Special Embryology 4 - Speaker Deck

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CLOACA (Page 51)

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FATE OF CLOACA: -Uro-rectal septum divides the endodermal cloaca into: ventral primitive urogenital sinus and dorsal ano-rectal canal. -Primitive uro-genital sinus receives the openings of 3 ducts: 2 mesonephric ducts and allantois. -A constriction at the level of enterance of mesonephric ducts divides the sinus into 2 parts: -Cranial vesico-urethral canal. -Caudal defenitive uro-genital sinus.

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Development of Urinary Bladder (Page 52)

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DEVELOPMENT OF URINARY BLADDER ➢It develops from 3 parts: ⚫ Vesico-urethral canal (endodermal): forms most of the bladder. ⚫ Proximal part of allantois (endodermal): forms apex of the bladder, rest of allantois is called urachus. Later the urachus becomes obliterated to be median umbilical ligament. ⚫ Caudal parts of both mesonephric ducts (mesodermal): forms the trigone of the bladder.

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CONGENITAL ANAMALIES ➢Ectopia Vesicae (Exstrophy): due to failure of formation of anterior abdominal wall and anterior wall of urinary bladder. ➢Urachal Fistula: due to failure of obliteration of urachus. ➢Urachal Cyst: failure of obliteration of localized part of urachus. ➢Urachal Sinus: failure of obliteration of distal part of urachus.

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DEVELOPMENT OF GENITAL SYSTEM (Page 103)

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Anatomy of Male Genital System

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Anatomy of Female Genital system

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Development of Gonads (Page 57)

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DEVELOPMENT OF GONADS ➢Genital ridge: It is formed at the 4th week by proliferation of coelomic epithelium, forming genital ridges on both sides of dorsal mesentery and medial to mesonephros. ➢These genital ridges are indifferent in both sexes till the beginning of 7th week when it becomes differentiated into testis or ovary.

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Stages of development of gonads 1- Indifferent gonads: 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. Steps of gonad development: 1- Intermediate mesoderm: forms the genital ridge. 2- Coelomic epithelium: forms sex cords. 3- Primitive (primordial) germ cells: form sperms or ova. These germ cells are formed at 21th day in caudal part of the wall of yolk sac (Hindgut). Germ cells migrate through dorsal mesentery to the gonad (at 6th w.)

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DEVELOPMENT OF TESTIS (page 59)

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DEVELOPMENT OF TESTIS ➢It is developed from 3 sources: ➢1- Genital ridge: bulge of intermediate mesoderm, medial to mesonephros on both sides of dorsal mesentery. It forms fibrous septa and tunica albuginea. ➢2- Coelomic epithelium: multiply to form irregular sex cords. ➢3- Primitive germ cells: appear at wall of hindgut and migrate through dorsal mesentery to genital ridge where they become incorporated in the sex cord (by the 6th week).

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-Sex cords become separated from surface coelomic epithelium to form horse-shoe seminiferous cords. -Seminiferous cord communicate towards hilum of testis to form rete testis which in turn communicate with vasa efferentia (mesonephric tubules). -Seminiferous cords become canalized at puberty. The wall is lined with Sertoli cells (derived from celomic epithelium) and spermatogonia (derived from primordial germ cells). -Interstitial cells of Leydig (derived from original mesenchyme and lie between testis cords).

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-Descend of the testis: -The lower pole of testis is connected to scrotum by gubernaculum which contracts pulling testis to scrotum. -It begins development at level of 1st lumbar vertebera. -Factors affecting descent: -Shortening of gubernaculum. -Hormonal (androgen and MIS). -Increased intra-abdominal pressure. -At 3rd month, it lies in iliac fossa. -At 7th month, it lies in inguinal canal. -At 8th month, it lies in superficial inguinal ring. -At 9th month, it lies in the scrotum.

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Processus vaginalis is a peritoneal protrusion that precedes the descend of testis to form the inguinal canal and coverings of spermatic cord. -It becomes obliterated, after descend of testis except the caudal part which is called tunica vaginalis which covers testis with parietal and visceral layers. - Caudal mesonephric ligament remains as ligamentum testis while connective tissue around processus vaginalis remains as scrotal ligament.

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Causes of Descend of testis: -Elongation of upper part of posterior abdominal wall. -Growth of abdominal viscera with increase intra- abdominal pressure. -Contraction of gubernaculum under effect of gonadotrophins.

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Congenital Anomalies of Testis (Page 61)

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A- Abnormal formation: 1- Gonadal dysgenesis. 2- Klinefelter syndrom (47, XXY) 3- Hermaphrodites (intersex): True or pseudo. B- Abnormal Descent: 1- Undescended testis (Cryptorchism) 2- Ectopic testis C- Anomalies of processus vaginalis: 1- Congenital hydrocele. 2- Congenital inguinal hernia.

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DEVELOPMENT OF OVARY (Page 63)

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DEVELOPMENT OF OVARY ➢It is developed from 3 sources: ➢ 1-Genital ridge (part of intermediate mesoderm) that forms fibrous tissue (capsule & stroma) of the ovary. ➢ 2-Coelomic epithelium forms 2 generations of sex cords; medullary which degenerate forming medulla then cortical that persists as follicular cells of primordial follicles. ➢ 3-Primirtive germ cells migrate from wall of hindgut through dorsal mesentery to reach gonads at the 6th week. Germ cells become incorporated in the defenitive sex cords which become broken into clusters of cells (primary oocyte and surrounded with follicular cells) which are called primordial follicles.

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Descent of the ovary: -Firstly it lies on posterior abdominal wall at the level of first lumbar vertebra. -It descends to the pelvic cavity by pulling of gubernaculum which is a fibromuscular cord that extends from lower pole of ovary to labia majora (female external genital organ). - The gubernaculum remains as ovarian ligament (from ovary to uterus) and round ligament (from uterus to labia majora). Congenital Anomalies: 1- Gonadal disgenesis: Absent oocytes and ovaries appear as streak gonads. 2- Ovarian hypoplasia: low number of primordial follicles. 3- XY-female gonadal dysgenesis (Mutant SRY gene). 4- Female pseudo-hermaphrodite: Ovary is present but external genitalia looks like that of male.

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DEVELOPMENT OF GENITAL DUCTS (Page 65) MESONEPHRIC & PARAMESONEPHRIC DUCT

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PARAMESONEPHRIC DUCT ➢Two ducts which are formed by evagination of coelomic epithelium. ➢Cranial end of the duct communicates with coelomic cavity. ➢It has 3 parts: ⚫ Cranial vertical part which lies lateral to mesonephric duct. ⚫ Middle horizontal part which is ventral to mesonephric duct. ⚫ Caudal vertical part which is medial to mesonephric duct. They are blind caudal ends which lie in contact with the back of defenitive uro-genital sinus.

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Utero-vaginal canal: -It is the caudal fused parts of paramesonephric ducts. The septum between the ducts disappears to form a single canal known as utero-vaginal canal. -This canal forms uterus and upper part of vagina. -The upper and middle parts of paramesonephric ducts form uterine tubes. -The cranial end of paramesonephric ducts remain communicating with coelomic cavity. -The caudal part of the vagina is developed from Müllerian tubercle.

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Müllerian Tubercle: -Endodermal proliferation of posterior wall of defenitive urogenital sinus at site of contact of caudal blind ends of paramesonephric ducts. -Upwards growth of müllerian tubercle will form 2 sino-vaginal bulbs which unite together to form vaginal plate. -Vaginal plate canalizes to form lower part of vagina. -Hymen is formed at the junction between developing lower part of vagina and back of defenitive uro-genital sinus. Then hymen becomes perforated. -In males, paramesonephric duct persists as appendix of testis and prostatic utericle.

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Congenital Anomalies A- Failure of fusion between 2 paramesonephric ducts: - Double uterus and vagina. - Double uterus and single vagina. - Double uterus, single cervix and single vagina. - Septate uterus. - Arcuate uterus.

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B- Incomplete development of one uterine tube: -Unicornuate uterus with rudimentary horn. C- Failure or incomplete canalization of paramesonephric ducts: - Atresia of cervix. -Atresia of vagina. -Imperforate hymen.

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