Histology of the female and male reproductive organs and genitourinary tract

Overview

Histology questions in PGET usually ask which epithelium lines an organ, which cell makes a hormone, or which layer changes in the cycle or in disease. Learn the master table first, then the special points for each organ.

Master table of epithelia

Vulva and vagina

• Vagina wall: mucosa (non-keratinised stratified squamous over a lamina propria rich in elastic fibres and thin veins), smooth muscle (mainly longitudinal outer, circular inner) and adventitia.
• There are no glands; moisture comes from cervical mucus and transudate.
• Oestrogen thickens the epithelium and fills the cells with glycogen. Döderlein's lactobacilli break glycogen down to lactic acid, keeping the pH about 4.5 and protecting against pathogens.
• Before puberty and after menopause, low oestrogen gives a thin, atrophic epithelium and a higher pH (risk of atrophic vaginitis).
• Bartholin's glands: mucus-secreting acini with ducts that open into the vestibule.

Cervix

• Ectocervix: non-keratinised stratified squamous.
• Endocervix: tall columnar mucus-secreting cells lining branching clefts (crypts), often called glands. The mucus is alkaline and changes with the cycle (thin and stretchy at ovulation, thick under progesterone).
• Stroma: mostly dense collagen with little smooth muscle in the lower cervix; this collagen softens and remodels before labour.

Squamocolumnar junction and transformation zone

• The original squamocolumnar junction (SCJ) is where the two epithelia met at birth.
• At puberty, in pregnancy and on the combined pill, the cervix everts and endocervical columnar epithelium is exposed on the ectocervix (ectropion). Vaginal acid makes it change to squamous epithelium (squamous metaplasia).
• The area between the original and the new SCJ is the transformation zone. Its immature metaplastic cells are the target of HPV and the site where CIN and cervical cancer start.
• Crypt openings blocked by metaplastic squamous cells form mucus-filled Nabothian follicles (cysts): harmless.

Uterus

Endometrium

• Simple columnar epithelium (with some ciliated cells) dipping down as tubular glands into a cellular stroma.
• Two layers:
  • Stratum functionalis (upper): grows each cycle and is shed at menstruation. Supplied by spiral arteries.
  • Stratum basalis (deep): not shed; contains the stem cells that regenerate the functionalis. Supplied by straight arteries.

Myometrium and serosa

• Myometrium: interlacing smooth muscle bundles with vessels; it enlarges in pregnancy mainly by hypertrophy of fibres. Benign smooth-muscle tumours here are fibroids (leiomyomas).
• Serosa: peritoneum over the body.

Fallopian tube

• Mucosa: branched longitudinal folds (plicae), most complex in the ampulla, lined by:
  • ciliated cells, which beat towards the uterus and move the ovum and embryo;
  • secretory (peg) cells, which make tubal fluid that nourishes gametes.
• No submucosa and no glands; the epithelium sits almost on the muscle.
• Muscle: inner circular, outer longitudinal; peristalsis helps transport.
• Cells change with the cycle (more cilia and secretion near ovulation) but are not shed at menstruation.
• Damage to cilia and folds after infection (for example chlamydia) is why tubal infertility and ectopic pregnancy follow PID.

Ovary

Follicle stages

• Two-cell system: under LH, theca interna makes androgens; under FSH, granulosa cells convert them to oestradiol with aromatase.
• Most follicles die by atresia, leaving atretic follicles.

Urinary tract

• Urothelium (transitional epithelium) lines the renal pelvis, ureter, bladder and upper urethra. Its surface "umbrella" cells flatten when the bladder fills.
• Ureter: star-shaped lumen; muscle has two layers in the upper part and a third (outer longitudinal) layer lower down.
• Bladder: detrusor smooth muscle in three layers.
• Female urethra: about 3.5 cm; transitional epithelium near the bladder becoming stratified squamous at the meatus; a vein-rich submucosa; striated compressor urethrae.
• Long-term irritation (indwelling catheter, stones, schistosomiasis) can turn urothelium into keratinising squamous epithelium (squamous metaplasia), a step towards squamous carcinoma.

Male reproductive organs

Testis

• Covered by a tough tunica albuginea; divided into lobules holding up to about 900 coiled seminiferous tubules (Guyton).
• Seminiferous tubule wall: Sertoli cells resting on the basement membrane, with germ cells between them maturing towards the lumen: spermatogonia → primary spermatocytes → secondary spermatocytes → spermatids → spermatozoa.
• Spermatogenesis starts at puberty and one cycle from spermatogonium to sperm takes about 74 days.

Ducts and glands

Quick revision

• Vagina and ectocervix: non-keratinised stratified squamous; no glands; pH about 4.5.
• Endocervix: mucus-secreting columnar with crypts; transformation zone = cancer site.
• Endometrium: functionalis shed, basalis regenerates; secretory glands are coiled with vacuoles.
• Tube: ciliated + peg cells, plicae, no submucosa.
• Ovary: simple cuboidal surface, tunica albuginea, cortex follicles.
• Theca (LH) → androgens; granulosa (FSH, aromatase) → oestradiol.
• Sertoli: barrier, AMH, inhibin; Leydig: testosterone. Spermatogenesis about 74 days.
• Epididymis and vas: pseudostratified with stereocilia; urinary tract: urothelium.

Written by The House Job from standard references (Gynaecology by Ten Teachers; Guyton and Hall Textbook of Medical Physiology; Snell's Clinical Anatomy).

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