Estradiol in the circulation is bound to sex hormone binding globulin and albumin. In the liver, estrogens are conjugated to sulfate or glucuronate to make them water soluble after which they are excreted in the bile and reabsorbed prior to leaving the body via the urine. The normal development and maturation of the female is dependent on estrogens. Besides stimulating development of the reproductive structures and secondary sexual characteristics, estrogens are necessary to the cyclic endometrial changes necessary for reproduction, development of the breasts , health of the skin and vascular system and bone homeostasis. Estrogen also affects intestinal motility, blood coagulation, cholesterol metabolism, female libido, and sodium and water conservation by the kidneys .
Estrogens increase the uterine muscle mass, excitability and responsiveness to oxytocin .
FSH secretion is negatively inhibited by estrogens, but LH may be either positively or negatively affected dependent on the hormonal milieu. Estrogens have an anabolic effect and have been used in animal husbandry to increase the weight of domestic animals. Estrogens increase libido in humans and are responsible for estrous behavior in animals. Plasma cholesterol is lowered by estrogens which are protective against atherosclerotic disease . In childhood, the blood concentration of sex hormones is very low.