development of the genital system Flashcards
what are the uro-genital organs developed from?
intermediate mesoderm
when does the embryo show male/female characteristics
7th week
where do gonads appear (early embryology)
appear as a pair of longitudinal Genital ridges; each ridge is located on one the medial side of the mesonephric ridge; with the latter they form the Urogenital Ridges.
what two ducts form in early embryology
o Paramesonephric Duct (Mullerian duct) arises on the anterolateral surface of the Urogenital Ridge.
o Mesonephric duct (Wolffian duct) develops just dorsal to the paramesonephric duct
what happens at the indifferent gonad stage
- During the arrival of Germ cells to the genital ridge, the epithelium of the ridge proliferates and some of them penetrate the underlying mesenchyme and form a number of irregular shaped cords, the primitive sex cords: these cords are connected to surface epithelium.
- These events take place similarly in the male and female.
describe the differentiation of the gonad
- Male germ cells carry XY sex chromosomes
- The key to sexual dimorphism is the Y chromosome, which contains a gene called the Sex – Determining Region on Y (SRY)
- The SRY protein is called, Testis – Determining Factor and under its influence, male development takes place.
- In the absence of Testis-Determining factor, female development takes place.
describe the development of the male gonads
- The primitive sex cords continue to proliferate and penetrate deep into the medulla to form the cords of the testis. cords break up forming the rete testis
- A dense layer of fibrous connective tissue develops under the surface epithelium of genital ridge - Tunica Albuginea.
- The genital ridge is now called testis
what do the testis contain at around 16 weeks
- The migrated primordial germ cells which will form spermatogonia
- Sertoli cells - assist in the development of spermatogonia
- Leydig cells - secrete testosterone
summary of male development
Y chromosome -> SRY gene -> Promotes testis-determining factor -> genital ridge develops into testis -> Leydig cells (testosterone) -> Mesonephric duct develops -> Sertoli cells (mullerian inhibiting factor) -> degeneration of the paramesonephric ducts
describe the development of the female gonads
- Primitive sex cords dissociate into irregular cell clusters. contain groups of primitive germ cells, occupy the medullary part of the ovary - eventually completely disappear
- 7th week the surface epithelium of the ovary gives rise to a second generation of cords which penetrate the underlying mesenchyme.
- 3rd month: cords split into isolated cell Clusters which surround each Oogonium with a layer of epithelial cells - Follicular cells
describe the role of Estrogen on development
involved in differentiation of Mullerian Ducts in to
Uterine Tubes Cervix
Uterus Upper 2/3 Vagina
stimulates the development of the external genitalia which develop from the Urogenital sinus: lower 1/3 vagina, labia majora & minora, clitoris
summary of female development
absence of Y chromosome -> no gonadal hormone influence -> genital ridge develops into ovarian tissue by default -> absence of testosterone -> mesonephric ducts degenerate -> absence of mullerian-inhibiting factor -> paramesonephric ducts develop
describe the development of the uterus and the uterine tubes
• The upper 2/3 of Mullerian ducts -> uterine tubes,
• The lower 1/3 fuse -> body and cervix of uterus and upper part of the vagina.
• broad transverse pelvic fold extending from uterus to the lateral pelvic wall - Broad Ligament of Uterus. The uterine tubes lie in its upper border and the ovary lies on its posterior surface.
• Mesenchyme that surrounds the Uterus and cervix
-> Myometrium and Perimetrium
describe the development of the vagina
- Upper part of the vagina with vaginal fornices are derived from caudal part of the uterine canal (Mullerian tubercle).
- Lower part of the vagina is derived from the Urogenital Sinus.
- It starts as development of two solid evaginations - Sinovaginal Buds, proliferate and form a solid vaginal Plate.
- By the 5th month, the vaginal outgrowth is entirely canalized.
- The lumen of the vagina remains separated from the urogenital sinus by a thin tissue plate- Hymen, this usually develops a small opening during perinatal life
describe the development of the female external genitalia
- Estrogen stimulates development
- The genital tubercle slightly elongated and forms the clitoris.
- Urethral folds do not fuse and form the labia minora.
- Genital swellings form labia majora.
- The urethral groove remains open and forms the vestibule.
