1.1 INTERNAL FEMALE ORGANS
The internal organs of the female consists of the uterus, vagina, fallopian tubes, and the ovaries (see Figures 1-1 and 1-2).
Figure 1-2. Anterior view of the uterus and related structures.
a. Uterus. The uterus is a hollow organ about the size and shape of a pear. It serves two important functions: it is the organ of menstruation and during pregnancy it receives the fertilized ovum, retains and nourishes it until it expels the fetus during labor.
(1) Location. The uterus is located between the urinary bladder and the rectum. It is suspended in the pelvis by broad ligaments.
(2) Divisions of the uterus. The uterus consists of the body or corpus, fundus, cervix, and the isthmus. The major portion of the uterus is called the body or corpus. The fundus is the superior, rounded region above the entrance of the fallopian tubes. The cervix is the narrow, inferior outlet that protrudes into the vagina. The isthmus is the slightly constricted portion that joins the corpus to the cervix.
(3) Walls of the uterus (see Figure 1-3). The walls are thick and are composed of three layers: the endometrium, the myometrium, and the perimetrium. The endometrium is the inner layer or mucosa. A fertilized egg burrows into the endometrium (implantation) and resides there for the rest of its development. When the female is not pregnant, the endometrial lining sloughs off about every 28 days in response to changes in levels of hormones in the blood. This process is called menses. The myometrium is the smooth muscle component of the wall. These smooth muscle fibers are arranged. In longitudinal, circular, and spiral patterns, and are interlaced with connective tissues. During the monthly female cycles and during pregnancy, these layers undergo extensive changes. The perimetrium is a strong, serous membrane that coats the entire uterine corpus except the lower one fourth and anterior surface where the bladder is attached.
Figure 1-3. Walls of the uterus.
(1) Location. The vagina is the thin in walled muscular tube about 6 inches long leading from the uterus to the external genitalia. It is located between the bladder and the rectum.
(2) Function. The vagina provides the passageway for childbirth and menstrual flow; it receives the penis and semen during sexual intercourse.
c. Fallopian Tubes (Two).
(1) Location. Each tube is about 4 inches long and extends medially from each ovary to empty into the superior region of the uterus.
(2) Function. The fallopian tubes transport ovum from the ovaries to the uterus. There is no contact of fallopian tubes with the ovaries.
(3) Description. The distal end of each fallopian tube is expanded and has finger-like projections called fimbriae, which partially surround each ovary. When an oocyte is expelled from the ovary, fimbriae create fluid currents that act to carry the oocyte into the fallopian tube. Oocyte is carried toward the uterus by combination of tube peristalsis and cilia, which propel the oocyte forward. The most desirable place for fertilization is the fallopian tube.
d. Ovaries (2) (see figure 1-4).
Figure 1-4. Human ovary.
(1) Functions. The ovaries are for oogenesis-the production of eggs (female sex cells) and for hormone production (estrogen and progesterone).
(2) Location and gross anatomy. The ovaries are about the size and shape of almonds. They lie against the lateral walls of the pelvis, one on each side. They are enclosed and held in place by the broad ligament. There are compact like tissues on the ovaries, which are called ovarian follicles. The follicles are tiny sac-like structures that consist of an immature egg surrounded by one or more layers of follicle cells. As the developing egg begins to ripen or mature, follicle enlarges and develops a fluid filled central region. When the egg is matured, it is called a graafian follicle, and is ready to be ejected from the ovary.
(3) Process of egg production--oogenesis (see Figure 1-5).
(a) The total supply of eggs that a female can release has been determined by the time she is born. The eggs are referred to as "oogonia" in the developing fetus. At the time the female is born, oogonia have divided into primary oocytes, which contain 46 chromosomes and are surrounded by a layer of follicle cells.
(b) Primary oocytes remain in the state of suspended animation through childhood until the female reaches puberty (ages 10 to 14 years). At puberty, the anterior pituitary gland secretes follicle-stimulating hormone (FSH), which stimulates a small number of primary follicles to mature each month.
Figure 1-5. The process of oogenesis.
(c) As a primary oocyte begins dividing, two different cells are produced, each containing 23 unpaired chromosomes. One of the cells is called a secondary oocyte and the other is called the first polar body. The secondary oocyte is the larger cell and is capable of being fertilized. The first polar body is very small, is nonfunctional, and incapable of being fertilized.
(d) By the time follicles have matured to the graafian follicle stage, they contain secondary oocytes and can be seen bulging from the surface of the ovary. Follicle development to this stage takes about 14 days. Ovulation (ejection of the mature egg from the ovary) occurs at this 14-day point in response to the luteinizing hormone (LH), which is released by the anterior pituitary gland.
(e) The follicle at the proper stage of maturity when the LH is secreted will rupture and release its oocyte into the peritoneal cavity. The motion of the fimbriae draws the oocyte into the fallopian tube. The luteinizing hormone also causes the ruptured follicle to change into a granular structure called corpus luteum, which secretes estrogen and progesterone.
(f) If the secondary oocyte is penetrated by a sperm, a secondary division occurs that produces another polar body and an ovum, which combines its 23 chromosomes with those of the sperm to form the fertilized egg, which contains 46 chromosomes.
(4) Process of hormone production by the ovaries.
(a) Estrogen is produced by the follicle cells, which are responsible for secondary sex characteristics and for the maintenance of these traits. These secondary sex characteristics include the enlargement of fallopian tubes, uterus, vagina, and external genitals; breast development; increased deposits of fat in hips and breasts; widening of the pelvis; and onset of menses or menstrual cycle.
(b) Progesterone is produced by the corpus luteum in presence of LH in the blood. It works with estrogen to produce a normal menstrual cycle. Progesterone is important during pregnancy and in preparing the breasts for milk production.
External Female Genitalia
The external organs of the female reproductive system include the mons pubis, labia majora, labia minora, vestibule, perineum, and the Bartholin's glands. As a group, these structures that surround the openings of the urethra and vagina compose the vulva, from the Latin word meaning covering. See Figure 1-6.
Figure 1-6. External female genitalia.
a. Mons Pubis. This is the fatty rounded area overlying the symphysis pubis and covered with thick coarse hair.
b. Labia Majora. The labia majora run posteriorly from the mons pubis. They are the 2 elongated hair covered skin folds. They enclose and protect other external reproductive organs.
c. Labia Minora. The labia minora are 2 smaller folds enclosed by the labia majora. They protect the opening of the vagina and urethra.
d. Vestibule. The vestibule consists of the clitoris, urethral meatus, and the vaginal introitus.
(1) The clitoris is a short erectile organ at the top of the vaginal vestibule whose function is sexual excitation.
(2) The urethral meatus is the mouth or opening of the urethra. The urethra is a small tubular structure that drains urine from the bladder.
(3) The vaginal introitus is the vaginal entrance.
e. Perineum. This is the skin covered muscular area between the vaginal opening (introitus) and the anus. It aids in constricting the urinary, vaginal, and anal opening. It also helps support the pelvic contents.
f. Bartholin's Glands (Vulvovaginal or Vestibular Glands). The Bartholin's glands lie on either side of the vaginal opening. They produce a mucoid substance, which provides lubrication for intercourse.
The blood supply is derived from the uterine and ovarian arteries that extend from the internal iliac arteries and the aorta. The increased demands of pregnancy necessitate a rich supply of blood to the uterus. New, larger blood vessels develop to accommodate the need of the growing uterus. The venous circulation is accomplished via the internal iliac and common iliac vein.
Facts About the Menstrual Cycle
Menstruation is the periodic discharge of blood, mucus, and epithelial cells from the uterus. It usually occurs at monthly intervals throughout the reproductive period, except during pregnancy and lactation, when it is usually suppressed.
a. The menstrual cycle is controlled by the cyclic activity of follicle stimulating hormone (FSH) and LH from the anterior pituitary and progesterone and estrogen from the ovaries. In other words, FSH acts upon the ovary to stimulate the maturation of a follicle, and during this development, the follicular cells secrete increasing amounts of estrogen (see Figure 1-7).
Figure 1-7. Menstrual cycle.
b. Hormonal interaction of the female cycle are as follows:
(1) Days 1-5. This is known as the menses phase. A lack of signal from a fertilized egg influences the drop in estrogen and progesterone production. A drop in progesterone results in the sloughing off of the thick endometrial lining which is the menstrual flow. This occurs for 3 to 5 days.
(2) Days 6-14. This is known as the proliferative phase. A drop in progesterone and estrogen stimulates the release of FSH from the anterior pituitary. FSH stimulates the maturation of an ovum with graafian follicle. Near the end of this phase, the release of LH increases causing a sudden burst like release of the ovum, which is known as ovulation.
(3) Days 15-28. This is known as the secretory phase. High levels of LH cause the empty graafian follicle to develop into the corpus luteum. The corpus luteum releases progesterone, which increases the endometrial blood supply. Endometrial glands secrete nutrients into the uterine cavity, helping to prepare the lining for the arrival of the fertilized egg. If the egg is fertilized, the embryo produces human chorionic gonadotropin (HCG). Thehuman chorionic gonadotropin signals the corpus luteum to continue to supply progesterone to maintain the uterine lining. Continuous levels of progesterone prevent the release of FSH and ovulation ceases.
c. Additional Information.
- (1) The length of the menstrual cycle is highly variable. It may be as short as 21 days or as long as 39 days.
- (2) Only one interval is fairly constant in all females, the time from ovulation to the beginning of menses, which is almost always 14-15 days.
- (3) The menstrual cycle usually ends when or before a woman reaches her fifties. This is known as menopause.
Ovulation is the release of an egg cell from a mature ovarian follicle (see figure 1-5 for ovulation). Ovulation is stimulated by hormones from the anterior pituitary gland, which apparently causes the mature follicle to swell rapidly and eventually rupture. When this happens, the follicular fluid, accompanied by the egg cell, oozes outward from the surface of the ovary and enters the peritoneal cavity. After it is expelled from the ovary, the egg cell and one or two layers of follicular cells surrounding it are usually propelled to the opening of a nearby uterine tube. If the cell is not fertilized by union of a sperm cell within a relatively short time, it will degenerate.
Menopause is the cessation of menstruation. This usually occurs in women between the ages of 45 and 50. Some women may reach menopause before the age of 45 and some after the age of 50. In common use, menopause generally means cessation of regular menstruation. Ovulation may occur sporadically or may cease abruptly. Periods may end suddenly, may become scanty or irregular, or may be intermittently heavy before ceasing altogether. Markedly diminished ovarian activity, that is, significantly decreased estrogen production and cessation of ovulation, causes menopause.