DEVELOPMENT OF MALE & FEMALE GENITAL SYSTEM

By

Dr Samina Anjum

DEVELOPMENT OF GONADS

Sex of the embryo is determined genetically at the time of fertilization.

Type of gonads present then determines the type of sexual differentiation that occurs in the genital ducts and external genitalia.

Gonads do not acquire male or female morphological characteristics until the 7th week of development.

Gonadal / Genital ridge

The gonads (testes and ovaries) are derived from three sources : 1.Mesothelial lining the posterior abdominal wall. 2. Condensation of underlying mesenchyme (embryonic connective tissue) 3. Primordial germ cells

Migration of primordial germ cells into developing gonad

.

Primordial germ cells

Arrive at the beginning of 5th week

Invade the genital ridges in the 6th week.

Inductive influence

Indifferent Gonads

• Finger like primitive sex cords appear, grow into underlying mesenchyme, but remained connected to surface epithelium.

Consist of: • External cortex• Internal medulla.

Development of the Testis

SRY gene & TDF Primitive sex cords proliferate, penetrate deep into Medulla to form the testis / Medullary cordsTowards the hilum, the cords break up into tubules of rete testis. The gonadal cords –looses connection with the surface epithelium when thick fibrous capsule develops, tunica albuginea.

• 4th month testis cords become horse shoe shaped and connect with rete testis.

• Spermatogonia -primordial germ cells

• Sertoli cells- the surface epithelium.

• Interstitial cells of Leydig- mesenchyme

• -Testosterone By 8th week

Cont….• Testis cords remain

solid till puberty.• Acquire lumen

forming seminiferrous tubules.

• Once canalized join rete testis which enter ductuli efferentes ---mesonephric duct

Derivatives

The testis cords develop into:• the seminiferous tubules• rete testis.

Mesenchyme between the seminiferous tubules provide

• the interstitial cells of Leydig.

DEVELOPMENT OF OVARY

DEVELOPMENT OF OVARYDegeneration of Primitive/ medullary sex cords

Formation of cortical cords, dissociate into irregular cell clusters which occupy the medullary part of the ovary.

Later, they disappear & replaced by a vascular stroma that forms the ovarian medulla.

7th week, surface epithelium proliferate

Formation of second generation of cords, cortical cords, which remain close to the surface.

4th month, cords split into isolated cell clusters, which surrounds PGCs.

Formation of oogonia & the follicular cells.

Development of ovaries in absence of TDF

DEVELOPMENT OF GENITAL DUCTS

INDIFFERENT STAGE

Initially; both male & female embryos have two pairs of genital ducts: Mesonephric (wolffian)

ducts Paramesonephric

(müllerian) ducts

Paramesonephric ducts arise as a longitudinal invagination of the epithelium on the anterolateral surface of the urogenital ridge.

Cranially, the ducts open into the abdominal cavity with a funnel-like structure.

Caudally, it first runs lateral to the mesonephric duct, then crosses it ventrally to grow caudomedially.

Close contact with the duct of opposite side.

Separated by a septum, later forms the uterine canal.

The caudal tip of the combined duct projects into the posterior wall of the urogenital sinus, the paramesonephric or müllerian tubercle.

Mesonephric ducts open on each side of urogenital sinus

Development of Male Genital Ducts

Ejaculatory duct

At 4th month

After descent of testis

GENITAL DUCTS IN THE FEMALES

After descent of ovaryEnd of 2nd month

When the 2nd part moves mediocaudally, the urogenital ridges come to lie in the transverse plane creating a horizontal fold the broad ligament of the uterus.

DERIVATIVES

Fused paramesonephric ducts give rise to:• Body of uterus• Cervix• Upper part of vagina

Surrounded by: • Mesenchyme ---- Myometrium• Peritoneum ---- Parametrium

DEVELOPMENT OF VAGINA

Shortly after the solid tip of the paramesonephric duct reaches the urogenital sinus, two solid evaginations grow out from the pelvic part of the sinus.

These sinovaginal bulbs proliferate to form a solid vaginal plate.

By the 5th month, the vaginal outgrowth is entirely canalized.

The wing-like expansions of the vagina around the end of the uterus, the vaginal fornices, are of paramesonephric origin.

UTERINE CANAL

UPPER PORTION

UROGENITAL SINUS

LOWER PORTION

Vagina has dual origin

REMANENTS OF MESONEPHRIC DUCT

• Cranial excretory tubules--- epoophoron

• Cuadal excretory tubules--- paroophoron

• Persistent portion of mesonephric duct in uterus or vagina--- Gartner’s cyst

Scrotum, prostate

UTERINE & VAGINAL DEFECTS

a: NORMAL b: UTERUS BICORNIS c: UTERUS DIDELPHYS WITH DOUBLE VAGINA

DEVELOPMENT OF GLANDS IN MALE GENITAL SYSTEM

Endodermal outgrowths from prostatic urethra

Smooth m and stroma derived from surrounding mesenchyme

Prostatic utricle is a sac like structure that opens into prostatic urethra, is homologous to vagina

The lining of Prostatic utricle is derived from epithelium of urogenital sinus.

DEVELOPMENT OF PROSTATE GLAND

DEVELOPMENT OF FEMALE GENITAL GLANDS

(Outgrowths of urogenital sinus)

Development of External Genitalia

Undifferentiated External Genitalia

(3rd to 6th Week)

Male External Genitalia

Female External Genitalia

External GenitaliaIndifferent stage

Development of Male External Geniatlia

1.The indifferent external genitalia are masculinized by the testosterone. 2. The rapid elongation of genital tubercle into phallus. 3. The phallus pulls the urethral folds forward so that they form the lateral walls of urethral groove.4. The urethral groove extends along the caudal aspect of the elongated phallus but does not reach the most distal part, the glans. The groove is lined by endodermal epithelium and forms the urethral plate.

Development of Male External Geniatlia

5. At the end of 3rd month, the two urethral folds close over the uretheral plate, forming the penile urethra. 6. The most distal portion of urethra is formed during the 4th month, when ectodermal cells from tip of glans penetrate inward and form a short epithelial cord. This cord later forms lumen thus forming external urethtral meatus. 7. The labioscrotal swellings fuse to form the scrotum.8. The line of fusion form the scrotal septum.

EXTERNAL GENITALIA IN FEMALES

Estrogens stimulate the development of external genitalia in females.

• Genital tubercle ---- Clitoris• Urethral folds do not fuse ---- labia minora• Genital swellings enlarge ---- labia majora• Urogenital groove is open ---- vestibule

DESCENT OF TESTIS• Towards the end of 2nd month urogenital mesentery attaches the

testis and mesonephros to the posterior abdominal wall. Thus testis begin as retroperitoneal structures in the posterior abdominal wall

• With degeneration of Mesonephros the attachment serves as mesentery for the gonads.

• Caudally urogenital mesentery becomes ligamentous and forms caudal genital ligament.

• Also extends from the caudal pole of testis is a mesenchymal condensation, the gubernaculum.

Caudal genital ligament and

Two parts of gubernaculum can be seen:• Intraabdominal portion: grows prior to descent of testis and

terminates in inguinal region• Extraabdominal portion: grows as testis begins to descend from

inguinal region towards the scrotal swelling. When testis pass through inguinal canal this part contacts the scrotal floor

• As the gubernaculum "pulls" the testes into the pelvis and developing inguinal canal, it is preceded by the processus vaginalis, evagination derived from the peritoneum which lies anterior to the testes. Once testis are in scrotum the gubernaculum persist as scrotal ligament.

Formation of inguinal canal• The processus vaginalis accompanied by muscular and facial

layers of anterior abdominal wall evaginates into scrotal swellings forming inguinal canal.

• Testis are then covered by a reflected fold of processus vaginalis having parietal and visceral layers. The narrow canal connecting the lumen of the vaginal process with the peritoneal cavity is obliterated at birth.

DESCENT OF TESTIS

Congenital Anomalies

INGUINAL HERNIAS & HYDROCELE

Hypospadias

Hypospadias most common abnormality (1 in 300) from a failure of male urogenital folds to fuse in various regions and resulting in a proximally displaced urethral meatus. External urethral orifice is on ventral surface of glans or body.

EPISPADIAS

1/30000 male infants

Urethra opens on dorsal surface

Associated with exostrophy of bladder.

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