Estradiol is a female sex hormone produced by the ovaries, adrenal gland and also the placenta during pregnancy. Estradiol is the most important hormone during a female’s reproductive years, and is required for reproductive and sexual function as well as having an impact on the health of other organs and tissues.
Some of the functions of estradiol include:
Female reproductive growth
In females, estradiol acts primarily as a growth hormone for the reproductive organs including the vagina, the fallopian tubes, the endometrium and the cervical glands. Estradiol also enhances growth of the womb’s muscle layer, the myometrium. In addition, the hormone maintains oocytes (eggs in the ovary) and triggers a series of events that lead to ovulation.
Development of secondary sexual characteristics
The changes that begin around puberty are driven by estradiol. These changes are enhanced during the reproductive age and then become less pronounced after the menopause, as estradiol levels decline. Estradiol is required for normal breast development, alteration of body shape, skin changes, and the fat distribution profile that is typical of females. Estradiol in males is produced by the Sertoli cells of the testes.
Estradiol during menstrual cycle
Estradiol is needed to maintain the eggs inside a female’s ovaries. During the menstrual cycle, follicles on the ovaries secrete estradiol, which triggers a series of events that lead to a surge in luteinizing hormone and, in turn, induces ovulation. This phase of the cycle is referred to as the follicular phase. After ovulation, during the luteal phase, estradiol works in conjunction with progesterone to prepare the womb lining for implantation.
Estradiol during pregnancy
During pregnancy, the estradiol level rises because it is also produced by the placenta. Estradiol is also thought to play a role in maintaining the pregnancy and research is currently ongoing into the role of estrogens in initiating labor.
Estradiol in bone health
A healthy estradiol is also needed to support adequate bone growth and maintain the health of bones and joints. Estradiol also has an impact on bone structure and oteopenia and osteoporosis can occur if levels of this hormone are low. Bone loss can be accelerated in women of post-menopausal age, who may have a relative deficiency in estradiol.
Effects on the brain
Estradiol is also produced in the brain and estrogens have been shown to have neuroprotective effects.
Effects on blood flow
Estrogens can exert effects on the vasculature and have been shown to improve blood flow in the coronary arteries.
Involvement in disease
Some research suggests that estrogen activates certain cancer causing genes called oncogenes that raise the risk of breast cancer and endometrial cancer. Estrogens are also involved in several non-cancerous conditions including endometriosis, uterine fibroids and uterine bleeding.