Embryology of the Urogenital Systems Flashcards
What does intermediate mesoderm separate from during folding and forms urogenital ridge?
From lateral and paraxial mesoderm
What do urinary and genital systems develop from?
Intermediate mesoderm of trilaminar disc
What forms pronephros?
Nonfunctional cervical nephrotomes
When do nephrotomes transitory and regress?
By week 5
When does a second primitive kidney develop?
During the 4th week
What follows the development of the second primitive kidney during the 4th week?
- functional glomeruli develops
- mesonephric tubules form
- mesonphric duct opens into cloaca
mesonephros are present and functional during what weeks?
from weeks 6-10
What happens to mesonephros after week 10?
It degenerates except for: the duct system or some vestigial structures
What does the duct system that remains contributes to?
Part of the male genital system (ductus deferens)
What part of the mesonephros remains after week 10 in females?
Some vestigial structures in the female
What does renogenesis involve?
Involves a process of reciprocal induction, which is retinoic acid dependent
What establishes a “renogenic” region within the intermediate mesoderm in the tail of the embryo?
The cranial-caudal patterning
What is the renogenic mesoderm called?
Metanephric blastema
What is the function of the metanephric blastema?
Secretes growth factors that induce growth of the ureteric bud from the caudal portion of the mesonephric duct
When the Ureteric bud proliferates how does it respond?
By secreting growth factors that stimulates proliferation and then differentiation of the metanephric blastema
What does the metanephric blastema differentiate into after stimulation from ureteric bud?
Into glomeruli and kidney tubules
What may cause inhibition of ureteric bud growth and renal hypoplasia or agenesis?
Perturbations in any aspect of renogenesis events (mutations of either metanephric or ureteric factors or disruption of retinoic acid signaling)
In contrast to inhibition of ureteric bud growth, what else can occur during renogenesis?
Duplication or over proliferation of structures
When does blood plasma from glomerular capillaries begin to be filtered?
By week 10
When urine is produced In utero, what is the primary function?
It is not to clear waste (placenta) but to supplement production of amniotic fluid
What may indicate bilateral renal agenesis or urethral obstruction?
Oligohydramnios: insufficient amount of amniotic fluid
Where are kidneys formed? Why do they move during development?
In the pelvis but ascend to lumbar region with progressive revascularization from common iliac and aorta
What enters the kidney independently from the primary renal vessels?
Aberrant renal vessels
Aberrant renal vessels entering the kidney occurs how often in the population? Where do the vessels originate?
These occur in approximately 10% of individuals and 98% arise from the abdominal aorta
When do aberrant renal vessels cause a problem vs pose little issues?
Most enter the renal pelvis and pose little problems
Aberrant renal arteries that enter the upper or lower poles of the kidney may post problems
Aberrant arteries to the inferior pole of the kidney (4-6%) may be the cause for what?
Obstruction of the ureter and may cause an intermittent or continuous obstruction to urinary drainage from the renal pelvis
When can potter syndrome be diagnosed?
In utero diagnosis
Who is the first to survive Potter’s syndrome diagnosis?
Abigail who now undergoes nightly dialysis prior to transplant. She went through experimental treatment, which involved intrauterine fluid injections to facilitate growth and development
What prevents normal renal rotation?
Renal fusion
What kind of blood supply do renal fusion usually have?
Abnormal blood supply usually from middle sacral or common iliac arteries
What may also be crossed with/without fusion?
Ectopic kidney
Pelvic kidney and horseshoe kidney are examples of _____
Renal fusion
What type of renal fusion is most common?
Horseshoe kidney
90% fused at lower pole
Usually found inferior to inferior mesenteric artery
What is Wilms’ tumor?
Cancer of the kidney
Wilms’ tumor usually affects who?
Children under the age of 5
What causes Wilms’ tumor?
Mutation in the WT1 gene
3 month-old previously healthy boy presented with hematuria. A renal ultrasound, and subsequent chest, abdomen, and pelvis CT exam demonstrated a large heterogeneous right renal mass: diagnosis?
Wilms’ tumor
Describe the steps of the urinary bladder
- cloaca divided by the urorectal septum
- Dorsal (inferior) portion develops into the rectum and anal canal
- The ventral (superior) portion develops into the bladder and urogenital sinus
What does the bladder and urogenital sinus give rise to?
The bladder and lower urogenital tracts
What bladder and urogenital tracts are present in males?
Prosstatic and penile urethrae
What bladder and lower urogenital tracts are present in females?
Urethra and lower vagina
Mesonephric duct and ureteric bud incorporation into posterior wall of urinary bladder occurs between what weeks?
4-6
What do ureteric buds open into?
The bladder wall
Where does the mesonephric ducts open?
More inferiorly into the pelvic urethra.
What does not open into the bladder?
Ductus deferens
What does the triangular region of the incorporated mesonephric duct incorporated in the bladder wall form?
The trigone
Bladder is continuous (superiorly/inferiorly) with allantois?
Superiolry
What should happen with the allantois?
Collapse and become the urachus
What abnormalities can happen with the urachus?
- may remain paten throughout its length: urachal fistula
- patent only at an end: urachal sinus
- remnants of urachal lumen may also give rise to urachal cysts: usually present as an abdominal mass
When is the genotype of the embryo established?
At fertilization
How long does the embryo remain in undifferentiated state?
Week 1-6
When does phenotypic sexual differentiation begin?
Week 7
When can male and female external genitalia be recognized?
Week 12
When is the phenotypic differentiation complete?
Week 20
Fetal sex is encoded where?
On the sex determining region of the Y chromosome (SRY)
What triggers male development?
Synthesis of SRY protein (testis-determining factor, TDF)
If SRY protein is not expressed what happens?
whether absent or defective, female path is followed
What is the basic (default) developmental pathway?
Female
What cannot be expressed in order for female path to be followed?
TDF
Describe the male development pathway
- activation of SRY gene
- TDF
- Differentiation of biopotential gonad into testis
- Sertoli cell differentiation
- Mullerian inhibitory substance/factor
- regression of paramesonephric (mullerian) ducts
- urogenital sinus, forrmed from division of the cloaca
How many pairs of genital ducts are present in both sexes during development?
two
When are both pairs of genital ducts present during development?
The indifferent stage
Mesonephric ducts play the most important role in (male/female)
male
Paramesonephric ducts play the most important role in (male/female)
female
The gonads develop from what three tissues?
epithelium of intraembryonic coelom
intermediate mesoderm
primordial germ cells
What invades the dorsal mesentery and migrate to urogenital ridges?
primordial germ cells from mesoderm of yolk sac
What are aggregates of supporting cells (homorne secreting cells)?
Primary sex cords
When primary sex cords develop what doe gonads now have?
An outer cortex and inner medulla
What does the phallus become?
Clitoris or penis
What do (uro)genital folds become?
Labis minora or shaft of the penis
What does the labioscrotal (genital) wellings become?
Either labis majora or scrotum
What are some paramesonephric duct anomalies?
- uterus didelphys with double vagina
- Uterus arcuatus
- Uterus bicornis
- Uterus bicorni unicollis: 1 redimentary horn
- Atresia of cervix
- Atresia of vagina
What can result in cervical or vaginal atresia?
Partial or total atresia of the distal portion of both ductus
What can have persistence of paramesonephric ductus if the circulating levels of AMH are low or there is an abnormal response to normal AMH?
46, XY
Failure of the paramesonephric ducts to develop can result in what?
Missing uterine tubes, uterus and variable malformations of the upper portion of the vagina
What is MRKH or Mayer-Rokitansky-Kuster-Hauser-Syndrome?
Missing uterine tubes, uterus and variable malformations of the upper portion of the vagina
What is hypospadias?
incomplete fusion of the urethral folds
where does the urethra open onto in males in hypospadias?
The ventral aspect of the penis
What can hypospadias result from?
From inadequate androgen production or inadequate receptor sites for DHT
What are the types of hypospadias from moderate to severe?
- glandular
- penile
- penoscrotal
- perineal
What do females (46, XX) with severe forms of adrenal hyperplasia have what?
Ambiguous genitalia at birth due to excess adrenal androgen production in utero
Female intersex
What does abiguous genitalia range from?
Ranges from complete fusion of the labioscrotal folds and a phallic urethra to only clitoromegaly, partial fusion of the labioscrotal folds, or both
Do intersex females have ovaries?
there are no abnormalities of ovaries
What is androgen insensitivity syndrome (AIS) - complete ?
An x-linked disorder in which receptors remain unresponsive to androgens
Despite normal levels of testosterone, the male fetus fails to masculinise
External genitalia are feminine: internally they posses non-functional undescended testes
Some males may tend to be feminine in gender and behaviour (maybe)
What can happen at puberty with someone with AIS?
Secondary female sexual characteristics may appear due to estradiol from testosterone aromatization
What is common to perform on males with AIS?
gonadectomies at puberty and for them to receive hormone therapy, to be reared as female
The degree of feminization of AIS depends on what?
Upon affected androgens and the amount of residua receptor function
What is 5-ARD?
Autosomal recessive condition resulting in the inability to convert testosterone to the more physiologically active dihydrotestosterone (DHT)
If someone has 5-ARD what happens?
Because DHT is required for the normal masculinization of the external genitalia in utero, genetic males with 5-ARD are born with ambiguous genitalia (underdevelopment of penis and scrotum or psuedovaginal perineoscrotal hypspadias)
What is 5-ARD often misdiagnosed as?
AIS
What derivatives are normal in 5-ARD?
Derivatives of mesonephric duct are normal
What is the third gender called?
Guevedoche or Machinhembras
first woman, then man
