Uterus Histology
On this page
Direct answer
Nowhere else in the body does a lining demolish and rebuild itself each month, and uterine histology is the record of that cycle. The endometrium has two layers: the stratum functionalis — glands, stroma and the spiral arteries that supply it — which sheds at menstruation, and the stratum basalis, retained along the muscularis mucosae, whose straight basal arteries and glandular remnants regenerate the surface. Under oestrogen the proliferative endometrium grows straight, tubular glands in cellular stroma; after ovulation, progesterone converts the glands to a tortuous, saw-toothed secretory profile with stromal oedema and, by day 24 to 25, predecidual change around spiral arteries. Beneath lies the myometrium, thick interlacing bundles of smooth muscle, and the perimetrium, a serosal or adventitial cover depending on surface.
What you must remember
- Two-layer rule: functionalis sheds, basalis regenerates it — the anatomical basis of menstruation, and why curettage must spare the basalis to avoid Asherman syndrome.
- Blood supply pairing: spiral (coiled) arteries serve the functionalis and constrict before menstruation, producing ischaemic shedding; straight basal arteries serve the basalis and never participate in the shed.
- Proliferative phase (days 5-14): oestrogen-driven; straight glands with mitotically active columnar epithelium, compact stromal cells, and thickness rising from about 1 millimetre toward 3 to 4 millimetres.
- Secretory phase (days 15-28): progesterone-driven; glands become tortuous and saw-toothed with basal glycogen vacuoles then luminal secretion, stroma becomes oedematous, and predecidual change appears around spiral arteries on days 24-25 — the most reliable dating feature on biopsy.
- Implantation window: roughly days 20 to 24 of an idealised cycle, six to ten days after the luteinising-hormone surge — the window that intrauterine insemination and embryo transfer are timed against.
- Myometrium: smooth muscle in interlacing bundles with a central, more compact junctional zone; enlarged by oestrogen-driven hyperplasia in pregnancy, never by cell division alone.
- Cervix contrast: endocervical mucous glands in a branched pattern, no spiral arteries, no cyclical shedding — nabothian follicles form when glands are occluded.
- Pathology anchors: disordered proliferative endometrium in anovulatory cycles; endometrioid carcinoma arising in hyperplasia; adenomyosis — endometrial glands and stroma deep within myometrium; Arias-Stella reaction, a progesterone-induced atypia that must not be misread as cancer.
Dating an endometrial biopsy step by step
A gynaecologist dates a biopsy against the theoretical ovulation day. Start low-power: thin endometrium with straight, test-tube glands and dark, crowded stroma means proliferative — oestrogen is writing the script, and the surface epithelium shows mitoses. Once glands fold, the secretory phase has begun: subnuclear glycogen vacuoles at day 17 align like a picket fence, luminal secretion peaks near day 20, stromal oedema gives a pale, waterlogged look around day 22, and the appearance of predecidual cuffs around spiral arterioles at days 24 to 25 announces that the window for implantation is closing.
If pregnancy does not rescue the corpus luteum, progesterone withdrawal dooms the functionalis. Spiral arteries constrict, the superficial tissue becomes ischaemic and infiltrated by neutrophils, and the layer detaches in the classical mixture of blood, glandular fragments and stroma — menstruation is shedding of the functionalis with basalis preserved, which is why the postmenstrual endometrium is never denuded to the muscle. Read against symptoms, the same biopsy explains abnormal uterine bleeding: an anovulatory adolescent or perimenopausal woman shows disordered proliferative endometrium that outgrows its blood supply and sheds erratically, while a postmenopausal woman on unopposed oestrogen shows hyperplasia, the stepping-stone the pathologist must grade.
How the exam frames endometrium
Two framing devices dominate. First, the artery question: examiners ask which vessel is responsible for menstrual ischaemia and which for regeneration, expecting spiral versus straight basal, and then push toward why functionalis alone sheds — because spiral arteries are uniquely hormone-sensitive and degenerate cyclically. Second, the identification question in practicals: a slide with saw-toothed glands secreting into lumina is secretory endometrium, and candidates must volunteer predecidual change as the day-24 marker to score full marks. The Indian viva favourite is Arias-Stella: glands with hyperchromatic, enlarged nuclei in a gestational or trophoblastic-disease setting, a physiological exaggeration that has been misdiagnosed as adenocarcinoma — naming it demonstrates that the candidate can read function into morphology, exactly what professors reward.
Frequently asked questions
Which endometrial layer is shed during menstruation?
The stratum functionalis, rendered ischaemic by constriction of spiral arteries; the stratum basalis remains to regenerate the surface.
Which histological feature best dates the secretory phase to day 24?
Predecidual change with eosinophilic stromal cells cuffing the spiral arterioles, often with early leucocytic infiltrate.
How do spiral and basal arteries differ functionally?
Spiral arteries supply the functionalis, are sensitive to ovarian hormones and constrict before shedding; straight basal arteries supply the basalis and persist through the cycle.
What is adenomyosis?
Ectopic endometrial glands and stroma embedded at least 2.5 millimetres deep in the myometrium, producing a boggy, enlarged, painful uterus in parous women.
Why does unopposed oestrogen endanger the endometrium?
It drives persistent proliferation without secretory conversion, causing hyperplasia — from simple through atypical — that can progress to endometrioid carcinoma; progesterone opposes this sequence.