razvoj ovariuma

CHAPTER 1

EMBRYOLOGY OF THEREPRODUCTIVE TRACT

Development of the Ovary 2Development of Uterus and Fallopian Tubes 5Development of External Genitalia 7Development of Male External Genitalia 9

The germ cells, which will eventually inhabitthe gonads, originate from the primitivehind gut. They appear around the 25th day.

By 30 days, the gut, complete with itsmesentery, is formed. The germ cells nowmigrate from the gut to the root of themesentery. Of the original 6 or 7 million,only 1–2 million are present at birth and thisnumber is reduced to 300,000 at puberty.A smaller number of these cells may be afactor that leads to premature menopause.

At the same time, the coelomic epitheliumproliferates and forms thickenings, the genitalridges, together with the underlyingmesenchyme on either side of the mesentericroot, near the developing kidney.

Vitelline duct

Allantois

Hindgut

Mesonephricduct andtubules

MetanephrosPrimordialgerm cells

CloacaTransverse Section of Embryo

Spinal cord

Notochord

Aorta

Mesonephricduct

Meso-nephrosGenital

ridge

GutCoelomicorperitonealcavity

Allantois

Amniotic cavity

Germ cells

Embryo

Yolk sac

DEVELOPMENT OF THE OVARY

EMBRYOLOGY OF THE REPRODUCTIVE TRACT

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At this stage, the primitive gonad(genital ridge) consists of amesoderm (coelomic epitheliumplus mesenchyme) covered by thecoelomic epithelium. The germcells now migrate from the root ofthe mesentery to the genital ridge.

The coelomic epithelium, growinginto the genital ridge, forms theso-called sex cords, which encloseeach germ cell.

Until this time, that is, around the7th week, the gonad is of an indifferenttype, the male being indistinguishablefrom the female.

The germ cells and most of the sexcord cells remain in the superficialpart, which is the future cortex of theovary. The cords then lose contact withthe surface epithelium and form smallgroups of cells, each with its germ cell, aprimitive follicle. Some of the sex cordcells grow into the medulla. Thesetend to regress and formrudimentary tubules, the rete.

As the ovary grows, it projectsincreasingly into the peritoneal(coelomic) cavity, thus forming amesentery.

Mesonephricduct

Mesonephricswelling

Genital ridge

Germcells

Coelomic epithelium

Gut

Mesonephrictubules

Germcells

Coelomic epithelium(primitive germinal epithelium)

Mesenteryof ovary

Degeneratingmesonephrictubules

andduct

Primitive follicles



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Simultaneously, the ovary descends extraperitoneally within the abdominal cavity. Twoligaments develop and these may help to control its descent, guiding it to its final positionand preventing its complete descent through the inguinal ring, in contrast to the testes.The first structure is the suspensory ligament attached to the anterior (cephalic) pole of theovary which connects it with its site of origin, the genital ridge.

Another ligament, or gubernaculum, develops at the posterior or caudal end of the ovary. Atfirst attached to the genital ridge, it later becomes attached to the developing uterus andbecomes the ovarian ligament.

Suprarenalgland

Kidney

Ureter

Bladder

Suspensoryligament

Ovary

Mesonephricduct

Mesonephros

Gut

Gubernaculum



4

When the embryo reaches a size of 10 mm at 35–36 days, a longitudinal groove appears on thedorsal aspect of the coelomic cavity, lateral to the Wolffian (mesonephric) ridge.

Mesonephricduct

Primitivegonad

Gut

Para-mesonephricgroove

becomes

Para-mesonephricduct

Mesonephricduct

Mesonephros

Gonad

Kidney

Mesonephric duct

Ureter

Cloaca

This groove or fold is then sealed off toform a tube, the paramesonephric orMullerian duct. The tube is open at itsupper end, enabling communication withthe future peritoneal cavity. The lower endforms a solid tip (Mullerian tubercle),which develops burrowing properties.

DEVELOPMENT OF UTERUS AND FALLOPIAN TUBES


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The Mullerian ducts from either side grow in a caudal direction, extraperitoneally. They alsobend medially and anteriorly and ultimately fuse in front of the hind gut. The mesonephricduct becomes involved in the walls of the paramesonephric ducts.

Gubernaculum ofovary(ovarian ligament) Ovary

Fallopian oruterine tube

Developinguterus

Mülleriantubercle

Urogenitalsinus

Degeneratingmesonephricduct (becomesGartner’s duct)

Uterus

Ovary

Bladder

Ovariangubernaculum

attached tocornu ofuterus

Part of itcontinuesas theroundligament.

After passingthrough theinguinal canalit ends in thelabium majusof the vulva.

Symphysispubis

Urogenitalsinus

Hymen

At first, there is a septum that separates the lumina of the twoducts. Later the septum disappears and a single cavity isformed, the uterus. The upper parts of both the ducts remainseparate and form the fallopian tubes.

MesonephricPara-

mesonephricductsducts

While this is happening, the ovary is alsoaffected. Its gubernaculum is ultimatelyattached to the Mullerian duct at thecornu of the developing uterus. Thispulls the ovary medially such that itslong axis becomes horizontal.

The lower end of the fused Mullerian ducts,beyond the uterine lumen, remains solid,proliferates and forms a solid cord. This cordwill canalise to form the vagina, whichopens into the urogenital sinus.

At the point of entry into the urogenitalsinus, a part of the Mullerian tuberclepersists and forms the hymen.

DEVELOPMENT OF UTERUS AND FALLOPIAN TUBES


6

At an early stage, the hind gut andthe various urogenital ducts open intoa common cloaca.

A septum (urorectal) grows downbetween the allantois and the hind gutduring the 5th week.

Cloacalmembrane Urorectal

septum

Ureter

Hind gutAllantois

Cloaca

Ureter

Eventually, this septum fuses with the cloacal membrane, dividing the cloaca intotwo compartments – the rectum dorsally and the urogenital sinus ventrally. Atthe same time, the developing uterus grows down and makes contact with theurogenital sinus.

At the end of the 7th week, the urogenital membrane breaks down and the urogenital sinusopens on to the surface.

The developing uterus and vagina push downwards and cause an elongation and narrowing ofthe upper part of the urogenital sinus. This will form the urethra.

Ureter

Genitaltubercle

Urogenitalmembrane

Anal membrane

Uterus

Hind gut

Urogenitalsinus

Rectum

Allantois (or urachus)

Uterine body

Cervix

Vagina

Urogenitalsinus (orvestibule)

Bladder

Developingurethra

Genitaltubercle

DEVELOPMENT OF EXTERNAL GENITALIA


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Meanwhile, on the surface of the embryo, around the urogenital sinus, five swellings appear.At the cephalic end, a midline swelling grows, the genital tubercle, which will become theclitoris. Posterior to the genital tubercle and on either side of the urogenital membrane a foldis formed – urethral folds. Lateral to each of these another swelling appears – the genital orlabial swelling. These swellings approach each other at their posterior ends, fuse and form theposterior commissure. The remaining swellings become the labia minora.

Certain small, but clinically important, glands areformed in and around the urogenital sinus.

In the embryo, the epithelial buds arise from theurethra and also from the epithelium of theurogenital sinus. In the male, these two setsof buds grow together and give rise to the glandsof the prostate. They remain separate in thefemale, with the urethral buds forming the urethralglands and the urogenital buds giving rise to theparaurethral glands of Skene. The ducts of thelatter open into the vestibule, on either side ofthe urethra.

Two other small glands arise by budding from theepithelium of the posterior part of the vestibule, oneon either side of the vaginal opening. These are thegreater vestibular or Bartholin’s glands. Similarsmaller glands also arise in the anterior portion of thevestibule.

Genitaltubercle

Urogenitalmembrane

Analmembrane

Labialswelling

Urethralfold

Labiumminus

Vestibule

Posteriorcommisure

Anus

Clitoris

Labiummajus

Prepuce Clitoris

Urethra

Ducts ofglands ofSkene

Labiumminus

Vestibule

Vagina

Labium majus

Greater vestibular(Bartholin’s) gland ducts

DEVELOPMENT OF EXTERNAL GENITALIA


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As in the female, a mesodermal mass, theurorectal septum, grows downwards andseparates the urogenital sinus from the rectumand anus. The urogenital portion of thecloacal membrane disintegrates and an opengutter is formed through which the urinedrains. This gutter is continuous anteriorlywith the primitive urethral groove on thephallus.

The ectoderm on the under surface of thephallus disappears, exposing the underlyingendodermal plate.

The endodermal plate then becomes hollowedand forms the primary urethral groove.

The hollow endodermal plate is drawn backinto the body of the phallus and, in this process,it forms a tube. The ectodermal surface is thenrestored.

Simultaneously, the urethral folds areapproximated and ultimately fuse.

The testes descend into the labio-scrotalswellings which then become distended andmove medially to form the scrotum.

Urogenitalsinus

Glans penis

Primitiveurethralgroove

Anal pit

Scrotalswelling

Endodermal plate

Ectoderm Ectoderm

Penileurethra

Genitalraphe

Primary urthral groove

Urethral fold

Phallus

Scrotum

Glans penis

Primitiveurogenitalorifice

Genitalraphe

DEVELOPMENT OF MALE EXTERNAL GENITALIA


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