Histology · Reproductive system
Uterus and the endometrial cycle !
- Organ
The lining of the uterus grows, gets ready and is shed each month, following the hormones of the ovary.
Updated 2026-11-01
See it in 3D: Endometrium · Body of uterus · Myometrium
What it is
The uterine wall has three layers: endometrium (mucosa), myometrium (smooth muscle) and perimetrium (serosa). The endometrium has a functional layer, which changes and is lost at menstruation, and a basal layer, which stays and regenerates it. Estradiol makes the endometrium grow and progesterone makes it secretory and ready for implantation. Dating the endometrium by its glands and stroma is a classic histology question.
Structure
- Endometrium: simple columnar epithelium with ciliated and secretory cells, tubular glands and a very cellular stroma.
- Myometrium: thick interlacing bundles of smooth muscle with vessels; it grows a lot in pregnancy by hypertrophy and hyperplasia.
- In pregnancy the stroma becomes decidua: large, polygonal, pale cells.
Function
- Prepare a bed for embryo implantation each cycle.
- Form the maternal part of the placenta (decidua basalis).
- Expel the fetus at birth by contraction of the myometrium.
Endometrial phases (reference 28-day cycle)
| Phase | Hormone in charge | What you see |
|---|---|---|
| Menstrual (days 1 to 4) | Fall in progesterone and estradiol | Collapsed stroma, blood and shedding of the functional layer |
| Proliferative (days 5 to 14) | Estradiol from the follicle | Straight glands with mitoses; dense stroma; the endometrium thickens |
| Early secretory (days 15 to 19) | Progesterone from the corpus luteum | Glycogen vacuoles below the nucleus of gland cells |
| Late secretory (days 20 to 28) | Progesterone | Tortuous glands with secretion in the lumen, edematous stroma, predecidual change around spiral arteries |
Clinical notes
- Endometriosis: endometrial glands and stroma outside the uterus; pelvic pain and infertility.
- Adenomyosis: endometrium inside the myometrium; a large, painful uterus.
- Leiomyomas (fibroids): benign smooth muscle tumours, the most common tumours of the uterus.
- Postmenopausal bleeding: the endometrium must be studied because of the risk of carcinoma.
Test yourself
Think of the answer, then tap the question to see it.
Which endometrial layer is lost at menstruation, and which regenerates it?
The functional layer is lost; the basal layer stays and regenerates it.
Which finding marks the start of the secretory phase?
Glycogen vacuoles below the nucleus of the gland cells, soon after ovulation.
Which hormone drives the proliferative phase?
Estradiol from the growing follicles.
Why does estrogen unopposed by progesterone raise the risk of endometrial cancer?
It drives continuous gland proliferation, which can lead to hyperplasia and then to endometrioid carcinoma.
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
Related
- Ovary: follicles, ovulation and corpus luteum
- Cervix and vagina: the transformation zone
- Placenta
- Smooth muscle
Related conditions
Educational content on normal microscopic structure and its clinical relevance; no substitute for studying slides or for a health professional's advice.
Sources: 27.2 Anatomy and Physiology of the Ovarian Reproductive System (OpenStax, Rice University, 2022); Genital Tract (National Cancer Institute, SEER Training Modules, 2026).
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Representative model, for educational purposes only.