Oestregen (also spelled Estrogen) is a group of compounds, that act as the primary female sex hormone. The name oestrogen is derived from ‘oistros’ meaning the fertility period of female and ‘gonos’ means to generate.Natural oestrogens are steroid hormones. The main function of Oestrogen is to mantain and regulate menstruation cycle and oestrous or reproductive cycle in woman. Oestrogen also helps in other physiological functions like temperature regulations, controlling bone density etc. Oestrogens are synthesized in the theca interna cells present in the ovary and are released by the follicles on the ovaries by the stimulation of Luteinizing hormone (LH), that is secreted from anterior pituitary gland. Oestrogen is secreted by the corpus luteum after the egg has been released from the follicle. Besides ovary some estrogens are also produced in smaller amounts by liver, adrenal glands, and the breasts.

Biosynthesis of oestrogen : As stated above, biosynthesis of oestrogen starts in theca interna cells in the ovary. The first step of oestrogen synthesis is the synthesis of androstenedione from cholesterol. Androstenedione is the precursor of testosterone and estrogen. While crossing the basal membrane into the surrounding granulosa cells, androstenedione either immediately convert into estrone (catalyzed by the enzyme aromatase), or into testosterone and then estradiol. Androstenedione is converted to testosterone in presence of the enzyme 17β-hydroxysteroid dehydrogenase, testosterone then further converted into estradiol in presence of aromatase.

Types of oestrogen : There are three natural oestrogens namely estrone (E1), estradiol (E2), and estriol (E3).

Oestrone : Oestrone is the least abundant oestrogen and it is predominant during menopause. The molecular formula of estrone is C18H22O2 and the structural formula is

Oestradiol : Oestradiol is the predominant estrogen during reproductive years i.e. non-pregnant females who are between the menarche and menopause and it is strongest among the three oestrogens. Oestradiol is about 80 times as potent as estriol and 10 times as potent as estrone. The molecular formula of Oestradiol is C18H24O2 and the structural formula is

Oestriol : Oestriol remain predominant during pregnancy. The molecular formula of oestriol is C18H24O3 and the structural formula is

Another kind of oestrogen called Estetrol (E4) found in maternal serum at around 20 week of pregnancy.

There are some non steroidal compounds that also possess estrogenic activity. These are xenoestrogens (artificial oestrogen ), phytoestrogens (produced by plants ), mycoestrogens (produced by fungi).

Functions of oestrogen : Oestrogen enters all cells but the response of oestrogen depends on the presence of oestrogen receptor (dimeric nuclear protein ) in the particular cell. Generally ER is expressed in female sex organs like ovary, uterus and breasts. Oestrogen enters passively in the target cells and bind with the estrogen receptor and then activate the transcription of target genes.

The primary functions of oestrogen are development of female secondary sex characteristics (development of breasts, growth of underarm and pubic hair, widening of hips and distribution of fats around buttocks and thigh) maintaining menstruation cycle and oestrous cycle (thickening of the endometrium, thickening of the vaginal wall, increased uterine growth and increased vaginal lubrication). Oestrogen with Progesteron prepare uterus for pregnancy and the development of the foetus. Hike in oestrogen level induce the release of Lutenising hormone, that triggers the release of ovum from Graafian follicle in the ovary.

Other functions of oestrogen include as follows:

  1. Increase or preservation of bone formation
  2. Increase vaginal lubrication and estrogenization of vaginal mucosa
  3. Increase adhesiveness of the platelates
  4. Increase in the level of High Density lipoproteins and triglyceride and decrease Low Density Lipoproteins
  5. Reduce bowel movement
  6. Increase of cholesterol in bile
  7. Maintaining maintain healthy libido
  8. Stimulating collagen in the skin

It is found that oestrogen plays an important role in mental health of women. Withdrawal of oestrogen or fluctuation in oestrogen level or menopause (decrease in oestrogen level) may cause depression, mood swing and anxiety.

Medical Application of oestrogen :

Contraceptives : Synthetic oestrogen with synthetic progestin used as oral contraceptives. These hormones togather gave negetive feedback to supress the release of luteinizing hormone and follicle stimulating hormone, the gonadotrophins that are necessary for ovulation thus preventing pregnancy. Moreover progestin inhibits the penetration of sperm through the cervix into uterus and fallopian tubes.

Hormone Replacement Therapy : The production of oestrogen drop significantly after menopause or hysterectomy. Due to the decreased level of oestrogen many women suffers from various physical and mental problems like hot flushes, night sweat, vaginal dryness, mood swing, depression etc. To mange this problem oestrogen is given externally to restore normal level of the said hormone. Oestrogen may given as tablets, skin patches or gels.