Estrogens are a group of steroid hormones derived from cholesterol. They include estradiol, estrone and estriol. Intriguingly, the male sex hormone testosterone is an intermediate in the synthesis of estrogens, and the structures of the two hormones are quite similar. The main difference is an extra methyl group on testosterone. Steroid hormones such as estrogen can diffuse freely through the plasma membrane. The estrogen receptor is located in the nucleus, and when estrogen binds, the receptor activates the estrogen response element.
Estrogen is responsible for the major sexual developments of the female body during puberty. It is first responsible for the female growth spurt, and then it acts to enlarge the uterus, ovaries, and other reproductive system features so that the body can support a pregnancy. Estrogens are also responsible for the development and enlargement of the breasts, an increase in fatty deposits in the subcutaneous layer, growth of the pelvis, growth of armpit and pubic hair, and other minor metabolic effects.
Between puberty and menopause, the female body enters the menstrual cycle. Rising and falling estrogen levels play a key role in this cycle. At the beginning of the cycle, follicle stimulating hormone (FSH) and luteinizing hormone (LH) stimulate the follicle in the ovary to begin producing estrogen, which inhibits the release of FSH and LH from the pituitary gland, although they are still being produced. At a critical concentration, however, estrogen stimulates the release of the stored FSH and LH, and the sudden hormone burst results in ovulation, or the release of the egg from the follicle. At the end of the cycle, as FSH and LH levels drop, estrogen levels also drop, and the loss of hormones results in menstruation if the egg has not been fertilized.
Although estrogens provide many positive benefits for the female body, certain forms of breast cancer actually use estrogen as a growth hormone. Treatments designed against these types of cancer are meant to slow estrogen production. The estrogen receptor is also a tempting target for treatments.
During menopause, the female body stops producing progesterone and produces less estrogen, which is the reason that the menstrual cycle stops. The loss of hormones, however, also causes such feared symptoms as osteoporosis, night sweating, hot flashes, and vaginal itching and dryness, which also results in pain during intercourse. Hormone replacement treatment has always been the easy answer for women suffering from worse-than-normal symptoms, but a 2002 study indicated that the therapy can increase the risk of heart problems and breast cancer.