DEVELOPMENT OF GONADS AND DUCTULAR SYSTEM IN MALE AND FEMALE

Dr Rania Gabr

OBJECTIVES For the male and female gonads, the

student should be able to: 1. Describe their development. 2. Discuss their congenital anomalies For the male and female genital duct

system: 3. Describe their development. 4. Discuss their congenital anomalies

Genital System

The gonads (testes and ovaries) are derived from three sources : - 1-Mesothelium (mesodermal

epithelium) lining the posterior abdominal wall

- 2-Underlying mesenchyme (embryonic connective tissue)

- 3-Primordial germ cells

- The greater part of the genital system arises from the mesoderm of the intermediate cell mass.

- It develops in conjunction with the urinary system.

- Germ cells migrate from the yolk sac to the intermediate mesoderm medial to the developing mesonephros.

- The Genital ridge forms at the 10th thoracic level medial and ventral to the mesonephros.

- Fingerlike epithelial cords-the gonadal cords-soon grow into the underlying mesenchyme

- Early development of males and females are similar (Indifferent phase).

Stages of development of gonads:

1- Indifferent gonads:

The initial stages of gonadal development occur during the fifth week

Before the 7th week as we can’t differentiate between ovary and testis.

2- Differentiation:

After the 7th week as gonads becomes differentiated into testis or ovary.

DEVELOPMENT OF THE TESTIS

Under the influence of sex determining factor (SDF), the primitive sex cords proliferate & anastomose with one another forming the “testis cords” which are formed of the epithelial cells of the coelomic cavity & the germ cells.

Testis cords separate from the epithelial lining of the coelomic cavity & become surrounded by a fibrous layer which develops to give tunica albuginea of the testis.

Testis cords bend to form horseshoe seminiferous tubules.

Their ends remain straight forming the straight tubules & become connected to rete testis.

The seminiferous tubules start to function, acquire a lumen & produce sperms from the germ cells after puberty.

Epithelial cells in the seminiferous tubules form Sertoli cells.

By eighth week, mesenchyme surrounding testis cords gives rise to interstitial cells (of Leydig) secreting testosterone.

In Medulla

Germ cells

Mesothelial cells

Descent of the testis:

The testis is connected to the scrotal swelling by a fibrous cord (caudal genital lgament) called the “gubernaculum testis”.

This fibromuscular band is attatched also to the peritoneum in front of the testis.The continuous shortening of the gubernaculum pulls the testis from the upper part of the abdomen to the scrotum with a peritoneal sac known as processus vaginalis.

The testis is found in:

- 7th week : Post. Abdominal wall- The iliac fossa on the 3rd month

of IU life.- The inguinal canal on the 7th

month (28 wks) of IU life- The superficial inguinal ring on

the 8th month of IU life.- The scrotum on the 9th month of

IU life.

With the descent of the testis, the neck of the sac is approximated & obliterated so that a small separate sac of peritoneum incompletely surrounds the testis forming tunica vaginalis testis.

Congenital anomalies of the testis:

1) Undescended testis (cryptorchidism).2) Maldescended testis(ectopic testis): The

testis may be found at the dorsum of penis, the anterior abdominal wall, front of thigh or perineum.

3) Congenital inguinal hernia.4) Congenital hydrocele.

CONGENITAL INGUINAL HERNIA

Definition: Herniation of a loop of intestine through a non-obliterated processus vaginalis.

A: incomplete B: complete (in scrotum)

Cause: The processus vaginalis does not obliterate & remains in open communication with the peritoneal cavity.

HYDROCELE OF SPERMATIC CORDAccumulation of fluid in spermatic

cord due to a non-obliterated portion of stalk of processus vaginalis

HYDROCELE OF TESTISAccumulation of fluid in tunica vaginalis

(in scrotum) due to non-obliteration of the whole stalk of Processus vaginalis

DEVELOPMENT OF THE OVARY- The primitive sex cords degenerate & become

replaced by vascular fibrous tissue which forms the permanent medulla.

- The epithelium of the coelomic cavity proliferates & become thicker. It forms the second generation of cords known as cortical cords.

- The cortical cords split into separate follicular cell clusters surrounding germ cells & form together primordial follicles.

The primordial germ cells are incorporated in the cortical cords.

At the 16 weeks the cortical cords break up into isolated cell clusters, primordial follicles.

The primordial follicles contain Oogonia; derived from the Primitive Germ Cells, and surrounded by a single layer of flattened Follicular Cells derived from the surface epithelium .

Active Mitosis of Oogonia produce thousands of primordial follicles

(No New Oogonia Are Formed After Birth).

Many oogonia degenerate . Two milion oogonia enlarge to

become Primary Oocytes Before Birth .

Primary Oocytes

DEVELOPMENT OF THE DUCTS OF THE

GONADS2 ducts are formed in

male & female embryos: 1- Mesonephric (Wolffian ) 2-Paramesonephric

(Mullerian) duct.

In male embryo:

- Mullerian duct degenerates (except the uppermost part which forms appendix testis & lowermost part which forms prostatic utricle).

- Wolffian duct= Mesonephric duct:

- Its upper part becomes markedly convoluted forming the epididymis.

- The middle part forms the vas deferens.

- The lower part forms a small pouch which forms the seminal vesicle.

- The terminal part forms the ejaculatory duct.

- (The upper most part of the duct forms appendix epididymis).

- Mesonephric tubules opposite the developing testis forms efferent ducts which become connected to rete testis.

DEVELOPMENT OF MALE GENITAL DUCTS

Leydig’s cells Sertoli cells

Testosterone (8th week) Müllerian inhibiting substance(Anti- Müllerian hormone) (7th week)

1) Masculine differentiation ofmesonephric duct: epididymis,vas deferens, seminal glands, ejaculatory duct.

2) Masculine differentiation ofexternal genitalia

Suppression of developmentof paramesonephric

(Müllerian) duct

In female embryo:

- Wolffian duct (mesonephric duct) degenerates (except the most caudal part which remains connected to the uterus or vagina, epoophoron, paroophoron & if enlarged it forms (Gartner’s cyst).

- Mullerian duct:- Its upper vertical1/3 (lateral to wolffian

duct) & middle 1/3 (horizontal & in front of Wolffian duct) form the uterine tube.

- The lower 1/3 of both ducts fuse together & forms a single tube (uterovaginal canal) which forms the uterus & the cervix and upper 3/5 of the vagina.

- As the paramesonephric ducts descend through the pelvis, they pull toward the midline a transverse fold of coelomic epithelium on each side which form the broad ligament.

DEVELOPMENT OF LOWER PORTION OF VAGINA

The contact of the uterovaginal primordium with the urogenital sinus induces formation of SinoVaginal Bulbs.

The bulbs proliferate and fuse to form a solid Vaginal Plate.

The central cells of the vaginal plate break down to form the lumen of the vagina.

The lumen of the vagina remains separated from that of the urogenital sinus by a thin tissue plate, the hymen .

Congenital malformations:1) Double uterus:- Uterus didelphys with double vagina.- Bicornuate uterus.- Arcuate uterus- Uterus bicornis unicollis. 2) Unicornuate uterus. 6) Septate uterus3) Atresia of cervix. 7) Bipartite uterus4) Atresia of vagina5) Imperforate hymen.

Development of female genital duct (no A & AMH)1) Paramesonephric duct → uterine tube; Uterine canal → uterus, upper 1/3 of vagina.

2) Sinus tubercle → vaginal plate → canalized → lower 2/3 of vagina.

3) Mesonephric ducts → degenerate.

Indifferent Male Female

Gonad Testis Ovary

Paramesonephric duct(Mullerian duct)

Appendix testis Fallopian tubes

Paramesonephric duct Prostatic utricle Uterus, upper vagina

Mesonephric tubules Efferent ducts, Paradidymis

Epoophoron, Paroöphoron

Mesonephric duct(Wolffian duct) Rete testis Rete ovarii

Mesonephric duct Epididymis Gartner's duct

Mesonephric duct Vas deferens

Mesonephric duct Seminal vesicle

Urogenital sinus Prostate Skene's glands

Urogenital sinus Bladder, urethra Bladder, urethra, lower vagina

Urogenital sinus Cowper's or Bulbourethral gland Bartholin's gland

Labioscrotal folds Scrotum Labia majora

Urogenital folds Spongy urethra Labia minora

Genital tubercle Penis Clitoris

Genital tubercle Bulb of penis Vestibular bulbs

Genital tubercle Glans penis Clitoral glans

Genital tubercle Crus of penis Clitoral crura

Prepuce Foreskin Clitoral hood

Peritoneum Processus vaginalis Canal of Nuck

Gubernaculum Gubernaculum testis

Round ligament of uterus

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