Erik
06-08-2009, 03:31 PM
What are estrogens?
Estrogen is often thought of as the “female sex hormone”, but in fact it occurs in both men and women.
There are actually a few forms of estrogen — the term usually refers to a family of steroid hormones that are synthesized in a variety of tissues.
* Estradiol (sometimes known as E2) is the most potent estrogen. In women it’s produced by the ovaries.
* Estriol (sometimes known as E3) is produced during pregnancy. Non-pregnant women don’t make much of it at all.
* Estrone (sometimes known as E1) is the most dominant estrogen in menopausal women.
Most often when people talk about “estrogen” they really mean estradiol. Estrone and estriol have about one tenth the potency of estradiol.
How our bodies make estrogens
Estrogens, like other sex hormones, are derived from cholesterol. They’re created by the aromatization (conversion) of androgens in an intricate process.
It’s easy to assume that so-called “male hormones” and “female hormones” are “opposites”. In fact, as the diagram below shows, the early stages of synthesizing estradiol and testosterone (and other androgens) are exactly the same!
Estradiol is formed if the substrate is testosterone, whereas estrone results from the aromatization of androstenedione.
In pre-menopausal women, the most important producer of estrogens are the ovaries. In post-menopausal women (whose ovaries have gradually ceased production), adipose (aka fat) tissue also plays a role. In men, the main source of estrogen is testosterone that has aromatized.
Because fat tissue can produce hormones, excess body fat can disrupt proper hormonal balance.
Regulating estrogen
So what signals estrogen release? Well, the hypothalamus secretes a hormone known as gonadotropin-releasing hormone (GnRH). GnRH regulates luteinizing hormone (LH) and follicle stimulating hormone (FSH) release from the pituitary gland. LH and FSH stimulate secretion of estrogen from the ovaries.
Estrogen is released in pulses at intervals of 1 to 3 hours.
Hormones can circulate in the body in both “bound” and “unbound” forms. Bound hormones are attached to something else, e.g. a transport protein such as sex hormone binding globulin (SHBG). (Imagine a bunch of kids hitching a ride on an inner tube as it’s pulled down a lazy river ride and you’ll get the idea.) Unbound hormones circulate freely.
Once released, only unbound estrogen appears to be biologically active.
Why are estrogens so important?
Estrogens are essential regulators of many major processes in the body. For example:
* They strongly influence the deposit of body fat — both amount and location.
* They also influence muscle mass.
* Estradiol has cardioprotective properties via changes in vasculature and other tissues. This is why premenopausal women have much lower rates of cardiovascular diseases than men — but their risk sharply increases after menopause.
* Estrogen acts on bone to determine the overall balance of breakdown and formation. Estrogen inhibits bone breakdown and may stimulate bone formation by initiating synthesis of IGF-1. After estradiol withdrawal during menopause (and with exercise induced amenorrhea in young female athletes) the pace of bone breakdown becomes limited, and mechanical loading is effective only in bones that are exposed to stress.
Estrogen is often thought of as the “female sex hormone”, but in fact it occurs in both men and women.
There are actually a few forms of estrogen — the term usually refers to a family of steroid hormones that are synthesized in a variety of tissues.
* Estradiol (sometimes known as E2) is the most potent estrogen. In women it’s produced by the ovaries.
* Estriol (sometimes known as E3) is produced during pregnancy. Non-pregnant women don’t make much of it at all.
* Estrone (sometimes known as E1) is the most dominant estrogen in menopausal women.
Most often when people talk about “estrogen” they really mean estradiol. Estrone and estriol have about one tenth the potency of estradiol.
How our bodies make estrogens
Estrogens, like other sex hormones, are derived from cholesterol. They’re created by the aromatization (conversion) of androgens in an intricate process.
It’s easy to assume that so-called “male hormones” and “female hormones” are “opposites”. In fact, as the diagram below shows, the early stages of synthesizing estradiol and testosterone (and other androgens) are exactly the same!
Estradiol is formed if the substrate is testosterone, whereas estrone results from the aromatization of androstenedione.
In pre-menopausal women, the most important producer of estrogens are the ovaries. In post-menopausal women (whose ovaries have gradually ceased production), adipose (aka fat) tissue also plays a role. In men, the main source of estrogen is testosterone that has aromatized.
Because fat tissue can produce hormones, excess body fat can disrupt proper hormonal balance.
Regulating estrogen
So what signals estrogen release? Well, the hypothalamus secretes a hormone known as gonadotropin-releasing hormone (GnRH). GnRH regulates luteinizing hormone (LH) and follicle stimulating hormone (FSH) release from the pituitary gland. LH and FSH stimulate secretion of estrogen from the ovaries.
Estrogen is released in pulses at intervals of 1 to 3 hours.
Hormones can circulate in the body in both “bound” and “unbound” forms. Bound hormones are attached to something else, e.g. a transport protein such as sex hormone binding globulin (SHBG). (Imagine a bunch of kids hitching a ride on an inner tube as it’s pulled down a lazy river ride and you’ll get the idea.) Unbound hormones circulate freely.
Once released, only unbound estrogen appears to be biologically active.
Why are estrogens so important?
Estrogens are essential regulators of many major processes in the body. For example:
* They strongly influence the deposit of body fat — both amount and location.
* They also influence muscle mass.
* Estradiol has cardioprotective properties via changes in vasculature and other tissues. This is why premenopausal women have much lower rates of cardiovascular diseases than men — but their risk sharply increases after menopause.
* Estrogen acts on bone to determine the overall balance of breakdown and formation. Estrogen inhibits bone breakdown and may stimulate bone formation by initiating synthesis of IGF-1. After estradiol withdrawal during menopause (and with exercise induced amenorrhea in young female athletes) the pace of bone breakdown becomes limited, and mechanical loading is effective only in bones that are exposed to stress.