Female genital tract development
Development of the ovary, uterus, tubes, cervix and vagina: Müllerian and Wolffian ducts
Every embryo starts with the same indifferent gonad, two pairs of genital ducts and one set of external genital swellings. Whether these become male or female depends on two testicular hormones, AMH and testosterone; without them the female pattern forms by default. CPSP asks which duct gives which organ, what each remnant is, and why the ovary drains to the para-aortic nodes.
Primordial germ cells and the indifferent gonad
- Primordial germ cells arise from the epiblast in week 2, are first seen in the wall of the yolk sac near the allantois, then migrate by amoeboid movement along the dorsal mesentery of the hindgut to reach the genital ridges by week 6. They do not travel in the blood.
- The genital (gonadal) ridge forms on the posterior abdominal wall, medial to the mesonephros, at upper lumbar level from coelomic epithelium and underlying mesenchyme. The adrenal cortex comes from the same coelomic mesoderm next to it, which explains adrenal rests found near the ovary, in the broad ligament or in the testis (they enlarge under high ACTH in CAH).
- If germ cells fail to arrive, a streak gonad results. Germ cell tumours (teratoma) can contain all three layers.
- Until week 7 the gonad looks the same in both sexes.
Sex determination
- SRY on the short arm of Y switches on SOX9, and the supporting cells become Sertoli cells. An SRY fragment translocated onto an X gives a 46,XX male. WT1 (11p13) is needed for both gonad and kidney.
- Testis: medullary (testis) cords and an early thick tunica albuginea, the first histological sign of a testis.
- Ovary: medullary cords regress; cortical cords surround each oogonium. Cortical cord cells become granulosa cells; theca cells come from ovarian stromal mesenchyme.
- Oocyte numbers: peak about 7 million at 20 weeks, 1–2 million at birth, about 400,000 at puberty; only 400–500 are ovulated. Fetal primary oocytes arrest in prophase of meiosis I (diplotene); the ovulated oocyte arrests in metaphase II until fertilisation.
Two hormones decide the ducts
| Hormone | Source in male | Effect | If absent |
|---|---|---|---|
| AMH (Müllerian inhibiting substance) | Sertoli cells | Active regression of paramesonephric ducts | Uterus, tubes, upper vagina persist |
| Testosterone | Leydig cells | Keeps mesonephric ducts | Mesonephric ducts regress passively |
| DHT (via 5-alpha reductase) | Converted in target tissue | Masculinises external genitalia, prostate | External genitalia stay female |
- The female pathway needs no gonadal hormone in utero, so a girl with streak ovaries (Turner) has normal female genitalia at birth.
- In the adult woman, AMH is made by granulosa cells of small growing follicles and is used as a marker of ovarian reserve. It appears too late in female fetal life to affect the ducts.
Paramesonephric (Müllerian) ducts
- Form in week 6 as a groove of coelomic epithelium lateral to the mesonephric duct; they need the mesonephric duct as a guide.
- Cranial open end: becomes the abdominal ostium of the tube, which is why the female genital tract opens into the peritoneal cavity (dye spill at laparoscopy, ascending infection).
- Cranial unfused vertical parts: the uterine tubes.
- Caudal fused parts (uterovaginal primordium): uterus, cervix and upper vagina including the fornices. Fusion lifts a transverse pelvic fold, the broad ligament, with the vesicouterine pouch in front and the pouch of Douglas behind.
- The ducts give only the epithelium (endometrium, endocervix). Myometrium and endometrial stroma come from surrounding mesenchyme, so fibroids are mesenchymal in origin.
- Peritoneum and Müllerian epithelium share a coelomic origin; this underlies the coelomic metaplasia theory of endometriosis.
Vagina and external genitalia
- The fused duct tips meet the urogenital sinus at the sinus (Müllerian) tubercle; the male homologue is the seminal colliculus.
- Sinovaginal bulbs grow from the sinus and form a solid vaginal plate, which canalises by the 5th month. The lower vagina therefore comes from the urogenital sinus; the hymen marks the junction with the sinus.
- Genital tubercle: clitoris (male: penis). Urogenital folds: labia minora (male: penile urethra; failure gives hypospadias). Labioscrotal swellings: labia majora (male: scrotum). Urogenital sinus: vestibule.
- Bartholin gland = bulbourethral (Cowper) gland. Skene (paraurethral) gland = prostate.
Remnants and gonadal descent
| Remnant | Origin | Site |
|---|---|---|
| Epoophoron | Cranial mesonephric tubules | Mesosalpinx |
| Paroophoron | Caudal mesonephric tubules | Broad ligament near uterus |
| Gartner duct cyst | Mesonephric duct | Anterolateral vaginal wall |
| Appendix vesiculosa (hydatid) | Cranial end of mesonephric duct | Near fimbriae |
| Male appendix testis, prostatic utricle | Paramesonephric duct | Testis, prostatic urethra |
- Male mesonephric derivatives: epididymis, ductus deferens, seminal vesicle, ejaculatory duct; the trigone is mesonephric in both sexes.
- The gubernaculum in the female becomes the ovarian ligament and the round ligament (through the inguinal canal to the labium majus). The suspensory (infundibulopelvic) ligament is not gubernacular.
- The ovary forms at upper lumbar level and descends, trailing its vessels: ovarian artery from the aorta at L2, right vein to the IVC, left vein to the left renal vein, lymph to para-aortic nodes. Ovarian cancer can involve para-aortic nodes with clear pelvic nodes.
Remember Remember the rule of defaults: no AMH means a uterus, no testosterone means no Wolffian ducts, no DHT means female external genitalia.
Exam trap Wolffian ducts regress for lack of testosterone, not because AMH destroys them; AMH acts only on the Müllerian ducts.
Exam trap A cyst in the anterolateral upper vaginal wall is a Gartner duct cyst; a Bartholin cyst sits posterolaterally at the introitus.
Test yourself on this topic
5 of the 35 questions in our bank on this topic. Choose an answer to see why every option is right or wrong.
A 28-year-old woman has a fluctuant swelling in the posterior part of the left labium majus from a blocked greater vestibular (Bartholin) gland. What is the male homologue of this gland?
Answer: Bulbourethral gland
The greater vestibular glands of the female and the bulbourethral glands of the male both arise as outgrowths of the urogenital sinus in the lower urogenital region. Both lie in relation to the perineal membrane and secrete mucus during sexual arousal. The prostate is homologous with the paraurethral glands. The seminal vesicle and ejaculatory duct come from the mesonephric duct.
Bartholin gland
- Posterior labium majus
- Homologue: bulbourethral gland
- Origin: urogenital sinus
- Mucus for lubrication
Remember Bartholin and Cowper are a pair.
Exam trap Skene, not Bartholin, matches the prostate.
Why the other options are wrong
- Prostate gland Homologue of Skene glands.
- Seminal vesicle Mesonephric derivative.
- Ejaculatory duct Mesonephric derivative.
- Urethral glands of Littre Small urethral mucous glands; not the paired homologue.
During a vaginal hysterectomy, the surgeon incises the vaginal wall circumferentially in the anterior and posterior fornices around the cervix. From which embryonic structure is the wall of the fornices derived?
Answer: Fused caudal paramesonephric ducts
The vagina has a dual origin. The solid tip of the fused paramesonephric ducts (uterovaginal canal) forms the cervix and the region around it, including the fornices, while the vaginal plate from the sinovaginal bulbs forms the rest of the vagina. The fornices are therefore of paramesonephric origin. The mesonephric ducts regress in females, leaving only Gartner duct remnants in the lateral vaginal wall.
Vaginal fornices
- Fornices are paramesonephric
- Around the cervix
- Rest of vagina from vaginal plate
- Hymen marks the urogenital sinus junction
Remember Fornices belong to the ducts, like the cervix.
Exam trap The posterior fornix is upper vagina, so it shares the Müllerian origin of the cervix.
Why the other options are wrong
- Sinovaginal bulbs Form the vaginal plate and lower vagina.
- Pelvic part of the urogenital sinus Forms the female urethra.
- Caudal mesonephric ducts Leave only Gartner duct remnants.
- Phallic part of the urogenital sinus Forms the vestibule.
A 46,XX infant born with complete absence of both gonads has a normal uterus, tubes, vagina and female external genitalia. Which of the following best explains why her mesonephric (Wolffian) ducts regressed?
Answer: No testosterone from fetal Leydig cells
The mesonephric ducts are kept alive only by local testosterone from fetal Leydig cells; without it they regress. This baby has no gonads, so she has no testosterone and her mesonephric ducts disappear, while the paramesonephric ducts persist because there is no AMH. Ovarian oestrogen is not needed for female duct or genital development, which is the default. AMH acts on the paramesonephric, not the mesonephric, ducts.
Which hormone keeps which duct
- Testosterone keeps mesonephric ducts
- AMH removes paramesonephric ducts
- No gonad: female ducts and genitalia
- Female path needs no hormone
Remember No gonads, female pattern.
Exam trap Wolffian regression is passive loss of testosterone, not active destruction by AMH.
Why the other options are wrong
- Action of AMH on the mesonephric ducts AMH regresses the paramesonephric ducts, and there is none here.
- Oestrogen from the fetal ovaries She has no ovaries, and oestrogen is not required anyway.
- Absence of SRY in the duct epithelium The ducts respond to hormones, not to their own SRY status.
- Placental hCG acting on the ducts hCG drives Leydig cells but there are none here.
A 38-year-old woman asks why her egg supply falls with age. You explain that the total number of germ cells in the ovary is greatest during fetal life and declines from then on. When is this peak reached?
Answer: Around 20 weeks of gestation
Oogonia multiply rapidly by mitosis, and the total germ cell count peaks at about 7 million around the fifth month (about 20 weeks) of fetal life. After this, many oogonia and primary oocytes degenerate by atresia, leaving around 1–2 million at birth and about 400,000 at puberty. No new oocytes are formed after birth. Only about 400–500 will ever ovulate.
Germ cell numbers
- Peak: 7 million at 20 weeks
- Birth: 1–2 million
- Puberty: about 400,000
- Ovulated: only 400–500
Remember The ovary is richest before birth.
Exam trap The peak is in mid-fetal life, not at birth.
Why the other options are wrong
- At about 8 weeks of gestation Germ cells have only just reached the gonad.
- At the time of birth About 1–2 million remain by birth.
- At menarche Only about 400,000 remain.
- At about 12 weeks of gestation Numbers are still rising.
A 45-year-old woman with ovarian cancer has enlarged lymph nodes beside the aorta at the level of the renal veins, but no pelvic node disease. Which embryological fact best explains this pattern of spread?
Answer: The ovary develops on the posterior abdominal wall
The gonad forms in the genital ridge on the posterior abdominal wall, at about the upper lumbar level, and later moves down into the pelvis. Its blood vessels and lymphatics are drawn down with it, so the ovarian arteries arise from the aorta near L2 and its lymph returns to para-aortic nodes at that level. Lymph from the uterine cornu can travel along the round ligament to inguinal nodes, but that is not the main ovarian route.
Why the ovary drains high
- Gonad forms at upper lumbar level
- Descends, trailing its vessels
- Ovarian artery from aorta at L2
- Lymph to para-aortic nodes
Remember Gonads drain to where they were born.
Exam trap Pelvic nodes may be clear even when ovarian cancer has reached the para-aortic chain.
Why the other options are wrong
- The ovary arises from the paramesonephric duct The ovary comes from the genital ridge, not the duct.
- Ovarian lymph follows the round ligament That route serves the uterine cornu, toward inguinal nodes.
- The ovary is a derivative of the hindgut The hindgut does not form the ovary.
- Ovarian vessels arise from the internal iliac Ovarian arteries arise from the aorta.
Where this sits in the CPSP syllabus
- Obstetrics & Gynaecology, Paper 2: Embryology, Development of the ovary, uterus, cervix, tubes and vagina; Mullerian and Wolffian ducts