a highway) for the sperm to reach the egg and for the embryo to reach the uterus (see figure 2.3). The process of fertilization takes place in the upper third of the Fallopian tubes, so the sperm have to be robust enough to be propelled from the uterus up two-thirds of the Fallopian tube to fertilize the egg. Contractions in the uterine muscle during orgasm are believed to assist this process.
The Fallopian tube enlarges at ovulation and secretes fluids as it responds to oestrogens. At midcycle, the fluid is copious, alkaline and contains nutrients, gases, proteins, electrolytes and steroids.7
ENDOCRINE COMMUNICATION
How does the body know when the embryo is entering the womb? The womb must have a precise line of communication to the ovary, where the eggs are manufactured and released. This is accomplished by endocrine communication. The pituitary and ovaries communicate with each other by sending ‘chemical messengers’ (hormones) through the blood system to tell each other what to do and when. Light hitting the retina of the eye stimulates the pituitary and hypothalamus, which releases GnRH, a hormone that triggers the release of LH from the pituitary. The LH surge causes the follicle membrane to rupture, releasing the egg. Ovulation occurs if the ovum meets a sperm in the Fallopian tube, and the follicle seals up to form a corpus luteum. This begins to produce progesterone to make the endometrium ready for implantation of the fertilized egg. Progesterone is produced by the corpus luteum until the third month of pregnancy, when the placenta is sufficiently mature to take over. If no fertilized embryo is implanted, the corpus luteum is reabsorbed into the ovary and the whole process begins all over again.8 The major hormones involved in the reproductive system are listed in table 2.1.
Table 2.1
The major reproductive hormones of the menstrual cycle
| ORGAN | HORMONE | ACTION |
| Hypothalamus | Gonadotrophin-releasing hormone (GnRH) | Stimulates the pituitary gland to produce FSH and LH |
| Anterior pituitary | Follicle-stimulating hormone (FSH) | Stimulates ovarian follicles |
| Luteinizing hormone (LH) | Initiates ovulation | |
| Prolactin | Stimulates lactation | |
| Posterior pituitary | Oxytocin | Stimulates uterine contraction |
| Ovary | Oestrogen | Stimulates endometrial growth and uterine contractions |
| Progesterone | Maintains pregnancy | |
| Uterus | Prostaglandins (PGE/PGF) | Stimulates uterine contractions, menstrual pain and birth |
Establishing the correct levels of these hormones is the key to getting the right message to the right place at the right time. When we say that the hormones are ‘out of balance’, the wrong messages are being sent and received, and things can begin to go awry.
FOLLICLE-STIMULATING HORMONE (FSH)
1 FSH is responsible for maturation of the ova in the follicle. Once a dominant follicle emerges with a diameter of 6.5–14mm, the rest will subside.
2 FSH production is inhibited by excess oestrogen and inhibin.
3 FSH causes granulosa cells to multiply rapidly and produce oestradiol.
4 Normal levels of FSH are 5–20mU/ml, depending on the day of the test.
5 When FSH levels are over 20mU/ml, menopause may be due within five years. Women with elevated FSH can still get pregnant as other factors, such as stress, can raise levels. After IVF treatments, where the ovaries have been hyperstimulated, many women find they have abnormal FSH levels for a time. Menopause is usually indicated with FSH levels of 40–200mU/ml.
LUTEINIZING HORMONE (LH)
1 LH secretion precedes ovulation and completes the maturation of the ovarian follicle.
2 LH stimulates androgen (testosterone) production.
3 LH is inhibited by oestrogen except just before ovulation, when it surges.
4 Progesterone may block LH secretion as it decreases the rate at which LH is pulsed from the pituitary gland.
5 LH receptors inside the granulosa cells develop as a result of FSH and oestrogen build up.
6 When LH surges, the dominant follicle grows between 1.4–2.2mm per day, reaching a maximum diameter of 18–22mm, and is ready for ovulation. It should be fully mature on day 14–16 of the menstrual cycle.
7 The interval between the LH surge and ovulation is 37–38 hours. Ovulation occurs randomly from left to right ovaries during natural cycles.
8 The Fallopian tubes enlarge at ovulation and secrete fluids as they respond to oestrogen and the LH surge.
9 Normal levels of LH are 7–14U/ml. While LH remains normal, ovulation is possible. FSH tests alone are not indicative of perimenopause as they can fluctuate wildly at this time. As LH levels rise abruptly at menopause, they should be tested with FSH.
PROLACTIN
1 This hormone inhibits ovulation.
2 Elevated prolactin can also be caused by high melatonin levels, resulting in decreased fertility (melatonin from the pineal gland increases when the eye registers darkness).
3 Excess prolactin can be caused by drugs such as tranquillisers, anti-ulcer drugs, high-dose oestrogen oral contraceptive pills, alcohol and street drugs.
4 Hypothyroidism and breast stimulation may also increase prolactin levels.
5 When prolactin is high, GnRH and LH are lowered. This can cause menstruation and ovulation to stop.
RELAXIN
1 This protein-based hormone, produced by the corpus luteum of the ovary, is similar to insulin and growth hormone.
2 It softens tissues and muscles, and may be responsible for morning sickness during pregnancy.
THE REPRODUCTIVE CYCLE
The bottom line of the reproductive system is to make a healthy bouncing baby through the processes of sexual intercourse, conception and pregnancy. One of the more formidable tasks of the female reproductive system is to prepare the lining of the womb (the endometrium) to feed and nurture the embryo. However, it is not possible for the body to maintain the endometrium in a continuous, heightened ‘ready state’ for pregnancy. Thus the body follows a monthly cycle of slowly building up the endometrium so that it will be in a nutrient-rich state only when a fertilized embryo may be around. Think of the endometrium as fresh food for the embryo; if it gets old (past its sell-by date) it is less nutritious and is less likely to sustain the pregnancy. This ‘food for the fetus’ is renewed each month, so the quality of food you eat is crucial to the health of this tissue. If a fertilized egg fails to appear, then the body flushes away the existing endometrium, and starts all over again. This flushing away of the endometrium is, of course, the menstrual period.
THE MENSTRUAL CYCLE
The menstrual cycle in most women lasts approximately 28 days, with the first day of blood flow (the menstrual period) usually designated as day 1 of the cycle (see figures 2.2 and 2.4). Around day 1 the hypothalamus secretes gonadotrophin-releasing hormone (GnRH) and, in response to this hormone, the pituitary gland secretes increasing amounts of FSH (follicle-stimulating hormone). FSH stimulates the granulosa cells (helper cells) in each follicle to ensure that each ova is ‘fed’ nutrients to help it produce oestrogen and to stimulate the egg to mature.9 Oestrogen also sends a message to the womb to tell it to produce more endometrial cells, so that a healthy thickened endometrium will be present to accept the egg should it be fertilized by a sperm in the Fallopian tubes. Unfortunately, oestrogen also has some bad effects. It is responsible for the water retention between cells, which is why some women can feel bloated before a period, and for stimulating uterine contractions (menstrual cramps).
When the follicle reaches 15–17mm in diameter (around day 14–15 of the cycle),