# Oestrogen Physiology

> Oestrogen physiology in MBBS Physiology: two-cell synthesis, cycle levels, feedback switch, bone protection and menopausal changes.

- Canonical URL: https://prepelephant.com/topics/mbbs/physiology/oestrogen-physiology
- Exam / course: MBBS · Subject: Physiology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Oestrogen Physiology", PrepElephant, https://prepelephant.com/topics/mbbs/physiology/oestrogen-physiology

## Direct answer

Oestradiol-17β, the most potent natural oestrogen, is made in the ovarian follicle by a two-cell partnership: LH drives theca cells to produce androgens, which diffuse to granulosa cells where FSH-induced aromatase converts them to oestradiol. Levels trace the follicular story — early follicular phase around 30-50 pg/mL, a preovulatory surge of 200-500 pg/mL just before the LH peak, a luteal-phase plateau near 100-200 pg/mL, and after menopause a fall below 20 pg/mL while FSH rises above 30-40 mIU/mL. Oestrogen proliferates the endometrium, builds the secondary sexual characteristics, protects bone by restraining osteoclastogenesis (via RANKL suppression), raises HDL and lowers LDL, increases clotting factors, and induces hepatic SHBG synthesis — the last explaining why combined pills improve acne and hirsutism. Its feedback is biphasic: negative on the pituitary through most of the cycle, switching to positive feedback above a sustained threshold of roughly 200 pg/mL for about 48 hours to trigger the LH surge — the switch oral contraceptives abolish.

## What you must remember

- **Two-cell, two-gonadotrophin theory:** theca (LH, androgens) plus granulosa (FSH, aromatase) equals oestradiol — the standard diagram every examiner asks you to draw.
- **Potency order:** oestradiol (E2) strongest, oestrone (E1) intermediate, oestriol (E3) weakest and mainly placental — E3 serves as a foetal wellbeing marker.
- **Cycle numbers:** early follicular 30-50 pg/mL, preovulatory peak 200-500, luteal 100-200 pg/mL; menopausal oestradiol below 20 with FSH above 30-40 mIU/mL and 12 months of amenorrhoea — the diagnostic set.
- **Feedback switch:** sustained oestradiol near 200 pg/mL for about 48 hours converts negative to positive feedback, generating the mid-cycle LH surge; progestogens from the corpus luteum then hold subsequent FSH recruitment down.
- **Bone physiology:** oestradiol suppresses osteoclast differentiation (less RANKL, more osteoprotegerin) and limits cytokine-driven resorption — postmenopausal loss is fastest in trabecular bone (spine, wrist) in the first 5-10 years at 2-5 per cent yearly.
- **Metabolic and hepatic effects:** HDL up, LDL down, but factors II, VII, VIII, X and fibrinogen up (the venous thromboembolism risk of oestrogen-containing contraceptives); SHBG induction lowers free testosterone — the therapeutic logic in polycystic ovary syndrome.
- **Puberty sequence:** thelarche (breast bud, oestrogen-driven) is the first sign, then adrenarche, then the growth spurt — girls gain about 25 cm, and oestrogen finally fuses the epiphyses, which is why precocious puberty costs final height.
- **Placental and male roles:** oestriol from the foeto-placental unit; in men, aromatised oestradiol guards bone and epiphyseal timing.

## A worked case across the reproductive arc

A 13-year-old develops breast buds — thelarche — with a growth spurt following: follicular oestradiol proliferates the ducts and stroma, the spurt rides oestrogen-growth hormone synergy, and the same hormone will later fuse the epiphyses and cap her height. Mid-cycle, her oestradiol crosses the sustained 200 pg/mL threshold, feedback flips positive, the LH surge fires, and ovulation follows within 12-24 hours — the physiology every calendar method tries to track.

Skip forward forty years: the follicular pool is exhausted, oestradiol sits under 20 pg/mL, and lost negative feedback drives FSH above 40 — hot flushes, accelerated bone loss, urogenital atrophy. Hormone replacement controls symptoms and conserves bone, though long-term use carries breast-cancer and thromboembolism signals — modern prescribing uses the lowest effective dose for the shortest appropriate duration.

## Where students slip

Students name the granulosa cell as the sole source of oestradiol; it is a duet — theca under LH makes the androgen substrate, granulosa under FSH aromatises it — and the theca's LH dependence is why luteinising hormone matters even before ovulation. The second slip is forgetting the feedback flip: oestrogen is not a simple negative-feedback hormone, and the sustained-threshold positive feedback (about 48 hours near 200 pg/mL) is the mechanism oral contraceptive pills precisely prevent — suppress the surge and you suppress ovulation. Third, students attribute menopausal bone loss to calcium deficiency; it is oestrogen-deficient osteoclast release, fastest in trabecular bone — which is why spine and wrist fractures present first, and why the answer "alendronate or HRT," not "calcium alone," is the correct exam response.

## Frequently asked questions

### How is oestradiol synthesised in the ovarian follicle?

By the two-cell theory: LH-stimulated theca cells produce androstenedione, which granulosa cells convert to oestradiol using FSH-induced aromatase — both gonadotrophins are required.

### What plasma oestradiol pattern defines a normal menstrual cycle?

Early follicular 30-50 pg/mL, a preovulatory peak of 200-500 pg/mL, a luteal plateau of 100-200 pg/mL, and baseline just before menses — tracked with LH and FSH in infertility work-ups.

### How does oestrogen feedback switch from negative to positive?

Sustained oestradiol near 200 pg/mL for about 48 hours in the late follicular phase converts pituitary feedback to positive, generating the mid-cycle LH surge that triggers ovulation.

### Why does bone loss accelerate after menopause?

Oestrogen deprivation releases osteoclastogenesis from RANKL suppression — trabecular resorption runs 2-5 per cent yearly in the early postmenopausal years, driving vertebral and wrist fractures.

### Which coagulation changes do oestrogen-containing contraceptives cause?

Hepatic induction of factors II, VII, VIII, X and fibrinogen raises venous thromboembolism risk — the reason for screening for thrombophilia history and preferential progestogen-only methods in at-risk women.