Development Of Reproductive Systems 2 Flashcards
When does development of external organs start?
• Starts in week 4
• Remains undifferentiated until
week 7
- Begins to be distinguishable after week 9
- Fully differentiated after week 12
Describe the indifferent stage
Genital tubercle—> primordial phallus (cranial end of the cloacal membrane)
Cloacal membrane —> urogenital membrane(midline)
Urethral folds—> urogenital folds
Labioscrotal swellings —> labioscrotal swellings
The urorectal septum unites with the cloacal membrane dividing it into the UG membrane and anal membrane
Summarize the development of the male genitalia
Phallus elongates to form the penis Urogenital folds form the lateral walls of the urethral groove on the ventral surface of the developing penis
Urethral plate (endoderm from the phallic part of the UG sinus) is in the floor of the urethral groove
Testosterone produced by the leydig cells of the fetal testis.
Converted to Dihydrotestosterone by 5-alpha-reductase. Dihydrotestosterone is necessary for masculinization of developing external genitalia
The urethral folds begin fusing together posteriorly, and will eventually fuse completely along the ventral aspect of the penis
The labioscrotal swellings also begin fusing together posteriorly (and normally fuse completely to form the scrotum)
The penis continues to elongate
The urethral folds fuse on the ventral surface of the penis forming the spongy (penile) urethra and the penile raphe (where surface ectoderm meets in the midline)
How do the corpus cavernosum develop?
The corpus cavernosum and spongiosum develop from the mesenchyme in the phallus
Labioscrotal folds continue to grow together and fuse to form the scrotum
How is the spongy urethra formed?
An ectodermal ingrowth from the tip of the glans penis forms a cord extending to the root of the penis to join the spongy urethra.
The cord canalizes to form the terminal part of the urethra and external orifice.
Circular ectodermal ingrowth at the glans forms the prepuce when it breaks down.
What is Hypospadias?
The most common anomaly of penis (1:125). External urethral orifice is on the ventral surface of the glans (glanular hypospadias) or body of the penis (penile hypospadias)(80%). Results from failure of urethral folds to unite due to inadequate production of androgens by the fetal testes/inadequate receptor sites.
In perineal hypospadias, there is failure of fusion of both the urethral folds and the labioscrotal folds.
What is the Epispadias?
Urethra opens on the dorsal surface of penis
Often associated with exstrophy of the bladder
May result from inadequate ectodermal-mesenchymal interactions during development of the genital tubercle
[1 in 30,000]
Summarize development of the female genitalia
NO TESTOSTERONE
Elongation of the phallus DECREASES to form the clitoris
Labia minora/vestibule of the vagina are formed both from ectoderm of the urethral folds and endoderm of the UG sinus (phallic part)
NO TESTOSTERONE
Urethral folds fuse posteriorly only, to form the frenulum (posterior commissure) of the labia minora
Labioscrotal swellings only fuse posteriorly to form the posterior labial commissure and anteriorly to form the anterior labial commissure and the mons pubis. Most
parts remain unfused, forming the labia majora
Summarize female external genitalia
Genital tubercle —> clitoris
Urogenital folds do not fuse—> labia majora
Labiosacral swellings do not fuse—> labia majora
What are Ovotesticular DSD (true hermaphroditism)?
Rare and is a condition in which the gonads contain both ovarian and testicular tissue
Chromosomal configuration usually 46,XX
Phenotype may be male or female
Clinically ambiguous genitalia is the reason for investigation
What is 46, XY DSD?
Males who produces inadequate levels of testosterone and AMH in utero
External and internal genital organs vary in appearance due to variable degrees of development
What is 46, XX, DSD?
Females who have been exposed to excessive amounts of androgens in utero = adrenal hyperplasia
Causes masculinization of the external genitalia but no ovarian abnormality
Enlargement of the clitoris, partial fusion of the labia majora, persistent urogenital sinus
What is Androgen insensitivity syndrome (AIS)?
Individuals who appear female but have 46,XY chromosome configuration
Vagina ends blindly, rudimentary or absent uterus and uterine tubes
Testes present in the inguinal canal
Female breast development at puberty External genitalia is female or masculinized Results from cellular resistance to testosterone
What does the mesonephric duct form?
Male-Trigone of bladder, Epididymis, vas deferens, ejaculatory duct & seminal vesicle
Female-Trigone of bladder the rest degenerates
What are the mesonephric tubules formed into?
Male- Efferent ductules of the testis
Female-Degenerate
