Human Reproductive Organs

Human Reproductive Organs

The most prominent physical difference between a man and woman are the sexual organs. In the early stages of the embryo both sexes appear almost identical. It is not until about six weeks after conception that there is any visible difference between a boy and a girl. It is the presence of a Y-chromosome that produces development of a male. In the absence of a Y-chromosome, a female develops. In a man the gametes, or germ cells, are produced in testicles. These are maintained at a temperature slightly below that of the rest of the body, which ensures a continuous supply of sperm. In a woman, however, the production of germ cells is a cyclic occurrence. Every month one germ cell is released and the mucous lining of the womb is prepared to accommodate an impregnated germ cell. If impregnation does not take place this mucous lining and the blood it contains is rejected (menstruation) and its development starts all over again.

In principle the menstrual cycle is only interrupted when a pregnancy occurs. Whereas a grown man is theoretically able to become a father during his entire life, in a woman the fertile phase of her life is clearly limited. From puberty onwards about 400 germ cells are released over approximately 35 years, but after this period it is not possible for any germ cells to mature in the ovaries. Sexual activity, however, becomes no less possible or rewarding.

Female reproductive organs

The biological function of the adult female reproductive organs is to produce ripe egg cells, arrange suitable conditions for their fertilization by a sperm from the male, and then provide a nuturing and protective environment for development of the foetus. The activity of the system is cyclical in the non-pregnant woman, as opposed to the continuous activity of the male’s reproductive system in producing sperm.

An egg is ripened and released every month by the ovary. If the egg is fertilized, the system usually switches smoothly from the regular menstrual cycle to the temporary nine-month ‘diversion’ of pregnancy. The organs of the system can be described in two groups. First are the external organs (genitalia) comprising the vulval or vaginal lips and the clitoris at the entrance of the v,agina. Second are the internal organs which include the vagina, uterus, Fallopian tubes and ovaries. The entire system is in fact a continuous tract or passageway from the outside through the vagina to the uterus, then along the Fallopian tubes to the abdominal cavity where the ovaries are situated. This is the direction in which sperms travel; eggs, and babies, travel in the opposite direction.

The reproductive organs constitute the primary female sexual characteristics; there are other, secondary, sexual characteristics such as the breasts and body-fat distribution.

External organs

The collective name for the external genitalia is the vulva. This is made up of several parts surrounding the entrance to the vagina.

The labia majora (the vaginal lips) are the two large folds of skin forming the outer protective wall of the vulva. They contain sweat glands and hair follicles embedded in fat. The size of the labia majora varies considerably with age. They are small in infancy and old age but during a woman’s fertile years they are filled with fatty tissue and are therefore much larger. They join together in the pad of fat on top of the pelvic bone, the mons pubis. At puberty the mons pubis and the outer surfaces of the labia majora become covered with hair.

The inner surfaces of the labia majora are separated by a thin groove from the labia minora (the small lips) which protect the entrance to the vagina. During the reproductive years they are hidden by the enlarged labia majora, but in childhood and old age they are more prominent as the labia majora are relatively small. They contain many sebaceous glands* but no hairs. They split in front, into two folds, one of which stretches over the clitoris to form the prepuce, the female equivalent of the foreskin, and the other which joins behind it to form a small membranous fold called the frenulum. The area between the folds of the labia minora is known as the vestibule.

The clitoris is descended from the same embryonic structure that becomes the penis in the male and contains erectile tissue which fills with blood during sexual excitement. It varies considerably in size but is normally about 4-6mm in diameter. The movement of a man’s penis into the vagina can stimulate the clitoris during sexual intercourse and can lead to orgasm, in the same way as clitoral stimulation by hand or other physical methods. However, sexual intercourse does not always result in orgasm for a woman, nor is a female orgasm necessary for conception.

Just underneath the clitoris is the external opening of the urinary tract, the urethra, which leads to the bladder. Beneath the urethral orifice is the hymen, a thin layer of mucous membrane which covers part of the opening to the vagina. It varies in shape and elasticity and is usually (but by no means always) stretched or torn during the first attempt at sexual intercourse; this often results in a degree of bleeding. An intact hymen is usually regarded as a sign of virginity but this is not always the case because sometimes sexual intercourse fails to tear the hymen, whereas sexual foreplay without intercourse can cause its breakage. It can also be torn by the use of intravaginal tampons, or it may rupture spontaneously and painlessly during strenuous exercise. Childbirth causes the greatest tearing of the hymen after which only small pieces remain. The vestibule of the vagina is the cleft between the labia minora into which the urethra and the vagina open.

At the posterior end of the vestibule are two vestibular glands, both about the size of a small pea with small ducts leading into the vestibule. The glands, known as Bartholin’s glands, secrete fluid during sexual arousal, moistening the entrance to the vagina and thereby facilitating the entrance of the penis during sexual intercourse. If one of the ducts should become blocked, the gland will become inflamed. This may cause pain and swelling of the labia majoris. Once the inflammation has been suppressed, a cyst* may result which has to be removed surgically if it becomes troublesome.

Between the vulva and the anus is an area, called the perineum, which provides attachment to the muscles of the pelvic floor.

Vagina

The internal reproductive organs which are located in the pelvic cavity – the uterus, the Fallopian tubes and the ovaries – communicate with the outside world by way of the vagina.

The vagina is a fibromuscular tube measuring about 9cm long in an adult woman. It runs obliquely upwards and backwards at an angle of approximately 450 from the vestibule to the uterus, between the bladder

located directly in front and the rectum behind. It is supplied with a well-developed system of veins which distend during sexual arousal. The vaginal walls are normally close together but are capable of expanding to accommodate intravaginal tampons used during menstruation or the penis during sexual intercourse. The greatest expansion of the vagina is seen during childbirth when considerable stretching of both the cervix (neck of the uterus) and the vagina, forming part of the birth canal*, is necessary in order to let the baby pass through.

The vagina has a special mechanism for keeping itself clean. The top cell layer of the 30-cell deep walls of the vagina is continually shed during the reproductive years. These cells are acted on by bacteria and produce lactic acid which kills any contaminating germs which get into the vagina. In old age, when the lining of the vaginal walls becomes thin and few cells are shed, germs may proliferate which may result in inflammation.

Cervix and uterus

At the top of the vagina lies the cervix, the lower opening or ‘neck’ of the uterus. It is the narrowest point of the uterus but during childbirth it can dilate to approximately 10cm in diameter. In the centre of the cervix is a small slit or dimple which forms the opening into the cervical canal and hence into the uterus. The cervical canal is lined with delicate red tissue called columnar epithelium; the mouth of the cervix is covered with a stronger pink tissue called squamous epithelium. The cervix is muscular and keeps the entrance to the uterus tightly shut, letting only something as tiny as a sperm in and, during a period, the flow of menstrual blood out. By way of the vagina, uterus, and oviduct there exists a continuous passage from the outside world into the abdomen of a woman. Under normal circumstances the cervix is practically closed and the oviduct has but a minuscule passage. But its existence must be taken into account in connection with the possible spreading of infections along this passage to the abdominal cavity.

The cervical canal is about 2.5cm long. Its opening into the vagina is called the external os of the uterus. Before childbirth the external os is small, almost circular and often depressed. After childbirth, the front and back of the external os becomes bounded by lips making it appear more slit-like. The tissue lining the cervical canal contains glands that secrete a clear, alkaline mucous. Numerous small cysts are found in this mucous membrane. It is from this region that cervical smears are taken in order to detect changes that may precurse cancer. The cervix is a region that is relatively prone to the development of cancer. Influencing factors are, among others: infections of the sexual organs; the bearing of many children (with a virgin, cancer of the cervix does not exist); and sexual intercourse begun at an early age with a frequent change of partners. Fortunately the cervix can be easily reached, and once sexual activity begins, a smear test* should be conducted to examine for the presence of cancerous cells. Carried out on a regular basis, this test ensures recognition and treatment of cancer at an early stage.

The cervix is the entrance to the uterus or womb. The womb is a pear-shaped muscular structure, lying behind the bladder, and averages 9cm in length and 7cm across at the widest point. It is supported by ligaments and the muscles of the pelvic floor. During pregnancy the uterus increases in weight from 30 grams to more than a kilogram and the walls relax to accommodate the growing foetus and can easily contain a baby over 50cm in length.

The uterus is an extremely strong organ: during childbirth it can exert a pressure of about I kg per square centimetre, with no extra help from the abdomen, to push the baby out.

Yet only a few weeks after the birth, the uterus has shrunk back to its normal size.

The uterine cavity is lined with soft velvety tissue called the endometrium which contains a mass of blood vessels. Unless an egg is fertilized the endometrium is shed each month during the menstrual cycle and then grows again.

From both sides of the body of the uterus extend the Fallopian tubes. Their finger-like ends hover above the ovaries ready to sweep up the expelled egg, and pass it down through the Fallopian tube to the uterus. It takes about six days for the egg to reach the uterus. During this time fertilization may take place. Fertilized eggs implant themselves in the uterine wall; unfertilized eggs, along with the specially prepared uterine lining are flushed out in the menstrual flow.

Removal of the reproductive organs

The uterus, and sometimes also the ovaries and the Fallopian tubes, may be removed to treat any of a number of gynaecological complaints, largely in post-menopausal women. These include the presence of cancer, or of a benign tumour especially if it is large or rapidly growing, or causing excessive bleeding or discomfort. Hysterectomy, as the procedure is called, may also be performed after Cesarean section if there are complications such as uncontrolled bleeding or gross infection.

There are two basic methods for performing a hysterectomy. The most common method is to remove the uterus through an incision in the lower abdomen. The other, much rarer method, involves making an incision at the top of the vagina through which the uterus is removed. For a pre-menopausal woman, a total hysterectomy means sterilization and the end of menstruation. For these women, hormone replacement therapy may be used to prevent the onset of an early menopause – treating the loss of oestrogen, the hormone produced by the ovaries. The ovaries, however, are not nowadays removed in a pre-menopausal woman unless there is good medical reason to do so, for example, in cases of cancer of the ovary, ectopic pregnancy or ovarian cysts.

The consequences of the operation are beset with myth – that hysterectomy makes intercourse impossible, stops the sex drive, and leads to obesity – none of which is true.