Development of the urogenital system

Location of the pronephros, mesonephros and metanephros

 Connection between aorta and mesonephric tubules, and Differentiation of the intermedierm mesoderm between intraembryonic coelom and tubules established into nephrotome and mesonephric tubules  External and internal glomeruli are formed  Laterally a longitudinal duct collects the urine from the tubules: this is the Wolffian-duct (or mesonephric duct)

An outgrowth from the mesonephric duct, the ureteric bud growing towards metanephros. With time their distal end will be incorporated into the dorsal wall of the urogenital sinus.

1

Development of kidney

ca su

bo eq Ureteric bud reaches the metanephrogenic tissue

Ureteric bud dilates, forms renal pelvis, major and minor calyces, collecting tubules

Wolffian-duct (blue) and ureteric bud (yelow) will be partly incorporated into urogenital sinus, thus this site is mesodermal derived  trigonum vesicae 2

Formation of tubular and collecting system

 Ureteric bud dilates, forms renal pelvis, major and minor calyces, collecting tubules  Crossing movement: ascent of metanephros, descent of the gonad /blue: mesonephros and mesonephric duct, red: gonad, black: metanephros/  Parts of the urogenital sinus: urachus, urinary bladder, urethra

Metanephrogenic tissue around ureteric bud

Urogenital ridge: - laterally is the mesonephros (with the glomerulus, excretory tubule, mesonephric duct, paramesonephric duct) - medially is the gonad Connection between the excretory units (blue) of the metanephrogenic tissue with collecting tubular system (yellow) which arrived from ureteric bud

Renal corpuscle, glomerulus, Bowman’s capsule, proximal convoluted tubule, loop of Henle, distal convoluted tubule (from the excretory tubules), and the collecting tubule (from the ureteric bud)

3

Gonadal development

 A genital ridge appears medially on the urogenital ridge

 Next to the Wolffian (or mesonephric) duct is the Müllerian (or paramesonephric ) duct

Primordial germ cells (originated from the epiblast) migrate through primitive streak, then in the wall of the yolk sac and primitive gut, finally through the dorsal mesentery they reach the primitive gonads

Primitive sex cords develop due to the penetration of epithelial cells into the underlying mesenchyme, the primordial germ cells move between them  indifferent gonad has been established 4

Differentiation of the testis, ovaries and their ducts

XY XX spermatozoa primordial germ cells indifferent gonad primordial germ cells ova SRY gene tubuli semineferi, sex cords sex cords follicular cells Sertoli cells

Müllerian paramesonephric duct suppressed inhibiting substance (Sertoli cells) paramesonephric ducts stimulated

estrogens testis ovary mesonephric ducts (maternal and stimulated placental sources) testosterone (Leydig cells) external genitalia stimulated external genitalia stimulated

develop medullary cords degenerate

Ø cortical cords develop thick tunica albuginea Ø

efferent ductules, epoophoron, mesonephric tubules paradidymis paroophoron epididymis, Wolffian-duct Gartner’s duct deferent duct appendix uterine tube, appendix testis, testis Müllerian-duct uterus, uterus masculinus part of vagina

5

Uterus types and descent of the testis

bo su eq

ca ho or

Descent of the testis through inguinal channel into scrotum, directed by the gubernaculum testis

6

External genital organs

In females uterine tube, uterus and cranial portion of vagina have been formed from Müllerian-duct, whilst caudal part and vestibule of the vagina develops from the urogenital sinus’s vaginal plate

In males mesonephric duct gives rise the seminal vesicles and ampulla ductus deferentis, and caudal part of the urogenital sinus transforms into pelvic and penile urethra, prostate and bulbourethral gland

genital tubercle, urogenital and anal folds genital tubercle and cloacal folds - next to urogenital fold genital (labioscrotal) swelling appears

genital tubercle  phallus, glans of the penis genital tubercle  clitoris, urogenital fold fuse  urethral groove  penile urethra urogenital folds  labia (minora) of the vulva genital swellings fuse above the urethral groove  scrotum genital swellings Ø  no labia majora

7

Developmental anomalies

complete partial double ureter double ureter possible sites for pelvic kidney an ectopic ureter

urachal fistula urachal cyst urachal sinus horseshoe kidney

Genotype problems: - X0 (Turner’s syndrome): mostly in horse. Infertile, anoestrus female, hypoplastic inner and outer genitals - XXY (Klinefelter’s syndrome): infertile males with hypoplastic testes. Eg.: tortoiseshell and tricolor cats Phenotype problems: - pseudohermaphroditism: internal and external genitalia are ambiguous. Eg.: androgen effect during gestation - true hermaphroditism: both ovarian and testicular tissues are present - freemartinism: genotypic female (XX) animal which born with a co-twin male (XY) and his androgens affect her. Cattle. - testicular feminization syndrome: genetic males with internal testes and external female genitalia. Prevalent in pigs - mesonephric ducts abnormalities: - stenosis or aplasia of the epididymidis or ductus deferens - paradidymidis: persistent mesonephric tubules caudal to the efferent ductules - epoophoron, paroophoron: remnants of the cranial parts of the mesonephric tubules - Gartner’s duct: remnant of the caudal parts of the mesonephric duct. Common in cow, sow and cat - paramesonephric ducts abnormalities: - appendix testis, uterus masculinus (utriculus prostaticus): remnant of the paramesonephric duct - persistent Müllerian duct syndrome: uterus and uterine tubes in males. Eg.: Basset hound, Miniature Schnauzer - uterus duplex (uterus didelphys): each duct enters the vagina separately - cryptorchidism: failure of one or both testicles to descend into the scrotum. One of the most common disorder - congenital preputial stenosis (phimosis): narrowing of the preputial orifice - hypospadia: urethra opens onto the ventral surface of the penis

8