8. Embryology of the Reproductive Tract 2

divisions of the urogenital ridge

• nephrogenic cord→ urinary system

• genital ridge

  • gonads

  • ductal system

what is the paramesonephric duct also known as

• mullerian duct

what structures are within the testes

• tubules

  • seminiferous tubules

  • rete testis

• leydig cells→ produce testosterone

• sertoli cells→ produce anti-mullerian hormone

• sperm

what germ layer are the structures within the testes derived from

• sperm→ primordial germ cells

• tubules, leydig cells, sertoli cells→ mesoderm derived

components of the male ductal system

• efferent ductules

• epididymis

• vas deferens

• seminal vesicles

• ejaculatory duct

affect of hormones on growth of ducts

• testosterone stimulates mesonephric duct to grow

• paramesonephric duct regresses due to AMH production

insertion of seminal vesicles and vas deferens

• have common entry to prostatic urethra→ ejaculatory duct

what do bladder and urethra form

• urogenital sinus portion of the cloaca

ductal system→ month 9

• testes in their final position within the scrotum

• gubernaculum is significantly shorter

where are elements of the ovaries derived from

• follicular cells→ mesoderm

• oocytes→ primordial germ cells

growth of the ducts in females

• no sertoli cells- AMH→ paramesonephric duct persists

• without testosterone production, mesonephric ducts regress

what does the mullerian ducts give rise to

• uterine tubes

• uterus

• upper 2/3 vagina

where are paramesonephric ducts in relation to the bladder

• sat dorsally

• means uterus forms posterior to bladder

• gubernaculum aids descent of the ovaries to the pelvic region

what does the gubernaculum split into

• ovarian ligament

• round ligament of the uterus→ anchored in labia majora

when do ovaries reach their final position

• month 9

causes of abnormalities of the uterus

• failure of paramesonephric ducts to fuse

• failure of uterine septum to degenerate

• failure of one paramesonephric duct to elongate

persistent mullerian duct syndrome

• affects genetic males

• mutation in AMH gene→ no AMH production= paramesonephric ducts persist

• both mesonephric and paramesonephric duct derivatives develop

• normal male external genitalia but associated with cryptorchidism

formation of the lower portion of the vagina

• urogenital sinus develops sinovaginal bulbs

  • fuse with paramesonephric ducts to form lower third of the vaginal canal

separation of the cloaca

• separates to form urogenital sinus and rectum

• around week 4→ both males and females have the same formation in the urogenital sinus

indifferent stage of external genitalia

• mesoderm cells migrate to surround cloacal membrane→ form elevated cloacal folds

• cloacal folds unite anteriorly to form genital tube→ future penis/ clitoris

• cloacal folds divide into anal and urethral divisions

• genital swellings appear next to urethral folds→ future scrotum/labia majora

what is differentiation of external genitalia reliant on

• presence of androgen

differentiation of external genitalia→ males

• elongation of urogenital tubercle into phallus

• labioscrotal folds move caudally→ become scrotum

• month 9

  • urethral groove has fused to form penile urethra

  • labioscrotal swellings have united in midline to form scrotal septum

hypospadias

• incomplete fusion of urethral folds→ urethra opens on ventral surface of penis/scrotum

• difficulty urinating

• can be repaired surgically using foreskin

epispadias

• urethral opening on dorsal surface of penis

• genital tubercle develops posteriorly in urogenital sinus

• generally occurs with exstrophy of the bladder

differentiation into female genitalia

• occurs under influence of oestrogen

• genital tubercle elongates slightly to form clitoris

• urethral folds do not fuse→ form labia majora

• genital swellings form labia majora

• urogenital groove remains open