Female Reproductive System
Ovaries
The ovaries lie in shallow depressions, one on each side of the upper pelvic cavity. A longitudinal section through an ovary shows that it is made up of an outer cortex and an inner medulla. There are many sadike structures, called follicles, in the cortex, each of which contains an immature egg called an oocyte. A female is born with as many as 2 million follicles, but the number is reduced to 300,000 to 400,000 by puberty. Only a small number of follicles (about 400) reach maturation because a female usually produces only one egg per month during her reproductive years.
As the follicle undergoes maturation, it develops from a primary follicle into a secondary follicle and, finally, into a vesicular (Graafian) (graf'e-an) follicle.
Oogenesis (oUo-jen' e-sis) (production of eggs) takes place in the follicles. In a primary follicle, a primary oocyte (egg) has 46 chromosomes and divides meiotically into two cells, each having 23 chromosomes. One of these cells, termed the secondary oocyte (egg), receives almost all the cytoplasm. The other is a polar body that disintegrates. A secondary follicle contains the secondary oocyte, which i pushed to one side of a fluid-filled cavity. In a vesicular follicle, pressure within the fluid-filled cavity increases to the
point that the follicular wall balloons out on the surface of the ovary. The wall then bursts, releasing the egg. The egg is surrounded by follicular cells, which collectively are called the corona radiata. This process is referred to as ovulation.
Once a follicle has lost its egg, it develops into a corpus luteum (kor'pus lu'te-um), a glandlike structure. If pregnancy does not occur, the corpus luteum begins to degenerate after about 10 days. If pregnancy does occur, the corpus lute urn persists for three to six months. The follicle and the corpus luteum secrete the female sex hormones estrogen and progesterone.
Cancer of an ovary, or ovarian cancer causes more deaths than cervical and uterine cancer.
Genital Tract
The female genital tract includes the uterine tubes, uterus, and vagina.
Uterine Tubes
The uterine tubes, also called fallopian tubes or oviducts, extend from the uterus to the ovaries. The uterine tubes are not attached to the ovaries; instead, they have fingerlike projections called fimbriae (fim'bre-a) that sweep over the ovary at the time of ovulation. When the egg bursts from the ovary during ovulation, it is usually swept up into a uterine tube by the combined action of the fimbriae and the beating of cilia that line the uterine tubes.
Once in the uterine tube, the egg is propelled slowly toward the uterus by muscular contractions and the cilia of epithelial cells. Fertilization, the completion of oogenesis, and zygote formation normally occur in a uterine tube. The developing embryo usually arrives at the uterus after several days and then embeds, or implants, itself in the uterine lining, which has been prepared to receive it.
Occasionally, the embryo becomes embedded in the wall of a uterine tube, where it begins to develop. Tubular pregnancies cannot succeed because the tubes are not anatomically capable of allowing full development to occur. Such a pregnancy is called an ectopic (ek-tah'pik) pregnancy because it occurs outside the uterus.
Uterus
The uterus is a thick-walled, muscular organ about the size and shape of an inverted pear. Normally, it lies above and is tipped over the urinary bladder. The uterine tubes join the uterus anteriorly, while posteriorly, the cervix, the narrow end of the uterus, projects into the vagina at nearly a right angle. A small opening in the cervix leads to the lumen of the vagina.
Development of the embryo normally takes place in the uterus. This organ, sometimes called the womb, is approximately 5 centimeters (2 inches) wide in its usual state but is capable of stretching to over 30 centimeters (12 inches) to accommodate the growing baby. The lining of the uterus, called the endometrium, participates in the formation of the placenta, which supplies nutrients needed for embryonic and fetal development. The endometrium has two layers: a basal layer and an inner functional layer. In the nonpregnant female, the functional layer of the endometrium varies in thickness according to a monthly reproductive cycle, called the uterine cycle.
Cancer of the cervix is a common form of cancer in women. Early detection is possible by means of a Pap smear, which entails the removal of a few cells from the region of the cervix for microscopic examination. If the cells are cancerous, a hysterectomy (the removal of the uterus) may be recommended. Removal of the ovaries in addition to the uterus is termed an ovariohysterectomy (o-var"e-ohis-ter-ek'to-me). Because the vagina remains intact, the woman still can engage in sexual intercourse.
Vagina
The vagina is a tube that makes a 45° angle with the small of the back. The mucosal lining of the vagina lies in folds that extend when the fibromuscular wall stretches. This capacity to extend is especially important when the vagina serves as the birth canal, and it can also facilitate intercourse, when the vagina receives the penis.
The egg enters the uterine tubes, which lead to the uterus. where implantation and development occur. The vagina is the organ of sexual intercourse in females.
External Genitals
The female external genitals are known collectively as the vulva. The vulva includes two large, haircovered folds of skin called the labia majora. They extend posteriorly from the mons pubis, a fatty prominence underlying the pubic hair. The labia minora are two small folds of skin lying just inside the labia majora. They extend forward from the vaginal opening to encircle and form a foreskin for the clitoris (kli'to-ris), an organ that is homologous to the penis. Although quite small, the clitoris has a shaft of erectile tissue and is capped by a pea-shaped glans. The clitoris also has sensory receptors that allow it to function as a sexually sensitive organ.
The vestibule, a cleft between the labia minora, contains the orifices of the urethra and the vagina. The vagina can be partially closed by a ring of tissue called the hymen. The hymen ordinarily is ruptured by initial sexual intercourse; however, it can also be disrupted by other types of physical activities. If the hymen persists after sexual intercourse, it can be surgically ruptured.
The urinary and reproductive systems in the female are entirely separate: The urethra carries only urine, and the vagina serves only as the birth canal and as the organ for sexual intercourse.
Orgasm in Females
Sexual response in the female is not as distinct as in the male, but there are certain similarities. The clitoris is an especially sensitive organ for initiating sexual sensations. It can become slightly erect as its erectile tissues become engorged with blood, but vasocongestion is more obvious in the labia minora, which expand and deepen in color. Erectile tissue within the vaginal wall also expands with blood, and the added pressure in these blood vessels causes small droplets of fluid to squeeze through the vessel walls and to lubricate the vagina. During orgasm, females experience release from muscular tension, especially in the region of the vulva and vagina but also throughout the entire body. Increased uterine motility may assist the transport of sperm toward the uterine tubes. Since female orgasm is not signaled by ejaculation, there is a wide range in normalcy of sexual response.
Regulation of Female Hormone levels
Hormone regulation in the female is quite complex, so this discussion has been simplified for easy understanding. The following glands and hormones are involved in hormonal regulation:
Hypothalamus secretes GnRH (gonadotropic-releasing hormone)
Anterior pituitary secretes FSH (follicle-stimulating hormone) and LH (luteinizing hormone), the gonadotropic hormones
Ovaries secrete estrogen and progesterone, the female sex hormones The female sex hormones, estrogen and progesterone, have many effects on the body. In particular, estrogen secreted at the time of puberty stimulates the growth of the uterus and the vagina. Estrogen is necessary for egg maturation and is largely responsible for female secondary sexual characteristics. For example, it is responsible for the onset of the uterine cycle, as well as for female body hair and fat distribution. In general, females have a more rounded appearance than males because of a greater accumulation of fat beneath the skin. Also, the pelvic girdle enlarges in females so that the pelvic cavity has a larger relative size compared to males; this means that females have wider hips. Both estrogen and progesterone are also required for breast development.
