fallopian tubes, one on each side, connect the uterus to the ovaries. Fertilization typically occurs here.
   5. Closely associated with the end of each Fallopian tube is a walnut-sized ovary, the female gonad.
2. Egg production takes place within the ovaries:
   1. In the male, all phases of spermatid production from germ cell to gamete takes place continually over the entire lifespan. In the female, each phase takes place during specific periods. About 7 million germ cells, or oogonia, develop in the embryonic ovary as early as 5 months of gestation. Most of these cells then die, with about a half a million of them proceeding through the first stage of meiosis to become primary oocytes before birth.
   2. After puberty, the primary oocytes then begin to develop a few at a time, with each contained in a follicle of surrounding supporting cells.
   3. One or more ovarian follicles rupture at the midpoint of each menstrual cycle, releasing an egg and surrounding cells into the fallopian tube.
3. Hormone production in the ovaries occurs primarily within the developing follicles. The two major steroid hormones produced by the human ovaries are progresterone and estradiol, a form of estrogen. Production of these two hormones varies widely over the course of the menstrual cycle:
   1. The first day of menstruation is usually labeled as the beginning of the cycle. At this point, rising levels of FSH stimulate the development of several follicles in the ovaries. These early follicles in turn begin to produce estrogen. Usually, only one of these follicles will develop past the early stage.
   2. Estrogen levels continue to rise as the follicle develops. Progesterone eventually begin to rise as well. Up to a certain point, the estrogen being produced exerts negative feedback on both GnRH and gonadotropin secretion.
   3. Around the 14th day of the cycle, the anterior pituitary abruptly changes its response to the persistently high estrogen levels. Rather than suppressing gonadotropin release, the estrogen now has a positive feedback effect. The reasons for this switch are still not clear.
   4. The switch to positive feedback provokes a steep surge in LH, and to a lesser degree FSH. High LH levels in turn initiates the process of ovulation, whereby the follicle ruptures and egg is released.
   5. After ovulation, the follicle collapses and the cells within it transform. This new structure is called the corpus luteum. The luteal cells produce more progesterone than estrogen, so blood levels of progesterone rise higher than estrogen levels after ovulation. The corpus luteum only remains viable for about 14 days, after which both estrogen and progesterone levels taper off. The declining levels of estrogen remove the negative feedback on GnRH and FSH production, allowing the cycle to begin over again.

See also: