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1-3. Internal Genitalia

Figure 1-1. Female reproductive system.

a. Uterus or Womb.

(1) Description/information. The uterus is a hollow, muscular, pear-shaped organ. It is located in the pelvic cavity between the urinary bladder and the rectum. During a woman's child-bearing years, the uterus is about 7.5 centimeters long, 5 centimeters wide, and 2.5 centimeters thick. The uterus has three anatomical divisions: the fundus, the body, and the cervix. The fundus is the upper, convex part of the uterus. This part is just above the entrance to the uterine tubes. The body is the central portion of the uterus, and the cervix is the lower, neck-like part of the uterus.

(2) Walls. The walls of the uterus are made up of three layers: the endometrium, the myometrium, and the parietal peritoneum. The endometrium, the inner layer, attaches itself to the myometrium layer and lines the uterus. This layer is sloughed off during menstruation or post- delivery. The middle layer, which is composed of smooth muscle, is the myometrium. This layer is made up of longitudinal, circular, and spiral muscular fiber which interlaces. The myometrium is thickest in the fundus and thinnest in the cervix. During childbirth, this muscle layer is capable of the very powerful contractions necessary for a normal birth. The third layer, the parietal peritoneum, is the outer layer which is a serous membrane. This outer layer of uterine wall is incomplete, covering only part of the uterine body and none of the uterine cervix.

(3) Functions. The uterus has three major functions which occur during these events: pregnancy, labor, and menstruation. During pregnancy, the uterus holds the fertilized ovum. The ovum is deposited in the uterus where it grows and develops through the embryo and fetal stages. During the birth process, the uterus produces powerful contractions to expel the mature infant. And, finally, during a female's menstrual phase, the inside lining of the uterus detaches and sloughs off, the uterus expelling its fluid contents.

b. Uterine Tubes, Fallopian Tubes, or Oviducts.

(1) Description/information. These tubes are known by all three names listed above. The name commonly used is fallopian tubes. These two tubes extend from the ovaries to the uterus. An ovum discharged from an ovary passes through one of these tubes to the uterus. Each tube is about 10 centimeters long (4 inches). The tube is located between the folds of the broad ligaments of the uterus. The tubes are attached to the uterus at one end but not attached to the ovaries at the other end. At the ovary end, the tubes are open, funnel-shaped, and close to the ovary. The funnel- shaped ends of the tubes are called the infundibulum, and the fringe or finger-like processes at the tube ends are called fimbriae.

(2) Functions. The uterine tubes are ducts for the ovaries although the tubes are not attached to the ovaries. Additionally, the tubes are the site of fertilization. Fertilization normally takes place in the outer one-third of the tube.

c. Ovaries.

(1) Description/information. The ovaries are two almond-shaped glands. They are located on either side of the uterus, below and behind the uterine tubes. The ovaries are detached from the uterine tubes and held in position by a series of ligaments. During the second phase (preovulatory phase) of the menstrual cycle, one of the 20 to 25 primary follicles developed during the menstrual phase matures into a Graafian follicle, a follicle ready for ovulation. During the maturation process, this follicle increases its estrogen production. The rupture of the Graafian follicle with the release of the ovum is the beginning of ovulation.

(2) Functions. One function of the ovaries is to produce ova (female reproductive cells capable of developing, after fertilization, into new individuals). Also, the ovaries discharge ova (ovulation) and secrete the female sex hormones progesterone, estrogen, and relaxin. The ovaries in the female correspond to the testes in the male reproductive system.

d. Vagina.

(1) Description/information. The vagina is a muscular, tubular organ lined with mucous membrane. This organ is about 10 centimeters (4 inches) long and extends from the hymen to the cervix. The vagina extends upward and backward between the rectum and the bladder and is attached to the uterus.

(2) Structure. The lining of the vagina is made up of smooth muscle which is longitudinally and circularly arranged in many folds called rugae. The folds of the lining permit the organ to expand when necessary. The hymen is the fold of mucous membrane at the orifice (opening) of the vagina.

(3) Functions. The vagina serves as a passageway for menstrual flow, receives seminal fluid from the male, and serves as the lower part of the birth canal.

David L. Heiserman, Editor

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Revised: June 06, 2015