THE FEMALE REPRODUCTIVE ORGANS AND THEIR FUNCTIONS

THE UTERUS

The uterus, or womb, is a hollow organ situated within the pelvic cavity. It is rather like an inverted pear with the sharp end (cervix) pushing down into the upper end of the vagina. The uterus consists of two parts: the body and the cervix.

The body of the uterus, containing the uterine cavity, constitutes approximately two-thirds of the uterus, and the cervix comprises the other third. The upper part of the uterus is known as the fundus. The cavity of the uterus is triangular in shape with the Fallopian tubes entering at the upper and outer corners of the triangle.

The cervix, or neck of the uterus, protrudes into the vagina where it can be felt as a firm, hard, fibrous dome-shaped structure which varies in diameter from 1 to 3.5cm. Through its centre the cervical canal extends upwards for about 1 to 3.5 cm. until it enters the cavity of the uterus.

The uterus is composed almost entirely of special muscle, together with a small quantity of fibrous tissue. There is no voluntary control over the muscle of the uterus. It is known as involuntary or smooth muscle, and is similar in this respect to the muscle of the intestine, of the blood vessels and to the highly specialized muscle of the heart. 

You can move your arms and legs by exerting control over the muscles in your limbs, but you have no conscious influence over the involuntary muscle of your heart, intestine, blood vessels, or of your uterus. The walls of the body of the uterus are approximately 1 cm thick and the muscle fibers themselves are arranged in three different directions. Some encircle the uterus, some extend up, over the top and down the other side, while others are oblique and spiral. Because the cervix contains more fibrous tissue than the uterine body, it is much firmer and harder than the body of the uterus.

FIG 1.1 THE UTERUS 

The cavity of the uterus is lined by a mucous membrane called the endometrium. This is a highly specialized layer of glandular tissue which is shed at menstruation and which is converted under the influence of hormones to form the deciduas that is essential to the preservation and continuation of pregnancy.

It must be clearly understood that all the pelvic organs are freely movable. The uterus and cervix can be moved painlessly not only up and down but also sideways and from front to back. The uterus normally lies titled forwards in a position that is known as anteversion with its fundus, or upper part, against the bladder. When the bladder fills, the uterus is pushed upwards and backwards so that it comes to lie in direct line with the vagina.

If the uterus is tilted backwards, it is known as retroversion, sometimes called tilted uterus or upside-down uterus. A great deal of mystery surrounds the retroverted uterus. Approximately 20 percent, or one in five, of all women have a uterus that is tilted backwards. 

This is known as a congenital retroversion and is absolutely normal. It has been in this position from birth and it will remain in this position (unless operated upon, or during pregnancy) for the duration of life. It does not cause any difficulties during menstruation or problems of infertility; nor does it predispose to miscarriage or lead to complications in labour.

The problem occurs if the uterus becomes retroverted as a result of disease or infection. This is known as acquired retroversion and may give rise to symptoms that are caused by the predisposing disease or infection.

The uterus is supported firstly by the pelvic floor and, secondly, by the tri-radiate ligament attached to the upper part of the cervix. This ligament consists of three parts. One runs forwards to the back of the symphysis, the second runs laterally to the side wall of the pelvis and the third goes backwards to be attached to the front part of the sacrum. All the outer ends of the tri-radiate ligament are attached to the bony pelvis and they form a type of hammock, suspending the uterus in the centre of the pelvis above the pelvic floor and allowing it considerable freedom of movement.

The blood supply to the uterus comes from the main blood vessels in the pelvis. This blood supply is very good and ample, and has an ability to increase to many times its volume during pregnancy.

The nerve supply to the uterus is very complicated. The muscle contracts rhythmically, especially during labour and during menstruation. 

Sensations coming from the uterus and similar to those that emanate from the intestine; in other words, the uterus only responds to stretching and this alone will cause discomfort. It can be cut or the cervix burnt as in cauterization of an ulcer on the cervix without any pain or discomfort. Stretching, however, of either the cervix or the uterus may cause quite severe pain.

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THE FALLOPIAN TUBES

The Fallopian or uterine tubes are a pair of ducts which are attached to the upper and outer corners of the uterus. Each is approximately 10cm long and about half a centimeter thick, although the size varies in its different parts. The ampulla or outer end of the Fallopian tube forms a funnel-like opening where the wall divides into finger-like processes called fimbriate. These not only guard the opening but, close to the ovary, they also help to sweep the ovum into the canal of the tube itself. Fertilization occurs in the outer part of the Fallopian tube in the region of the ampulla.

The Fallopian tubes consist of a fairly thick muscular coat surrounding a very complex inner lining, or mucous membrane, which secretes special material to nourish both the sperms and the fertilized ovum.

The function of the Fallopian tube is essentially twofold in nature. Firstly, it forms a route whereby the sperms migrate from the uterus to the ovary, and it possesses certainly vital characteristics which enable it to nurture and look after sperms. It is commonly believed that sperms remain alive and capable of fertilization for two or even three days in the outer fimbriated part of the Fallopian tube and they are thus readily available when ovulation occurs. Secondly, the Fallopian tube is the home of the newly fertilized ovum for the first 7 days of its life.

FIG 1.2  FALLOPIAN TUBES

 If the ovum is not fertilized, it can only survive for 12 or perhaps 18 hours. Fertilization occurs on the 14^th day of a 28-day menstrual cycle at the time of ovulation. Immediately after fertilization the ovum enters the fimbriated end of the Fallopian tube (or fertilization actually occurs within the Fallopian tube) and it does not reach the cavity of the uterus until the 21^st day. The Fallopian tube supplies the newly fertilized ovum with all its nutrition and requirements during these 7 days. 

On the 7^th day after fertilization the ovum will have developed chorionic villi which are special protrusions on the outer side of the fertilized egg which enable the pregnancy to embed within whatever maternal tissue is nearest or most convenient at the time.

 It is therefore vital that the journey of the fertilized ovum along the Fallopian tube should take precisely 7 day, no more and no less. If the ovum arrives in the cavity of the uterus before the 7^th day, it is unable to embed itself and therefore dies, or conversely if it fails to arrive in the cavity of the uterus by the 7^th day, it embeds itself within the Fallopian tube and forms an ectopic or tubal pregnancy.

THE OVARY

The ovaries resemble large almonds in shape and size, and are situated one each side of the uterus just below the fimbriated end of the Fallopian tube. They are therefore quite close to the side wall of the pelvis and are protected from damage by the bones which form the pelvic girdle. They are extremely tender if pressure is exerted upon them. 

FIG 1.3 THE OVARY 

In a young girl the surface is smooth and pink, but later it becomes grey and rather puckered due to the formation of repeated tiny scars which are caused by the process of ovulation. After the menopause when there are no more ova remaining, the ovary becomes small, rather shriveled and wrinkled. The ovaries have two main functions: the production of hormones and the production of ova.

PRODUCTION OF HORMONES

The formation or the production of hormones from the ovary is vital to the female throughout her reproductive life. The ovary produces two main hormones: oestrogen and progesterone.

The production of oestrogen commences relatively early in life and is responsible for the development and the maintenance of all the secondary sex characteristics, such as the breasts and body contour as well as the maturation of the vulva and the growth of the vagina, uterus and Fallopian tubes. Oestrogen is also partly responsible for the regulation of the menstrual cycle. At the time of the menopause when the ovaries cease to produce the required amount of oestrogen, the periods stop and symptoms of the menopause develop.

Progesterone is produced from the corpus luteum, which is the small gland that forms in the ovary after ovulation has occurred. This hormone is essential for the maintenance of pregnancy and also for the development of many symptoms during early pregnancy. It is also responsible for ripening the endometrium, or lining of the uterus, during the second half of the menstrual period as well as a normal menstrual flow.

The functioning of the ovary is under the direct control and command of the pituitary gland. This is a small gland situated in the base of the brain and is responsible for controlling most of the glandular secretions throughout the entire body. It not only controls the normal menstrual cycle but is also responsible for the onset, rhythm and eventual cessation of menstruation. The pituitary produces a small amount of an extremely powerful hormone called follicle- stimulating hormone (FSH) which is released into the bloodstream and circulates to the ovary, within which it provokes the formation of follicles.

FIG 1.4 PRODUCTION OF HORMONES

 The developing follicles manufacture oestrogen. One of these follicles ripens and bursts liberating an ovum ovulation. This process is induced by FSH. Another pituitary hormone, called luteinizing hormones (LH), also reaches the ovary via the bloodstream to cause ovulation and form the corpus luteum which can then secrete progesterone. This production of LH prior to ovulation is detected in the modern ovulation prediction urine test available for fertility investigations.

When fertilization occurs, the body has to take firm action to prevent another ovum embeds within the endometrium 7 days after ovulation. This is accomplished by the chorionic villi that surround the fertilized ovum and have the ability to erode maternal tissue.

 The chorionic villi produce a hormone known as chorionic gonadotrophin, which reaches the ovary by way of the maternal bloodstream forcing it to produce more progesterone which, in turn, will suppress the pituitary gland secretion of follicle-stimulating hormone. The net result is that the corpus luteum continues to increase in size, thus increasing the amount of progesterone secreted, while the suppression of the production of follicle- stimulating hormone means that no more follicles ripen in the ovaries.

If fertilization does not occur, the corpus luteum begins to shrivel on about the 26^th day of the cycle. The consequent fall in progesterone as well as in oestrogen level results in menstruation. If, however, fertilization has occurred, then the production of chorionic gonadotrophin from the chorionic villi results in a dramatic increase in secretion of progesterone from the ovarian copus luteum which rapidly enlarges. 

VIDEO 1.1 FEMALE REPRODUCTIVE ORGANS 

The enormous increase in progesterone production together with its prolonged secretion beyond the 26^th day of the menstrual cycle means that menstruation does not occur. The endometrium within the uterus remains intact and the newly implanted pregnancy is allowed to continue growing. Progesterone not only creates the secretory changes in the lining of the uterus, which are essential for the nutrition of the new pregnancy, but it also causes softening and relaxation of the uterine muscle as well as other involuntary muscle throughout the body, especially in the intestine, the bladder and blood vessels.

 It does not affect the heart itself. Relaxation of the muscle in the walls of the many blood vessels occasionally results in a fall in blood pressure , especially when a pregnant woman is standing, and this predisposes her to fainting attacks. Relaxation of the muscular wall of  the intestine predisposes to constipation, which, together with relaxation of the muscular wall of the bladder predispose the pregnant woman to infections in the urinary tract. Progesterone is also responsible for the increase in the size of the breasts during early pregnancy, as well as the nausea which affects most women.

The ovary of the new born female infant contains all the ova which she is likely to need during her life ( together with many more besides). These are formed while the female baby is still in the uterus, and can be damaged during their development. While X-Rays will not damage the baby itself, it is known that they can affect or damage the genetic pattern of the chromosomes within the developing ova of the baby. Pregnant women are therefore X-Rayed as little as possible. Intensive X-Ray investigations are not advisable because of the possibility that the child may be adversely affected or rendered sterile by the effect of X-Rays on the gonads.