Development of the Genital System PDF

Development of Genital System Basma Said Abdel-Tawab Lecturer of Human Anatomy and Embryology  Objectives Development of gonads 2 stages: Indifferent stage Development of genital ducts...

Development of Genital System Basma Said Abdel-Tawab Lecturer of Human Anatomy and Embryology  Objectives Development of gonads 2 stages: Indifferent stage Development of genital ducts Differentiation stage Development of external genitalia  Development of gonads Indifferent stage Differentiation stage Indifferent stage Indifferent stage  Indifferent stage Gonads appear initially as a pair of longitudinal ridges, called the genital or gonadal ridges. They are formed by: 1- proliferation of the celomic epithelium 2- condensation of underlying mesenchyme. 3-Germ cells reside among endoderm cells in the wall of the yolk sac close to the allantois, then migrate by ameboid movement along the dorsal mesentery of the hindgut to invade the genital ridges in the sixth week of development. Indifferent stage  Indifferent stage Shortly before and during arrival of primordial germ cells: the epithelium of the genital ridge proliferates, and epithelial cells penetrate the underlying mesenchyme. Here they form several irregularly shaped cords, called primitive sex cords. These cords are connected to surface epithelium,  Development of Testis Y- chromosome SRY gene encodes the testis-determining factor Development of Testis  Development of Testis - primitive sex cords continue to proliferate and penetrate deep into the medulla to form the medullary (testis) cords. - the cords break up into a network of tiny cell strands that later give rise to tubules of the rete test. - During further development, a dense layer of fibrous connective tissue, the tunica albuginea, separates the testis cords from the surface epithelium. - In the fourth month, the testis cords become horseshoe-shaped, and their extremities are continuous with those of the rete testis. - Testis cords remain solid until puberty, when they acquire a lumen, thus forming the seminiferous tububles.  Cells in the seminiferous tubules - 1- Primordial germ cells (endodermal origin) - 2- Sertoli cells (derived from surface epithelium) - 3- Interstitial cells of Leydig (testosterone-secreting cells)(mesodermal): derived from the original mesenchyme of the gonadal ridge, lie between the testis cord  Descent of the testis  Testis is first at level of 1st lumbar segment  At 3rd m: Descent of the testis starts.  At 6th m: It reaches close to deep inguinal ring.  At 7th m: It reaches deep inguinal ring  At 8th m: It transverses inguinal canal  At 9th m: It reaches superficial inguinal ring  Shortly before birth: It reaches the scrotum  So the testis has internal then external descent  Descent of the testis  Gubernaculum is a a fibromuscular cord connecting the testis to the base of scrotum, it shortened during descent of the testis.  Descent of the testis Processus vaginalis is a peritoneal protrusion passes through the inguinal canal to reach scrotum. After descent, the part of the processus inside the inguinal canal is obliterated and fibrosed forming the vistigue processus vaginalis. The part inside the scrotum remains patent to form tunica vaginalis.  Congenital anomalies 1- Undescended testis (cryptorchism): Descent may be arrested at any point; it can be abdominal or inguinal – it can lead to infertility and malignancy 2- Ectopic testis: after passing out of superficial inguinal ring testis may pass to ectopic site: It can be in the root of penis, perineum or upper part of front of the thigh it is due to abnormal attachment of gubernaculum  Anomalies 3- Congenital indirect (oblique) inguinal hernia: it is due to persistent processus vaginalis 4- Congenital hydrocele: it is due to accumulation of fluid in tunica vaginalis 5- Hydrocele of the cord: it is due to persistent middle part of processus vaginalis to form swelling due to accumulation of fluid Development of the Ovary Development of the Ovary  Development of the Ovary - Primitive sex cords dissociate into irregular cell clusters, containing groups of primitive germ cells. - These clusters occupy the medullary part of the ovary later, they disappear and are replaced by a vascular stroma that forms the ovarian medulla. - The surface epithelium of the female gonad, continues to proliferate. In the seventh week, it gives rise to a second generation of cords, cortical cords, which penetrate the underlying mesenchyme but remain close to the surface..  Development of the Ovary - In the third month, these cords split into isolated cell clusters. - Cells in these clusters continue to proliferate and begin to surround each oogonium with a layer of epithelial cells called follicular cells. - Together, the oogonia and follicular cells constitute a primordial follicle. - Surface epithelium is reduced to a single layer of germinal epithelium. - Mesoderm underneath the surface epithelium condenses to form thin tunica albugenia.  Descent of the ovary  The ovary is first opposite to 1st lumbar segment  By the 3rd m, ovary starts to descend to be just below the rim of the true pelvis So, the ovary has an internal descent only  Descent of the ovary Cranially: cranial genital ligament forms the suspensory ligament of the ovary Caudally: caudal genital ligament gubernaculm connects the ovary to labium majus but connected to lateral angle of uterus in its course  Part of gubernaculum between the uterus and the ovary forms ovarian ligament, will that between the uterus and labium forms round ligament that pass through inguinal canal  Congenial anomalies  Ectopic position of the ovary (rare):  It is due to failure of gubernaculum to attach to the lateral angle of the uterus.  It leads to external descend of the ovary.  Ovary may lie in inguinal canal or even in labium majus.  Development of genital ducts Indifferent stage Differentiation stage Indifferent stage  Indifferent stage In 6th week: 1- Mesonephric duct (Wolffian) and tubules. Mesonephric tubules are 3 groups: cranial, middle and caudal 2- Paramesonephric (Mullerian) ducts: It arises from the epithelium on the anterolateral surface of the urogenital ridge. It has 3 parts: 1- Upper (cranial) part: it descends vertically lateral to the mesonephric duct. 2- middle part: it crosses horizontally infront of the mesonephric duct. 3- lower (caudal) part: it descends vertically medial to the mesonephric duct and close to the mullerian duct of the other side. Cranially, the duct opens into the abdominal cavity with a funnel-like structure. Caudally the tip of the combined ducts projects into the posterior wall of the urogenital sinus, where it causes a small swelling, the sinus (Mullerian) tubercle Development of male genital ducts  Development of male genital ducts Mesonephric tubules: Middle group(epigenital tubules): They establish contact with cords of the rete testis and form the efferent ductules. Cranial group: Degenerate forming appendix of epididymis. Caudal group: Degenerates forming paradidymis. Mesonephric duct: - Upper part: it is greatly elongated attenuated and coiled to form epididymis. - The greater part: is thickened to form the vas deferens - Behind the neck of urinary bladder: an outgrowth from the mesonephric duct forms the seminal vesicle - The part of the ducts beyond the seminal vesicles is the ejaculatory duct. Paramesonephric ducts: They degenerate except for a small portion at their cranial ends, the appendix testis Development of female genital ducts Development of female genital ducts  Development of female genital ducts Mesonephric tubules: Degenerate to form paroophoron, epoophoron, vesicular appendage and Gartener’s duct (remnants in broad ligament) Paramesonephric duct: - Cranial vertical and middle horizontal parts: Form Fallopian tubes - Caudal vertical parts: from both sides fuse to form the uterine canal - This uterine canal form uterus and upper third of the vagina Lower two thirds of the vagina: Two solid evaginations grow out from the sinus tubercle, called sinovaginal bulbs, they proliferate and form a solid vaginal plate. This plate canalizes to form the lower two thirds of the vagina. -The lumen of the vagina remains separated from that of the urogenital sinus by a thin tissue plate, the hymen. It usually develops a small opening during perinatal life. Congenital anomalies Congenital anomalies  Congenital anomalies  Complete degeneration of Mullerian ducts: leading to failure of development of all female ducts  They are due to lack of fusion or canalization of female ducts Horns: - Arcuate uterus: bulging of inner wall of fundus. - Uterus bicornis unicollis: 2 uteri + 1 cervix. - Uterus bicornis bicollis: 2 uteri + 2 cervices. - Uterus didelphys: double uterus and vagina. - Uterus unicornis unicollis: atrophy of Mullerian duct at one side. B) Septa: - Bipartite uterus: uterus is partially divided in two parts by a septum - Septate uterus: Complete division by a septum - Septate uterus and/or vagina Canalization: - Imperforated hymen: may lead to hematocolopos, then hematometria. - Cervical atresia - Vaginal atresia: due to failure of development of failure of fusion of sinu- vaginal bulbs. Fistulae: If Mullerian ducts open in: - Anorectal canal: leads to rectovaginal fistula - Vesicouretheral canal: leads to vesicovaginal fistula Others: Gartener’s cyst: a cyst at the vaginal wall due to unobliteration of a part of mesonepheric duct  Development of external genitalia Indifferent stage Differentiation stage  Indifferent stage Cloacal membrane urogenital membrane anal membrane  Indifferent stage At 3rd week, migrating mesoderm forms elevation at both sides of cloacal membrane called cloacal fold - Cranial ends of cloacal folds fuse forming genital tubercle - Another pair of folds appear lateral to cloacal folds called genital swellings or labioscrotal folds). At 6th week, cloacal membrane is divided by urorectal septum into urogenital membrane (anteriorly) and anal membrane (posteriorly). - cloacal folds are divided into urethral folds (anteriorly) and anal folds (posteriorly) Development of male external genitalia X  Development of male external genitalia Under the influence of androgens secreted by the fetal testes: - Genital tubercle shows rapid elongation and called the phallus. - During this elongation, the phallus pulls the urethral folds forward so that they form the lateral walls of the urethral groove. - This groove extends along the ventral aspect of the elongated phallus but does not reach the most distal part, the glans. - The epithelial lining of the groove, which originates in the endoderm, forms the urethral plate. - At the end of the third month, the two urethral folds close over the urethral plate, forming the penile urethra. This canal does not extend to the tip of the phallus.  Development of male external genitalia - This most distal portion of the urethra is formed during the fourth month, when ectodermal cells from the tip of the glans penetrate inward and form a short epithelial cord. This cord later obtains a lumen, thus forming the external urethral meatus. - The genital swellings, known in the male as the scrotal swellings, arise in the inguinal region. With further development, they move caudally, and each swelling then makes up half of the scrotum. - Mesodermal condensations within the penis develop the 3 erectile tissues 2 corpora cavernosa and 1 corpus spongiosum  Anomalies Hypospadius: Urethral orifice at ventral aspect – due to partial failure of fusion of urethral folds and margins of urethral groove – complete failure causes that the urethral orifice is a longitudinal slit along ventral aspects of scrotum and penis Epispadius: Urethral orifice is at dorsum of penis- due to growth of the genital tubercle at the region of urorectal septum- commonly present in cases of ectopia vesicae Absence of penis: Due to failure of growth of genital tubercle Micropenis Megalopenis Bifid penis: if genital tubercle splits Development of female external genitalia  Development of female external genitalia - The genital tubercle elongates only slightly and forms the clitoris. - Urethral folds do not fuse, as in the male, but develop into the labia minora. - Genital swellings enlarge and form the labia majora. - The urogenital groove is open and forms the vestibule.