Estrogen is a female sex hormone that is produced in the ovaries and, to a lesser degree, in the adrenal glands and adipose tissues. It is essential for the development of primary and secondary sex characteristics, as well as function of the reproductive organs. Estrogen also plays a role in several other processes, including bone metabolism and liver function. While ovarian insufficiency, aromatase deficiency, and hyperprolactinemia result in pathologically low estrogen levels, a decrease in estrogen is a normal feature of menopause. Possible symptoms of estrogen deficiency include menopausal symptoms, vaginal and endometrial atrophy, and osteoporosis. Increased estrogen levels may also have adverse effects, including gynecomastia, thrombosis, and an increased risk of breast and endometrial cancer.
Ovarian estrogen synthesis
- LH stimulates androgen synthesis in ovarian theca cells.
- FSH stimulates conversion of androgens to estrogens.
- Conversion of androgens to estrogens is catalyzed by the aromatase enzyme.
Extra-ovarian estrogen synthesis 
- Potency: estradiol > estrone > estriol
- During pregnancy, estrogen concentration increases.
- When estrogen binds to its receptor in the cytoplasm, a hormone-receptor complex is formed that translocates to the nucleus.
Measurement of unconjugated estriol (uE3 or free estriol) is part of the prenatal screening for fetal anomalies (i.e., triple screen test and quad screen test). Decreased levels are associated with Down syndrome, Edward syndrome, molar pregnancy, and fetal demise.
- Cervix 
- Vagina: proliferation of epithelium
- Pubis: hair growth
- Breast: breast growth
Extragenital tissue 
- Bones: ↑ Bone formation by inhibiting bone resorption (induces osteoclast apoptosis)
- Blood vessels: protective effect against atherosclerosis
- Blood clotting: ↑ Risk of thrombosis
- Kidneys: ↑ Water and sodium retention (may contribute to edema)
- Protein synthesis
- Adipose tissue: female distribution of adipose tissue
- ↑ Cancer risk
- Spider nevi, gynecomastia, and testicular atrophy in individuals with cirrhosis
- Breast hypertrophy, gynecomastia (in men), galactorrhea
- Weight gain (edema)
- Liver toxicity 
- Nausea and vomiting
- Depressive moods
- Definition: a condition of increased circulating estrogen
- Both sexes: palmar erythema, spider telangiectasias
- Definition: a condition of decreased circulating estrogen
- Clinical features