L10 Urogenital system
L10 Urogenital system
ORGANOGENESIS OF THE
This lecture will discuss:
The derivatives of the intermediate mesoderm
the formation of the nephric systems
the formation of the genital ducts
the formation of the gonads
the formation of the external urinary and genital
Overview of organogenesis of the urogenital organs
Urinary and reproductive systems
are closely associated in
Two systems have common origin
from the urogenital ridge(UGR) and
have homologous structures.
Internal genital duct system is
derived from the foetal urinary system.
Malformation of one system affects
The UGR is longitudinal swelling in (genital ridge)
dorsolateral side of the abdomen
UGR--> formed mostly from
--non-segmented intermediate mesoderm
Lateral UGR(nephrogenic plate)
forms urinary organs and internal
Ventromedial UGR is genital ridge,
The Urogenital ridge
The nephrogenic plate differentiates in a rostral to
caudal direction and bilaterally. The three nephric
systems appear in recapitulating sequence during
(functional in lower fishes)
Tubules(higher fishes and
Sequence of development of the metanephros(1)
Metanephros develops at
somites 26-28 from 2 precursors
--> ureteric bud(UB)
and metanephrogenic mass
Formation UB and MM is by
reciprocal inductive interactions
between the tissues.
The diverticulum forms caudal of
the existing mesonephric duct and
grows and into the MM at the
UB forms the duct system
MM forms nephrons
The ureteric bud branches as it
grows towards the metanephrogenic
Morphogenesis of the ureteric bud(2)
The ureteric bud forms the duct system
The metanephrogenic mass forms the
nephrons by nephrogenesis.
Nephrogenesis and differentiation of
the ureteric bud are co-ordinated
Dichotomous branching pattern of the
ureteric bud is species specific.
Branching of simple unilobar/
unipyramidal kidneys(dog,horse) the
proximal end dilates into a renal pelvis with
collecting ducts at the tip
In multipyramidal kidneys(ox) ureter
bifurcates into 2 major calyces and several
minor calyces then collecting ducts
Kidney of dog
Kidney of ox
Development of the metanephros(3)
Stages in nephrogenesis.
Solid cluster of metanephrogenic mass forms(A) and
hollows into a renal vesicle(B) with epithelial lining this
elongates into metanephric tubules (C).
Proliferation,elongation of the MM dependent upon
reciprocal tissue interactions using several molecular
signalstubules grow and form parts of nephrons.
Ureteric bud by
Nephrogenesis. Formation of glomerulus
Proximal tube forms PCT, end
dilates and invaginates to form the
Distal tube forms DCT and fuses
with the collecting tubule.
BC invaded by the
glomerulusforms renal corpuscle
Large numbers of nephrons form
Interstitial connective tissue
forms between nephrons and thick
fibrous capsule surrounds the
Nephrogenesis ceases at birth,
continues for 1-3 wks in the dog
Fusion, elongation of nephric tubules and
association with capillary, to form of
Proximal tubule of nephron
Distal tubule of nephron
Fused basal lamina
Structure of renal
capsule and glomerulus
Glial derived neurotrophic factor(GDNF) regulates
growth and branching of ureteric bud
A. Wild type mouse has normal
branching of ureteric bud
B. GDNF gene knock out mouse
Gonadogenesis(1). The bipotential gonad
Gonadogenesis occurs at the genital ridge initiated by 2 simultaneous
events:(i).Formation of gonadal cords
Epithelium from degenerate mesonephric nephrons invade genital
ridge.And form network of epithelial cords
(ii).Migration of primordial germ cells.
PGC are endodermal cells, migrate from the yolk sac into the bipotential
gonad.The gonad has a central medulla and a peripheral cortex,
surrounded by coelomic epithelium.
PGC arrive at the genital
ridge at 21 days cat and
PGC, forming gonadal
Red arrows shows gene regulation
Primary sex determination at fertilisation
(i). genetic sex: XY, XX
(ii).Y chromosomes encodes testisdetermining
secretion of foetal hormones by
interstitial cells[(Sertoli and
Leydig(M),theca cells(F)] secondary
Regression of Mullerian
•Differentiation of Wolffian duct into
Male genital ducts
•Descent of testis
Germ cells and Sertoli cells
concentrate in the testicular cords Mullerian duct
The cortex develops a thick fibrous Interstitium
Testicular cords form loops
(seminiferous tubules) and interconnect
with mesonephric tubules to form
In the absence of the Y
chromosome in primordial
concentrate in the cortex
degenerates. The remnants
form the vascular,
lymphatic and nervous
Meiosis begins and is
arrested at diplotene of
prophase I when epithelia
surround germ cells
forming primordial follicles.
Formation of the urogenital sinus(UGS)
Cloaca is common opening
for the urinary and digestive
systems and bounded caudally
by the the cloacal membrane.
Formation of the UGS
begins with division of the
cloaca by the mesodermal
urorectal septum separating
cloaca into dorsal anus and
ventral urogenital parts,
bounded by anal and urogenital
forming the anal and urogenital
Schematic diagram of lateral view.15days dog
Differentiation of female and male ducts
The UGS opens into the
allantoic cavity via the urachus
It divides into a cranial pelvic Bipotential
region and caudal phallic region.
--The cranial UGS expands into
the bladder and urethra in both Indifferent Bladder
--The caudal UGS forms penile
urethra in male and vagina in
ducts form female genital ducts, Female Bladder
fuse caudally to form uterus and Efferent ducts
Ductus deferens Rectum
In male(C) the
Wolffian/mesonephric ducts form
epididymis and ductus deferens.
Renal agenesislack of development.
Dysplasiaabnormal development of nephrons and collecting ducts, form
Hypoplasiaagenesis of ureterhydronephrosis.
Ectopic kidneys and ureters.
Polycystic kidneysfailure of nephrons to join collecting ducts?
Rectovaginal constriction at rectovaginal junctionhereditary
Outpockecting of bladder when urachus fails to close.
Cryptorchidismfailure of normal descent of testis.
Mesonephric or paramesonephric duct abnormalitiesstenotic/aplasia of
Pseudohermaphroditegonads of one sex and external gentalia of the
opposite sex, hormonal factors.
True hermaphrodites is chromosomal abnormality during meiosis when the Y
chromosome gets a fragment of the X chromosome, the gonad or ovo-testes
gonad formed has both ovarian and testicular tissue. And hormones of both
sexes are produced resulting in abnormal external genitalia.
Freemartin cattle intersexuality, a genotypic female(XX) born with normal
male co-twin due to fused placental vessels resulting in the transport of foetal
androgens to the female.
The urinary system and genital system are derived from the intermediate
mesoderm,the nephrogenic plate and genital ridge of the urogenital ridge.
Three kidneys develops in rapid successionpronephros, mesonephros
and metanephros in cranial-caudal direction.
Pronephros is of limited function in mammals is inducer mesonephros.
The metanephros forms from two precursorsthe ureteric bud and the
metanephrogenic mass.Development of the metanephros requires
reciprocal tissue interaction using several molecular signals.
Sex determination is dependent upon interaction of several
factorsGenetic sex, gonadal sex, hormonal action and phenotypic sex.
Germ cells are endodermal, the other tissues are mesodermal. Early in
development, germ cells migrate from the yolk sac to the genital ridge.
Development of the urogenital system is dependent on molecular signals.
The external urinary and genital organs are formed from the cloaca and
The Wolffian and Mullerian ducts form the adult male and female ducts
1. Gilbert, Scott.F(2003). Developmental Biology. 6th.Edition.
pp447-461, 523-540, 548-561, Sinauer Associate. Massachusetts.
2. McGeady, T.A., Quinn, P.J., Fitzpatrick, E.S., & Rayan, M.T., (2006).
Veterinary Embryology. Page 233-241; 244-265
3. Noden, M. and de Lahunta(1985). The Embryology of Domestic
Animals, pp 312-341, 349-355 Williams and Wilkins, London.