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
When does the ovary descend into the pelvis?
Week 12
What male ducts are derived from mesonephric ducts and tubules?
Ducts = Duct of epididymis, ductus deferens, ejaculatory ducts Tubules = efferent ductules
How does the prostate develop?
At week 10 – epithelial buds of endoderm from the prostatic urethra forms gland tissue
How do the seminal vesicles form?
As outgrowths of the mesonephric duct just before it enters the forming prostate gland
What happens to the paramesonephric ducts in the male?
Suppressed by MIS which causes their atrophy
What happens to the mesonephric ducts in females?
Absence of testosterone causes their atrophy
What do the paramesonephric ducts become in the female?
Unfused cranial 2/3 become the oviducts
Inferior caudal 1/3 become uterovaginal primordium –> most becomes the uterus; vagina comes from both PD and UG sinus
How is the vagina formed?
During weeks 6-7, the inferior part of the uterovaginal primordium contacts the posterior wall of the UG sinus -> stimulates formation of sinus tubercle
Paired, solid outgrowths (sinovaginal bulbs) extend dorsally from the tubercle pushing the PD superiorly
Bulbs fuse to make vaginal plate that becomes canalized by week 20
What is the hymen?
membrane that separates the UG sinus from the lumen of the vagina
What are the three parts of the UG sinus?
Vesicle (superior)
Pelvic (intermediate)
Phallic (inferior)
What does the pelvic part of UG sinus give rise to in males vs females?
Males: Pelvic part –> epithelial lining of the distal prostatic urethra and membranous urethra
Females: forms epithelial lining of the inferior part of the vagina
What does the phallic part of the UG sinus give rise to in males vs females?
Males –> epithelial lining of penile urethra
Females –> epithelial lining of vestibule
What gives rise to the penis?
The genital tubercle – elongates during the indifferent stage to become the phallus (begins during week 6)
What forms the scrotum?
In the 4th month, perineal area elongates and labioscrotal swellings fuse ventrally
What results in hypospadias?
Incomplete fusion of the urethral folds
What is associated with epispadius?
Bladder exstrophy
How does the female external genitalia form?
Absence of androgens –> perineal area does not elongate
Phallus bends inferiorly to become clitorus
Urethral folds remain unfused –> labia minora
Labioscrotal swellings remain unfused –> labia majora
Stimulated by esrogens
