The Ovary

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. In a young girl the surface is smooth and pink, but later it becomes grey and rather puckered due to die 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 shrivelled 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 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. If the level of oestrogen falls very low postmenopausal symptoms develop.

The OvaryProgesterone 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 cycle, which is one of the major factors responsible for a regular 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 (F.S.H.) which is released into the bloodstream and circulates to the ovary, within which it provokes the formation of follicles. The developing follicles manufacture oestrogen. One of these follicles ripens and bursts liberating an ovum—ovulation. This process is caused- by F.S.H. with another pituitary hormone (L.H.) the latter reaching the ovary by the bloodstream to cause ovulation and form’the corpus luteum which can then secrete progesterone.

When fertilization occurs the body has to take firm action to prevent another ovum being released and the next menstrual period occurring. The fertilized ovum embeds within the endometrium seven 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 secrcted, 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 26th 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 gonado-trophin from the chorionic villi results in an increase in secretion of progesterone from the ovarian corpus luteum which rapidly enlarges with a consequent rise in production of progesterone. The enormous increase in progesterone production together with its prolonged secretion beyond the 26th 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 many of the 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 blood vessels round the anal canal may result in the formation of haemorrhoids or piles. Slackening and relaxation of the muscle wall of the bladder and of the muscle in the wall of the ureters that connect the kidneys to 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, or its developing ova, it is known that they can affect the genetic pattern of the chromosomes. 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 develop leukaemia or that future generations may be adversely affected.

Ovulation

Ovulation is a name given to the actual production of an egg by the ovary. The ovaries of the new-born female contain approximately 80,000 ova, which is many more than she will require during her reproductive life. During each menstrual cycle about 250 ova commence to develop, but usually only one is destined to be properly ripened and shed in the middle of the cycle. A developing ovum lies within a small cyst known as a Graafian follicle which gradually enlarges and migrates towards the surface of the ovary. When it is fully ripe it bulges as a dome shaped protuberance from the surface of the ovary, measuring almost half an inch in diameter. The actual rupture of the follicle seems to be a natural conclusion to the gradual enlargement of the cyst-like swelling. The follicular fluid contained within the cyst is spilt into the abdominal cavity carrying the tiny delicate ovum into the fimbriated end of the Fallopian tube. The fimbria help to collect and guide the fluid and the ovum into the tube where fertilization takes place. The muscular wall of the Fallopian tube contracts and relaxes rhythmically so that fluid is drawn into it. The minute cells lining the inner surface contain specialized hair-like structures known as cilia which wave in unison and help to move fluid along.

The life of the unfertilized ovum lasts approximately 12 hours and if it has not been impregnated during this time it dies. Once dead it becomes fragmented and is absorbed by the cells lining the Fallopian tube.

Most women menstruate every 28 days and the standard menstrual cycle is, therefore, said to last for 28 days. The first day of the menstrual period is usually counted as day 1,. By this calculation a 5-day menstrual period lasts from day 1 to day 5 of the menstrual cycle. Ovulation usually occurs on the 14th day of a 2 8-day menstrual cycle, but ovulation is always geared to the next menstrual period and not to the menstrual period that has passed, and in fact always occurs about 14 days before the next menstrual period is due. Variations in this timing are not uncommon, but even so the range is usually between the 12th and the 16th day before the next menstrual period. Since the unfertilized ovum can only survive for about 12 hours, fertilization can only occur on the 14th day of a 2 8-day menstrual cycle. Sperms, however, can live in the female genital tract for 48 or even 72 hours. A woman who is ovulating on day 14 of a 28-day menstrual cycle should, therefore, have intercourse between day j 1 and day 14 if she is to become pregnant. It has been calculated, and it seems’reasonably Certain, that sperms travel from the cervix to the outer end of the Fallopian tube in less than one hour.

So called spurious or irregular ovulation may occur at any time during the menstrual cycle, but is rare. Even allowing for some variation from the usual it can be calculated from the above that fertilization is less likely if intercourse takes place during the first 8 days or during the last 10 days of a menstrual cycle, or conversely that pregnancy is possible if intercourse takes place between day 8 and day 18 of a 28-day cycle. This is the principle underlying the so-called ‘safe period’, or a rhythm method of contraception.

Any alteration of the menstrual cycle from the standard 28 days will, of course, also alter the safe period. Accurate calculation of the safe period during irregular menstrual cycles can be very complicated or indeed impossible. In a woman who has a 24-day menstrual cycle ovulation still occurs 14 days before the next period, that is on the 10th day of the cycle, and similarly a woman who has a 5-week (3 5-day) cycle ovulates on day 21 of that cycle.

Normal ovulation does not usually give rise to any symptoms, but minor discomfort does make some women aware that they have ovulated. Ovulation pain, known as ‘ Mittelschmerz’, may be felt in one side of the lower abdomen. This is probably caused by the rupturing of the Graafian follicle and may last for five minutes or for up to six hours and may vary in intensity from a very mild ache to quite a severe pain. Most women ovulate from each ovary alternately, but there are no hard and fast rules. The right ovary may ovulate for two, three or even six months in succession and then be followed for a similar length of time by the left ovary. Some women experience pain from only one ovary so that they are aware of ovulation in one side only on alternate months or for two or three consecutive months.

There is an increase in the secretion from the cervical glands at ovulation which may cause a colourless vaginal discharge that lasts for only one or two days and is not associated with any soreness or irritation. Some women also bleed from the uterus at the time of ovulation. This may take the form of a slight stain or it may become quite a pronounced blood loss which lasts for up to 48 hours, or even longer. This bleeding is more socially inconvenient than dangerous. Always seek medical advice if irregular bleeding occurs or if bleeding occurs between menstrual periods. Never assume that it is caused by ovulation unless it occurs exactly fourteen days before the next period and is small in quantity, but even so discuss this with your doctor in order to exclude any other possible cause.

The cells which line the Graafian follicle change after ovulation has occurred to form a structure known as the corpus luteum. The cells enlarge and assume first a pink, then a yellow colour. The function of the cells of the corpus luteum is the secretion of the hormone progesterone. A pregnancy is entirely dependent upon the corpus luteum during its early stages, but after fourteen weeks it becomes self-supporting and is capable of producing sufficient hormone from its own placenta to maintain a satisfactory environment for its survival within the uterus.

It is not known by what mechanism the ovaries decide which is going to function next. If one ovary is damaged, destroyed 01 removed the other ovary grows slightly larger and ovulates each month. Two ovaries are to a certain extent a luxury as well as an insurance. A woman can function perfectly well with only one ovary, since from this ovary she manufactures sufficient hormones and ova to remain just as fertile as if she had two.