Hormones are messengers that are present in all multicellular organisms – be they animal or plant organisms – that coordinate the functions of each part of that organism.
The sex hormones par excellence are oestradiol in females and testosterone in males. However, the adrenal glands in men and women produce both hormones and they are both necessary for normal development of the two sexes.
Oestradiol is responsible for sexual characteristics in women, for forming breasts and for initiating the menstrual cycle. It is produced in larger quantities during puberty and remains stable during a woman’s fertile years although the levels do vary across the menstrual cycle. It then decreases until it disappears completely during the menopause.
Some of its most important roles include:
- Ensuring that a single mature oocyte is formed during each menstrual cycle.
- Activating production of another hormone (luteinizing hormone or LH) that produces ovulation.
- Preparing the part of the uterus known as the endometrium for the embryo to nest and lead to pregnancy.
- Reducing the viscosity of cervical mucus in order to promote mobility of spermatozoa through it.
- Encouraging bone maturation (favouring growth in long bones and also mineralisation in bones).
Understanding levels of oestradiol in blood can be very useful because, amongst other things, it helps to:
- Diagnose certain types of tumours in the ovaries and testicles.
- Find the cause of abnormal development of male and female characteristics and detect premature puberty in girls.
- Estimate ovarian reserve when evaluated alongside other hormonal factors and an ultrasound scan of the ovaries. Anti-mullerian hormone has taken pride of place in this field over the last few years, however, since it can be taken at any time and is not subject to administration of contraceptives.
- Assess follicle (structures where the oocytes grow and mature) growth during ovarian stimulation in a course of assisted reproduction treatment.
Since oestradiol regulates so many different functions, it was developed as a drug many years ago. It can be used to treat typical symptoms of the menopause such as vaginal dryness, burn and irritation. It is also used to prevent osteoporosis in post-menopausal women and retrieve normal levels when it is not synthesised correctly either due to natural causes or due to ovarian failure. It is also present in some contraceptives and is routinely used during fertility treatment.