Female Reproductive System
Like the male reproductive system, a primary function of the female reproductive system is to make gametes , the specialized cells that contribute half of the total genetic material of a new person. The female reproductive system has several additional functions: to be the location for joining of the male and female gametes, to protect and nourish the new human during the period of gestation , and to nourish the newborn infant for some time after birth, though lactation and nursing.
The parts of the female reproductive tract normally include two ovaries, two uterine tubes (also called fallopian tubes ), a single pear-shaped uterus, and a single vagina. Gamete production is the responsibility of the ovaries, whereas protection and nourishment of the growing embryo and fetus before birth are functions of the uterus. The two uterine tubes, one from each ovary, provide pathways for the female gametes (eggs) to get from the ovaries to the uterus.
The Menstrual Cycle
The primary follicles located in the ovary contain the only cells in the female that can complete the special form of cell division (meiosis) that produces gametes. In females the mature gametes are called egg cells or ova. The production of mature ova is not continuous. Each twenty-eight days or so, one primary follicle (containing one ovum) matures under the influence of hormones from the anterior pituitary, hypothalamus, and the ovary itself. The process of release of a mature ovum from a mature follicle is called ovulation.
Hormonal Control of Female Reproduction
Hormones typically coordinate functions in several different organs at the same time. Considerable coordination among the organs of the female reproductive tract is required. Reproduction will not be successful unless ovulation at the ovary occurs near the time when the uterus is prepared to receive the pre-embryo and, soon thereafter, begin forming the placenta. Without a functional placenta the pregnancy will not continue very long after implantation of the blastocyst. A suite of hormones begin preparing the uterus to receive a fertilized egg and control the development of the next ovum. The ovaries, the anterior pituitary, and the hypothalamus all have endocrine secretions involved in the control of female reproduction.
Changes Associated with Conception and Pregnancy
In a normal menstrual cycle, only one fertilizable ovum is released. It remains capable of being fertilized for only about twenty-four hours following ovulation, whereas sperm cells may remain capable of fertilizing an ovum for as long as seventy-two hours after they have been deposited into the woman's reproductive tract by sexual intercourse. Once deposited, the male's gametes must swim upward through the fluids within the vagina and uterus to arrive at a freshly ovulated ovum in the uterine tube.
Mammary Glands and Lactation
Newborn infants are not able to feed themselves. The same hormones that are responsible for the changes in the ovaries and uterus during the pregnancy also alter the internal function of the woman's mammary glands. The synthesis of mother's milk begins after the delivery of the newborn. An additional peptide hormone called prolactin is secreted from the anterior pituitary. Prolactin helps maintain the secretory capability of the mammary glands for as long as the baby continues to suckle.