Urogenital System Development

kidneys derived from

intermediate mesoderm + coelomic mesothelium = urogenital ridge

coelomic mesothelium - covering of embryonic body cavity

intermediates of kidney formation

1. pronephros

2. mesonephros

3. metanephros → becomes adult kidney

pronephros

consists of 7-8 tubules

nonfunctional

pronephric duct persists as mesonephric duct

mesonephros

functional → produces urine

consists of 70-80 tubules

tubules with glomerulus at one end, connected to the mesonephric duct at the other end

rapidly degenerates (cranial to caudal)

caudal tubules and duct remain to form testicular channels. epididymis, ductus deferens, and contributes to gonad development

metanephros

adult kidney

metanephric diverticulum (ureteric bud) → ureter, renal pelvis, calyxes, and collecting ducts

metanephrogenic mass (mesenchyme) → nephrons (functional unit → produces urine)

metanephric diverticulum grows out into surrounding mesoderm causing metanephrogenic mass to form

nephron formation

not unlimited, cannot produce any more once in adult state

urinary bladder and urethra

urinary bladder develops from an expansion of the urachus and cranial end of the urogenital sinus

urogenital sinus contibutions

• male: pelvic urethra and penile urethra

• female: pelvic urethra, vestibule and caudal vagina

formation of urinary bladder

1. mesonephric duct (dd) enters into urinary bladder, branching off mesonephric duct is the ureter

2. differential growth - ureter and dd have separate tubes

3. differential growth - ureter enters UB, dd enters urethra

renal malformation

agenesis - doesn’t form

dysplasia - abnormal

hypoplasia - underdeveloped

ectopic - differentiates in pelvic area and sometimes fails to ascend to sublumbar, typically non problematic, bad for pregnancy

ectopic ureter

ureter within urethra not UB, drippling urine

more common in female puppies

patent urachus

urachus not closed out at birth - medical management or surgical repair

early in development there is a membrane blocking urethra, normally degenerates to allow urine to flow out into amniotic cavity, urachus closes out once urine has an alternate route out

urachus connects to allantoic cavity, initial conductor for removing urine

indifferent stage of reproductive system

gonad will eventually signal differentiation

paramesonephric duct - present, further develops in females

mesonephric duct - present, further develops in females

testis influence on differentiation

testosterone (Leydig cells)

• mesonephric ducts stimulated → vas deferens, epididymis

• dihydrotestosterone, external genitalia stimulated → growth of penis, scrotum, and prostate (accessory sex glands)

mullerian inhibiting substance (AMH)(Sertoli cells)

• paramesonephric ducts suppressed (“Mullerian duct”)

ovary influence on differentiation

estrogens (maternal and placental)

• paramesonephric ducts stimulated → uterine tube, uterus, cranial portion of vagina

• external genitalia stimulated → labia, clitoris, caudal portion of vagina

mesonephric ducts degenerate in the absence of testosterone

germ cells

primordial germ cells replicate until 100-300 cells then migrate to the genital ridge (area of degenerating mesonephric kidney)

gonadal (genital) ridge

indifferent stage of gonadal development

• gonadal cords formed by disintegrating mesonephric tubules

• germ cells interact with degenerating mesonephric cords

testicular development

mesonephric duct → epididymis and ductus deferens

mesonephric → rete testis and efferent tubules

gonadal cords → seminiferous tubules

paramesonephric duct degenerates

testicular descent

gubernaculum

• attaches to caudal pole of testis and scrotum

• holds developing gonad in position

• mesenchymal CT

  • mesenchymal cells release hyaluronic acid (inc. H2O) causing swelling and enlargement

  • dilates inguinal canal and scrotum

  • decreased [hyaluronic acid] → dec H2O → gubernaculum shrinks drawing testis into scrotum

remnants of the gubernaculum

• ligament of the tail of the epidisymis

• proper ligament of testis

ovarian development

degenerating mesonephric tubules → follicular cells

primordial germ cells in urogenital ridge → egg

female reproductive tract development

paramesonephric duct → uterine tube, horns, body, cervix, and cranial 1/3 → ½ of vagina

urogenital sinus → caudal vagina, vestibule

mesonephric duct degenerates

uterine comparative anatomy

based on paramesonephric duct fusion

primates have a large amount of fusion → very large body

external genitalia - indifferent stage

genital tubercle

• male - penis (glans penis, corpora cavernosa, corpus spongiosum

• female - clitorus (glans clitoris, corpora cavernosa clitoris, bulb of vestibule)

urogenital folds

• male - ventral aspect of penis

• female - labia of the vulva

labioscrotal swellings

• male - scrotum

• female - does not/poorly develops in domestic sp.

development of external genitalia

genital tubercle

cloacal fold (blue) - chared opening with digestive and urogenital system

urogenital fold (red)

labioscrotal swelling (orange)

anus (purple)

hypoplasia (gonad)

few/no germ cells

migration issue or division of PGC issue

cryptorchidism

testis doesn’t descend

gubernaculum issue, only in male

stenosis of the ducts, abnormal fusion

issue with hormone release

hypospadia

open urethra in males

penile part of urethra doesn’t form caudally

penile urethra open to environment

intersex conditions

can be internal or external

XY, testicular feminization, testicles w vulva, increased urogenital distance, due to faulty T receptors on urogenital fold and/or genital tubercle

major events in sexual differentiation

males reproductive tracts start developing sooner than female

freemartin

female born twin to a male

typically twins placental BVs anastomose (join) together so hormones from each twin impacts each other

chimeras

male fertility - affected but less

female fertility - underdeveloped tract

• AMH from male decreases development of paramesonephric duct components

• normal urogenital sinus derivatives

• increased anogenital distance because of increased [T]