Estrogens are a family of structurally related female sex hormones synthesized and secreted by cells in the ovaries and, in small amounts by cells in the adrenal cortex.
Androgens can be converted to estrogens peripherally, especially in fat tissue.
Three estrogens occur naturally in humans: estrone (El), estradiol (E2), and estriol (E3).
Of these, estradiol is the most biologically potent and the most abundantly secreted product of the ovary.
Estrogens are secreted throughout the menstrual cycle.
Two peaks occur: one before ovulation and one in the middle of the luteal phase.
Estrogens are transported in the blood bound to specific plasma globulins (which can also bind testosterone), inactivated and conjugated in the liver, and then excreted in the bile.
Estrogens are necessary for the normal female physical maturation.
In concert with other hormones, estrogens provide for the reproductive processes of ovulation, implantation of the products of conception, pregnancy, parturition, and lactation by stimulating the development and maintaining the growth of the accessory organs.
In the absence of androgens, estrogens stimulate the intrauterine development of the vagina, uterus, and uterine tubes from the embryonic mullerian system.
They also stimulate the stromal development and ductal growth of the breasts at puberty, are responsible for the accelerated pubertal skeletal growth phase and for closure of the epiphyses of the long bones, contribute to the growth of axillary and pubic hair, and alter the distribution of body fat to produce the typical female body contours, including the accumulation of body fat around the hips and breasts.
Larger quantities of estrogen stimulate pigmentation of the skin in the nipple, areolar, and genital regions.
In addition to their effects on the' growth of uterine muscle, estrogens play an important role in the development of the endometrial lining.
During anovulatory cycles, continued exposure to estrogens for prolonged periods leads to abnormal hyperplasia of the endometrium and abnormal bleeding patterns.
When estrogen production is poorly coordinated during the normal menstrual period, inappropriate bleeding and shedding of the endometrium also can occur.
Estrogens have a number of important extragenital metabolic effects.
They are responsible for maintaining the normal structure of skin and blood vessels in women.
Estrogens decrease the rate of bone resorption by antagonizing the effects of parathyroid hormone on bone; for this reason, osteoporosis is a common problem in estrogen-deficient postmenopausal women.
In the liver, estrogens increase the synthesis of transport proteins for thyroxine, estrogen, testosterone, and other hormones.
Estrogens also affect the composition of the plasma lipoproteins.
They produce an increase in high-density lipoproteins (HDLs), a slight reduction in low-density lipoproteins (LDLs), and a reduction in cholesterol levels.
Estrogens have additional cardioprotective actions, including direct anti-atherosclerotic effects on the arterial wall (augmentation of vasodilating and anti platelet aggregation factors such as nitric oxide and prostacyclin), vasodilation through endothelium-independent mechanisms, antioxidant activity, reduced levels of angiotensin-converting enzyme and renin, reduction of homocysteine levels, improved peripheral glucose metabolism with subsequent decreased circulating insulin levels, and direct effects on cardiac function (i.e., increased left ventricular diastolic filling and stroke volume output).
Estrogens increase plasma triglyceride levels and they enhance the coagulability of blood by effecting increased circulating levels of plasminogen and factors II, VII, IX, and X.
Estrogens appear to have both neurotropic and neuro-protective effects on cognitive function and memory.
Studies indicate possible prevention of Alzheimer's disease through anti-inflammatory mechanisms to prevent vascular injury, increased cerebral blood flow, and altered brain activation.
Estrogens promote dendritic branching and enhance presynaptic and postsynaptic signal transmission through increased production of neurotransmitters and receptors.
The estrogens cause moderate retention of sodium and water.
Most women retain sodium and water and gain weight just before menstruation.
This occurs because the estrogens facilitate the movement of intravascular fluids into the extracellular spaces, producing edema and increased sodium and water retention by the kidneys because of the decreased plasma volume.
Referrence:Female Internal Genitalia||Estrogens(Chinese Version)