Week 6: Urogenital Embryology Flashcards
mesophrenic ducts
form cranially to caudally and then fuse with the developing bladder
What germ layer do the reproductive and urinary systems develop from?
mesoderm (lateral to the somites)
pronephros
(first kidney)
develops in cervical region and then regresses (never functions)
mesonephros
(middle kidney)
develops in the thoracic to lumbar region (functions)
Interim kidney first trimester
metanephros
the third and definitive kidney; buds off the mesonephric duct
2 parts of the metanephros
excretory system and collecting system
collecting system of the metanephros develops from
the ureteric bud that sprouts from the mesonephric duct
excretory system of the metanephros develops from
the intermediate mesoderm cells that surround the ureteric bud, forming the metanephric blastema (metanephric mesenchyme)
collecting system of the metanephros consists of
ureter, renal pelvis, calycers, and 1-3 million collecting ducts
excretory system of the metanephros consists of
nephrons
nephrons
“the functional unit of the kidneys”
they are vesicles or tubules that produce urine in the process of removing waste and excess substances from the blood
how are glomaruli (capillary tufts) formed?
capillaries grow into the distal end of each nephron to form glomeruli
Due to growth of the body, kidneys shift where?
they shift from the pelvis, cranially
called ascension
horseshoe kidney
sometimes inferior ends of the kidneys fuse. They ascend until caught under the IMA
Bifed ureter
(aka double ureter)
the ureteric bud bifurcates before the metanephric blastema forms
ectopic kidney
kidney crosses to the other side during ascension
pelvic kidney
a kidney that doesn’t ascend completely
thoracic kidney
it ascends too far
congenital anomalies of the urinary system can lead to
urine blockage, infection, or kidney stones
multiple renal arteries
kidney is supplied by several arteries off the aorta during ascension; usually they degenerate. If these accessory arteries are damaged or ligated, part of the kidney can become ischemic
when do the kidneys become functional?
by 12 weeks
bilateral renal agenesis
results in oligohydramnios, causing compression of the fetus by the uterus. It leads to Potter sequence
potter sequence
a result of oligohydramnios
limb deformities, wrinkly, dry skin, facial anomalies (wide set eyes with infra-orbital skin creases, beak nose, recessed chin, and low set ears), and pulmonary hypoplasia
cloaca
the caudal end of the hindgut from which the urinary bladder forms
urorectal septum
(mesoderm)
divides the cloaca into the urogenital sinus and the anorectal canal
urogenital sinus becomes
the bladder and urethra
allantois
connects the apex of the bladder to the umbilicus
urachus
the fibrous cord that remains from the allantois
urachus gets covered by peritoneum and becomes the
median umbilical ligament on the posterior aspect of the anterior abdominal wall
if the urorectal septum doesn’t form correctly
hindgut abnormalities can occur
imperforate anus
a potential consequence of improper formation of urorectal septum
urorectal fistula
a potential consequence of improper formation of urorectal septum
it’s either between rectum and bladder or rectum and urethra
anal or anorectal agenesis
a potential consequence of improper formation of urorectal septum
persistence of a lumen in the urachus can cause
a urachal fistula (urine can come out of the umbilicus), a urachal cyst, or a urachal sinus
primordial germ cells (PGCs)
- originate from epiblast
* migrate from yolk sac into intermediate mesoderm medial to the mesonephros causing formation of the gonadal ridge
primitive or primary sex cords
formed when the epithelium covering gonadal ride (mesodermal) invades the underlying mesoderm
paramesonephric ducts
a second pair of ducts that forms lateral to the mesonephric ducts
“indifferent stage”
week 6 of embryo before differential of gonads into testes or ovaries
Mesonephric (Wolffian) ducts
become epididymis, vas deferens, and seminal vescicles
paramesonephric (Mullerian) ducts
become the uterus, uterine tubes, and upper vagina
somatic support cells in the XX gonad produce
“anti-testes” factrors (Wnt4)
Wnt4 causes
maintenance of oocyte number and oocytes
fig alpha causes somatic support cells to differentiate into follicle cells
why do paramesonphric ducts persist in female differentiation?
there is no MIS (mullerian inhibiting substance)
why do mesonephric ducts and tubules regress in female differentiation?
no testosterone
Somatic support cells in XY gonad have SRY gene that produce
TDF (testis determining factor)
SRY is the sex determining region on the Y chromosome
AMH (anti-mullerian hormone) or MIS (Mullerian inhibiting substance) cause
paramesonephric (Mullerian) ducts to degenerate in males
mesenchymal cells in gonadal ridge differentiate into what during male development?
leydig cells
testosterone causes
differentiation of epididymis, vas deferens, and seminal vescicles from mesonephric duct; and male brain differentiation
5-alpha reductase causes
conversion of testosterone to dihydrotestosterone, which causes male development (penis, scrotum, prostate)
testosterone surge at puberty causes
maturation of seminiferous tubules, spermatogenesis, and other pubertal changes
in male, primitive sex cord becomes
testis cords
in male, at the hilum, cords form
rete testis
in male mesonephric tubules become
efferent ducts
in male mesonephric duct becomes
epididymis, ductus deferens, and siminal vesicle
in female, primitive sex cords become
somatic support cells then follicle cells
in female, follicle cells surround
the PCGs (primordial germ cells) (oogonia)
In female, paramesonephric ducts become
uterine tube, uterus, and upper vagina
prostatic utricle is
remnant of mullerian duct in males
gartner’s cyst is
remnant of mesonephric duct in females
in males prostate and bulbourethral glands bud off
the urethra
in males the seminal vesicles bud off the
mesonephric duct
trigone
formed in males when the lower end of the mesonephric ducts are incorporated into the bladder. It also results in the vas deferens wrapping over the ureter after testis descend
in female, uterus and upper vagina form when
caudal ends of the paramesonephric ducts fuse
uterine tubes are
the remaining unfused paramesonephric ducts
the lower vagina forms from
sinovaginal bulbs (proliferation of endodermal tissue on the posterior wall of urogenital sinus)
uterine and vaginal anomalies result from
problems with development of the paramesonephric ducts
diethylstilbestrol (DES)
a synthetic estrogen used to prevent miscarriage from 1947-71
resulted in higher risk of uterine anomalies and clear cell carcinoma of the vagina in offspring
uterine didelphys
- caused by no fusion of the paramesonephric ducts
* double uterus
bicornuate uterus
- caused by partial fusion of the paramesonephric ducts
* fundus is indented
septated uterus
- medial walls of paramesonephric ducts fail to resorb
* 2 endometrial cavities
unicornuate uterus
- incomplete development of one paramesonephric duct
* uterus connects to one ovary
cervical atresia
paramesonephric ducts resorb too much
at indifferentiated stage, embryo has
genital tubercle, urogentical folds, labioscrotal swellings, and anal folds
in female, genital tubercle becomes
clitoris
in female, urogenital folds form
labia minora
in female, labioscrotal swelling form
labia majora
in male, urogenital folds
fuse
in male, genital tubercle elongates to become
shaft and glans of penis
in male, urogenital (urethral) fold
fusion also forms penile urethra
in male distal urethral forms from
canalization of urethral endoderm extending into the glans
in male, labioscrotal swellings
fuse to form the scrotum
What might cause gonads not to develop at all?
if the germ cells from the epiblast do not migrate to the gonadal ridges
testis determining factor (TDF) causes formation of
Sertoli cells and Leydig cells
Sertoli Cells produce
Mullerian inhibiting substance (MIS)
(penile) Hypospadias
- urethral folds don’t fuse completely or form abnormal canalization of the urethral plate within the glans penis, causing a VENTRAL (on the underside of penis) opening of urethra
- 10% of the time it’s accompanied by chriptorchidism
(penile) epispadia
- occurs when the urethral orifice opens on the DORSAL side of the penis. Usually associated with exstrophy of the bladder
- much less common than hypospadia
exstrophy of bladder
bladder is outside the ventral/anterior body wall due to a defect in the ventral body wall (ie it doesn’t form completely during body folding, this is very rare)
descent of gonads
- gonads form on posterior body wall and must descend to their anatomical position
- as they descend, gubrnaculum shortens, and the processus vaginalis is pushed along in front
what ligaments attach to gonads
- attached cranially to diaphragm by a suspensory ligament
* attached caudally to labioscrotal swellings by a fibrous cord called gubernaculum
processus vaginalis
(vaginal process) an outpouching of parietal peritoneum that forms the inguinal canal
spermatic cord
in males, layers of abdominal wall are pushed into the scrotum and form the 3 layers of the spermatic fascia in the spermatic cord
processus vaginalis closes to become
tunica vaginalis
when do testes reach the deep inguinal ring?
- around 4 months of embryonic development
* they descend through the inguinal canal shortly before (or right after) birth
cryptorchidism
- when the testis fails to descend
* occurs in 1-4% of live male births and increases the risk of infertility and testicular cancer
orchipexy
surgical correction of cryptorchidism
testicular torsion
- twisting of spermatic cord that crimps the testicular artery
- an anomaly associated with the processus vaginalis
testicular hydrocele
- fluid between parietal and visceral layers of the tunica vaginalis
- an anomaly associated with the processus vaginalis
indirect (congenital) inguinal hernia
- 75% of inguinal hernias
- occurs lateral to inferior epigastric vessels
- passes through deep inguinal ring and inguinal canal as a protrusion along the spermatic cord, and lies within the internal spermatic fascia
ovaries descend
- into the pelvis, but don’t enter labia majora
* gubernaculum becomes the ligament of the ovary and the round ligament of the uterus
round ligament of the uterus
transverses the inguinal canal into the labia majora
broad ligament in females forms
when the peritoneal folds covering the paramesonephric ducts fuse
suspensory ligament (of the ovary)
contains the ovarian vessels
MDs don’t LIe
- for remembering direct versus indirect hernias
- Direct are Medial to inferior epigastric vessels
- Indirect are Lateral
