Embryology of the Reproductive System Flashcards
Where does the reproductive system originate from?
Intermediate mesoderm gives rise to the urinary and reproductive systems
Explain the meaning of indifferent gonads
Initially, the gonads begin as indifferent structures; male/female differentiation is triggered by germ cells
Describe migration of the germ cells
Migrate from the yolk sac to the genital ridge (~week 4); eventually, the gonads become populated with germ cells, which become assoc. with support cells
2 ducts form:
• Mesonephric duct (AKA Wolffian duct) - degenerates in females
• Paramesonephric duct (AKA Mullerian duct) - important for female reproductive system; it degenerates in males
Explain the influence when the indifferent gonads develop into the ovaries
If female (44 + XX), there is an absence of the Y chromosome; the indifferent gonads differentiate into the ovaries
The sex cords degenerate and the cortical cords develop; there is no tunica albuginea
Explain the influence when the indifferent gonads develop into the testes
If male (44 + XY), there is a Y influence; the indifferent gonads differentiate into the testes
The sex cords develop, i.e: no cortical cords form; there is a thick tunica albuginea
What is required for male development?
Required expression of the Sex-determining Region of Y (SRY)
This causes continued development of the primitive sex cords, to form the testis cords; also gives rise to the rete testis, which forms a connection with the hilum of the testis (allows exit of sperm)
NOTE - the rete testis has formed by month 4
When do the seminiferous tubules form?
The testis cords are solid and do not form seminiferous tubules until puberty
What happens to the support cells, around the germ cells, in the testis?
Differentiate into the following cells
Leydig cells - produce testosterone, which stimulates:
• Mesonephric ducts, leading to development of the efferent ductules, epididymis, vas deferens and seminal vesicles)
• Production of dihydrotestosterone and development of the external genitalia (growth of penis, scrotum and prostate)
Sertioli cells - produce Mullerian inhibiting substance, leading to suppression of the paramesonephric ducts
Explain how the testes descend into the scrotum
Controlled by the gubernaculum, which shortens and pulls the testes down into the deep inguinal ring, by the 3rd month
At the 7th month, the gubernaculum once again shortens, pulling the testes into the scrotum
How does the tunica vaginalis form?
The vaginal process loses its connection with the peritoneal cavity and becomes the tunica vaginalis
What happens to the gubernaculum, once the testes are in the scrotum?
Retained and anchors the testis in the scrotum; if it is not retained, the testis is free in the scrotum and can tort
What coverings are picked up by the testis, during its descent into the scrotum?
INTERNAL SPERMATIC FASCIA from the covering of transversalis fascia
CREMASTERIC FASCIA from the covering of skeletal muscle fibres from the internal oblique
EXTERNAL SPERMATIC FASCIA from the covering of external oblique aponeurosis
Steps in female development?
- Degeneration of primitive cords and development of cortical cords
- Descent of ovaries
- Development of the uterus
- Ligaments of the ovary
Explain how the ovaries develop in the female
Primitive sex cords form and then degenerate
The mesonephric ducts (AKA Wolffian ducts) also degenerate in females, whereas the paramesonephric ducts (AKA Mullerian ducts) persist
Oestrogen leads to:
• Stimulation of paramesonephric ducts, forming the uterine tube, uterus and upper potion of the vagina
• Development of external genitalia (labia, clitoris and lower portion of the vagina)
Explain how the ovaries descend
Paramesonephric ducts meet in the midline, forming the broad ligament of the uterus
The ducts are attached to the gubernaculum, pulling the ovaries down into this peritoneal fold (broad ligament)
How does the uterus develop?
Paramesonephric ducts make contact with the wall of the urogenital sinus (9 weeks); this point of contact leads to wall proliferation and the formation of sinovaginal bulbs (swellings)
These begin to cavitate, forming the uterine cavity (end of the 3rd month)
Components of the vagina?
Upper 1//3rd - formed from the paramesonephric ducts
Lower 2/3rds - formed from the sinovaginal bulbs
Abnormalities of the uterus?
Uterine didelphys with double vagina - tips of paramesonephric ducts have touched the urogenital sinus and there have been 2 areas of proliferatio, leading to 2 uterine cavities and 2 vaginas
Uterus arcuatus - indentation at the top of the uterine cavity; this is a remnant of the septum
Uterus bicornis - 2 uterine cavities with a single vagina
Uterus bicornis unicollis - single vagina, single cervix and double, single-horned uteruses which are partially fused
Atresia of cervix
Atresia of vagina
Formation of the external genitalia?
3rd week - cloacal folds form and fuse cranially to form genital tubercle
6th week - cloacal membrane divided into urogenital and anal membranes; cloacal folds also divide into urethral and anal folds
The genital swellings form the following:
• In males - scrotum
• In females - labia major
Anomalies of urogenital system and hindgut?
Common origin of the urogenital system and the rectum / anal canal means that there may be connections and fistulae between them
