In the female, estradiol acts as a growth hormone for tissue of the reproductive organs, supporting the lining of the vagina, the cervical glands, the endometrium, and the lining of the fallopian tubes. It enhances growth of the myometrium. Estradiol appears necessary to maintain oocytes in the ovary.
During the menstrual cycle, estradiol that is produced by the growing follicle triggers, via a positive feedback system, the hypothalamic-pituitary events that lead to the luteinizing hormone surge, inducing ovulation. In the luteal phase estradiol, in conjunction with progesterone, prepares the endometrium for implantation.
During pregnancy, estradiol increases due to placental production. In baboons, blocking of estrogen production leads to pregnancy loss, suggesting that estradiol has a role in the maintenance of pregnancy.
Research is investigating the role of estrogens in the process of initiation of labor.
The development of secondary sex characteristics in women is driven by estrogens, to be specific, estradiol. These changes are initiated at the time of puberty, most enhanced during the reproductive years, and become less pronounced with declining estradiol support after the menopause. Thus, estradiol enhances breast development, and is responsible for changes in the body shape, affecting bones, joints, fat deposition. Fat structure and skin composition are modified by estradiol.
The effect of estradiol (and estrogens) upon male reproduction is complex. Estradiol is produced in the Sertoli cells of the testes. There is evidence that estradiol is designed to prevent apoptosis of male sperm cells.
Several studies have noted that sperm counts have been declining in many parts of the world and it has been postulated that this may be related to estrogen exposure in the environment. Suppression of estradiol production in a subpopulation of subfertile men may improve the semen analysis.
Males with sex chromosome genetic conditions such as Klinefelters Syndrome will have a higher level of estradiol.
There is ample evidence that estradiol has a profound effect on bone. Individuals without estradiol (or other estrogens) will become tall and eunuchoid as epiphysieal closure is delayed or may not take place. Bone structure is affected resulting in early osteopenia and osteoporosis.
Also, women past menopause experience an accelerated loss of bone mass due to a relative estrogen deficiency.
Estradiol has complex effects on the liver. It can lead to cholestasis. It affects the production of multiple proteins including lipoproteins, binding proteins, and proteins responsible for blood clotting.
Estrogens can be produced in the brain from steroid precursors. As antioxidants, they have been found to have neuroprotective function.
The positive and negative feedback loop of the menstrual cycle involve ovarian estradiol as the link to the hypothalamic-pituitary system to regulate gonadotropins.
Estrogen is considered to play a significant role in women’s mental health, with links suggested between the hormone, mood and well-being.
Sudden drops or fluctuations in, or long periods of sustained low levels of estrogen may be correlated with significant mood-lowering. Clinical recovery from depression postpartum, perimenopause, and postmenopause was shown to be effective after levels of estrogen were stabilized and/or restored.
Estrogen affects certain blood vessels. Improvement in arterial blood flow has been demonstrated in coronary arteries.
Estrogen is suspected to activate certain oncogenes, as it supports certain cancers, notably breast cancer and cancer of the uterine lining. In addition, there are several benign gynecologic conditions that are dependent on estrogen, such as endometriosis, leiomyomata uteri, and uterine bleeding..
The effect of estradiol, together with estrone and estriol, in pregnancy is less clear. They may promote uterine blood flow, myometrial growth, sitmulate breast growth and at term, promote cervical softening and expression of myometrial oxytocin receptors.
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