Development of Repro System Flashcards
When is sex determined?
At fertilization
Three groups of organs in a reproductive systems
Gonads
Reproductive ducts
External Genitalia
The presence of what appears to influence sexual differentiation in the male direction?
Androgens (monohormone theory)
Androgen alone is unsuccessful at promoting regression of female ducts. What second factor is needed?
Mullerian Inhibiting Factor
A glycoportein secreted by the testis until age 10
Receptrs are on paramesonephric or mullerian ducts that are precursors to oviducts, uterus and part of vagina
What is the indifferent stage of development?
Between 4-6 weeks when primordia of reproductive system begin to form and are morphologically indistinct with respect to sex differentiation
Where do the gonads form?
In the ventromedial portion of the nephrogenic ridge as a proliferation of the overlying coelomic epithelium –> nephrogenic ridge becomes the urogenital ridge (UG)
Three cell types that contribute to the formation of gonads
- germinal cells
- supporting cells
- interstitial or steroid producing cells
Primordial germ cells
Form the stem cells for gamete production
Migrate to gonad during weeks 4-5, proliferate and continue to divide during weeks 5-6
Organizing stimulus
Supporting cells
Sertoli - M
Granulosa - F
Originate from cord-like proliferations of the coelomic epithelium overlying the gonad primordium
Interstitial cells
Leydig - M
Theca - F
Originate from mesonephric mesenchyme cells
Upon stimulation they synthesize and secrete steroid hormones
Gonad attachments with surrounding mesenchymal tissues
Cranially - suspensory ligament –> develops vascular supply
Caudally - gubernaculum –> attaches the primitive gonad to ventral body wall
Duct systems that develop during the indifferent stage
- Mesonephric ducts: Wolffian ducts (week 4)
2. Paramesonephric ducts: Mullerian ducts (week 6)
Paramesonephric ducts
Inferior 1/3 fuses together in the midline to form Uterovaginal primordium –> around week 8-9 causes a swelling at the back wall forming the UG sinus = Sinus Tubercle
Paramesonephric ducts open into UG sinus
How do the external genitalia form?
They originate as swellings in the caudal region of the embryo adjacent to the cloaca
Parts of external genitalia
- Genital tubercle
- Urethral folds
- Labioscrotal swellings
Summary of Indifferent Stage
Weeks 4-6
Sexually determined but sexually undifferentiated embryo
Has a pair of undifferentiated gonads
Two sets of ducts - mesonephric and paramesonephric
Set of elevations and folds around the cloacal membrane
What is the SRY gene and where is it located?
Short arm of chromosome Y
Encodes DNA binding protein –> testicular determining factor
Expressed during week 6 causing cells of genital ridge to differentiate into sertoli cells (begin to express Sox-9)
When does testicular organization occur?
Weeks 6-7
Summary of testicular organization
Sertoli cells surround primordial germ cells - inhibit progression to meiosis –> organize into testicular cords (develop a lumen at puberty = seminiferous tubules)
Sertoli cells organize into a network of channels = Rete Testis
Sertoli cells begin to secrete MIF
When are Leydig cells produced?
At 8 weeks, sertoli cells secrete signals to recruit mesenchyme cells to become Leydig (interstitial) cells
Begin to secrete testosterone during weeks 8-9
When does testis relocation occur?
From week 7 to 9 months
Driven by shortening of gubernaculum
When does ovarian organization occur?
7-10th week (later than in the testis)
Primordial germ cells enter meiotic prophase and are committed to oogenesis
When stimulates the production of follicle cells?
Oocyte production of FIGalpha –> stimulates supporting cells to differentiate into follicle cells
Follicle cells produce Meiosis Inhibiting factor that arrests oocyte int meiotic prophase
What is required for normal ovarian development?
Two X chromosomes
