Lecture 3 Development Of The Repro System Flashcards
What does the urogenital system develop from?
Intermediate mesoderm
Development of the reproductive system
- Indifferent gonads develop from primordial germ cells
- The indifferent gonads can differentiate into the testis or ovary and the indifferent external genitalia depending on the presence of testosterone.
- The testis or ovary have indifferent duct systems and differentiate into either the epididymis and vas deferens for the testis or uterus, Fallopian tubes and part of the vagina for the ovary
Which structure is shared between the GI tract, Repro tract and urinary tract?
The cloaca - dilated end of the hindgut closed to the outside by the cloacal membrane
Urogenital ridge
Region of intermediate mesoderm giving rise to the embryonic kidney and gonad
Where is the gonad derived from?
From intermediate mesoderm and the primordial germ cells
Primordial germ cells
Arise in the yolk sac and migrate when developed into the retroperitoneum, along the dorsal mesentery
What drives male development?
SRY gene present in the Y chromosome
Male development
Gonad: testis
Hormone: Testosterone (androgens) and Mullerian inhibiting hormone
Internal genitalia: mesonephric duct (wolffian)
Female development
Gonad: ovary
Hormone: oestrogen
Internal genitalia: paramesonephric duct (Müllerian duct)
Why does the wolffian mesonephric duct develop in men?
Due to androgens released in the testis
Why is there no mullerian (paramesonephric) duct in men
Due to mullerian inhibiting hormone released by the testis that suppresses the paramesonephric duct (mullerian)
Where do the paramesonephric and mesonephric ducts end?
At the urogenital sinus part of the cloaca
Ectopic androgen effects in women
Wolffian and Müllerian ducts
Persistence of wolffian mesonephric duct even in women due to androgen
No testis therefore no MIH therefore persistence of the mullerian paramesonephric duct
Androgen insensitivity syndrome in men
No wolffian mesonephric duct
No mullerian paramesonephric duct
Receptors are insensitive to testosterone therefore Wolffian ducts degenerate
Testes present that secrete MIH therefore mullerian paramesonephric ducts degenerate
Mesonephric wolffian duct
First acts as the duct for the embryonic kidney in both males and females
Drains into the urogenital sinus
When the kidney develops it becomes surplus
It is converted into the vas deferens and epididymis
Migrates with the testis as it descends to the scrotum
Urogenital sinus
Becomes the urinary bladder
Paramesonephric Müllerian duct
Invagination of the urogenital ridge epithelium
Cranially: opens into the abdominal cavity
Caudally: makes contact with the cloaca urogenital sinus
Undifferentiated external genitalia components
Genital tubercle
Genital folds
Genital swellings
External genitalia of men development
The genital tubercle elongates into the glans penis
The genital folds fuse to form the spongy urethra (penile raphe)
The genital swellings become the scrotum
Influenced by testes derived androgen hormones
External genitalia of women development
The genital folds develop into the labia minora
The genital tubercle develops into the clitoris
The genital swellings develop into the labia majora
The urethra opens into the vestibule
Descent of the gonad
Gubernaculum attaches the gonad inferiorly to the labioscrotal folds
Abdominal pelvic cavity increases
Gonads descend
Descent of testes
- The gubernaculum attaches to the inferior pole of the testes
- It contacts and shortens dragging the testes down to the scrotum causing the testes to invaginate into the layers of the abdominal wall
- Forms the inguinal canal
- The testes pass through the processus vaginalis
- Once the testes are in the scrotum, the gubernaculum becomes the scrotal ligament and the processus vaginalis becomes the tunica vaginalis
Covering of the spermatic cord
Internal spermatic fascia - transversalis fascia
Cremasteric fascia - internal oblique aopneurosis
External spermatic fascia - external oblique aponeurosis
Descent of the ovary
- Gubernaculum attaches the ovary inferiorly to the labioscrotal folds
- The ovary descends to the pelvis
- The developed uterus prevents further descent
- The remnants of the gubernaculum are the round ligament and ligament of the ovary
