Embryology of the Reproductive System Flashcards
When does the reproductive organogenetic period occur?
Starts in week four
Extends beyond week eight, even postnatally as organs are not fully mature until puberty
What is the gonadal ridge formed from?
The medial part of the mesonephric ridge
How are the primitive sex cords formed?
Cells from gonadal ridge become thickened
How is the indifferent gonad formed?
During week six, cells from the yolk sac migrate via the dorsal mesentery and imbed in the primitive sex cords, forming the indifferent gonad
How is the paramesonephric duct formed?
Formed via invagination of the epithelium of the mesonephros
Where do the paramesonephric ducts form?
Formed next to the mesonephros, and come together inferiorly to form the cloaca.
They form lateral to the developing gonads and caudally project into the dorsal wall of the urogenital sinus
What are the alternative names for the mesonephric and paramesonephric ducts?
Mesonephric duct- Wolffian duct
Paramesonephric duct- Mullerian duct
What processes occur in males following the formation of the indifferent gonad?
- Gonad forms testis
- Mesonephric duct develops into epididymis, vas deferens, seminal vesicle,
- Paramesonephric duct degenerates
- Urogenital sinus forms bladder, urethra; and prostate
What processes occur in females following the formation of the indifferent gonad?
- Gonad forms the ovary
- Mesonephric duct degenerates
- Paramesonephric duct forms fallopian tube, uterus, cervix part of vagina
- Urogenital sinus forms bladder and lower part of vagina
How does the indifferent gonad know whether to form into testes or ovaries?
Due to presence of sex-determining region Y (SRY) gene on the Y chromosome
SRY codes for testis-determining facor (TDF) gene
Primordial supporting cells in sex cords express SRY, which transforms them into Sertoli cells that produce Mullerian inhibiting substance (MIS) which transforms the mesenchymal cells into Leydig cells and paramesonephric duct degenerates
Testosterone produced by Leydig cells cause development of male external genitalia
If there is no SRY gene the indifferent gonad develops into an ovary by default
How are the seminal vesicles formed?
From an outgrowth from caudal end of mesonephric duct
How is the prostate formed?
From an outgrowth from the urethra (from urogenital sinus)
How are ovaries formed?
Ovarian development starts when primary sex cords regenerate
Secondary sex cords have formed from surface epithelium by week 10
Primordial germ cells then become incorporated into them, before budding off with a single layer of cortical cord cells to form the primordial follicles
Follicles undergo mitosis to form more follicles
All follicles formed by month 7
How do the mesonpehric and paramesonephric ducts operate in females?
Lack of testosterone causes mesonephros to regress
Paramesonephric duct persists to form female genital tract
How does the paramesonephric duct correspond to the female genital tract?
Cranial end becomes ovaries
Caudal end becomes uterus and superior part of vagina
Urogenital sinus forms inferior part of vagina
