The hormone estrogen coordinates reproduction and stimulates the development and maintenance of female characteristics, notes the National Cancer Institute. Estrogen promotes changes in the breast, uterus, brain, bone, liver and heart. Not all estrogen hormones are produced by the body, however, and estrogen-like compounds can also be found in some plants and industrial chemicals, plastics, pollutants and pesticides.
Ovarian Production
The collective term "estrogen" actually refers to three substances: estradiol, estrone and estriol. During the fertile years of a woman's life, the majority of estrogen she produces is estradiol, which comes from the ovaries. From the time of puberty, an intricate pathway between the brain and the ovaries becomes active, signaling the development of potential eggs, known as follicles, and the resultant production of estrogen. This pathway is known as the hypothalamic-pituitary axis. At the base of the brain, the hypothalamus secretes hormones that change the levels of the pituitary hormones, follicle stimulating hormone (FSH) and leutinizing hormone (LH). FSH is responsible for the maturation of an undeveloped follicle. The follicle encases the egg, which upon ovulation becomes the collaborative partner to the sperm in the creation of a fetus. As levels of FSH increase during the follicular phase, or first 14 or so days of the cycle, it stimulates an increased production of estrogen in the cells of the developing follicle. Menstruation, or the onset of bleeding, marks the beginning of the menstrual cycle and follicular phase.
Aromatization
A second source of estrogen is formed in the conversion of estrogen from its precursor hormones. These precursor hormones include the androgens testosterone and DHEA, and 17-alphaOH-pregnenolone which is directly sourced from the adrenal glands. This type of estrogen is known as estrone. Post-menopausal women derive almost all of their estrogen in the form of estrone from this conversion. Although estradiol is the primary estrogen in menstruating women, a small portion of the total estrogen level is in the form of estrone as well. The enzyme that promotes this conversion is known as 5-alpha reductase, or the "aromatase enzyme."
Sperm
The conversion process from estradiol to estroneto is known as aromatization or peripheral conversion. As the ovaries are not the primary source for estrone in women, the conversion is known as peripheral because it takes place in distant sites such as the hair follicles, skin, brain, bone, bone marrow, muscle and fat tissue. Interestingly, immature sperm, known as spermatids, have the 5-alpha reductase enzyme and produce estrogen within the epididymis of the male testes.
Placenta
Estriol, the third form of estrogen, is the weakest. Estriol is found in its highest amount during pregnancy in the placenta, where estriol is converted from the androgen DHEA, according to DirectLabs.com. However, the androgen source does not come from the mother, but rather the fetus.
Liver Metabolism
The liver is responsible for the production of the estrogen metabolite estriol. "Medical Biochemistry" notes that estrone is metabolized by the liver into three pathways, one of which is to estriol. The estriol route is considered the most significant because estriol is the major source of estrogen that's removed from the body in urine.
References
- National Cancer Institutes: Understanding Cancer Series: Estrogen Receptors/SERMs
- Direct Labs: Estriol
- Environmental Health Perspectives: Sperm, a source of estrogens
- "Medical Biochemistry"; N.V. Bhagavan; 2002
- "Women, Hormones & the Menstrual Cycle"; Ruth Trickey; 2003
