Major estrogen in normal adult women is –
**Core Concept**
Estrogen plays a crucial role in the reproductive and sexual health of women, influencing the menstrual cycle, pregnancy, and menopause. In adult women, estrogens are produced primarily by the ovaries, with a smaller contribution from the adrenal glands and peripheral tissues.
**Why the Correct Answer is Right**
Estriol is the major estrogen in pregnancy, but in non-pregnant women, the major estrogen is Estradiol (E2). Estradiol is produced by the ovarian stroma and theca cells in the ovaries, where it is synthesized from cholesterol through the action of aromatase enzyme. Aromatase converts androstenedione into estrone, which is then converted to estradiol by the enzyme 17β-hydroxysteroid dehydrogenase. Estradiol exerts its effects through binding to estrogen receptors (ERα and ERβ), influencing gene expression and regulating various physiological processes.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Estrone (E1) is the major estrogen in postmenopausal women, not in normal adult women. Estrone is produced by the peripheral conversion of androstenedione in adipose tissue.
**Option B:** This option is incorrect because Estriol (E3) is primarily produced during pregnancy, where it is synthesized from estradiol and estrone by the placenta. It is not the major estrogen in normal adult women.
**Option C:** This option is incorrect because there is no commonly recognized estrogen by this name in the human body.
**Clinical Pearl / High-Yield Fact**
Estradiol plays a crucial role in maintaining bone density, and its deficiency can lead to osteoporosis, particularly in postmenopausal women. This is why estrogen replacement therapy is often prescribed to prevent osteoporosis in postmenopausal women.
**Correct Answer: D. Estradiol**