Embryology Of The Urogenital System Flashcards
The nephrogenic cord forms 3 primitive kidneys. What are these kidneys?
- pronephric system
- mesonephric system
- metanephric system
Describe the proneprhros.
- nonfunctional cervical nephrotomes
- transitory and regresses by week 5
Describe the formation and function if the mesonephros.
- during 4th week, a second primitive kidney develops (present and functional from weeks 6-10)
- functional glomeruli develop
- mesonephric tubules form
- mesonephric duct opens into cloaca
After week 10 the mesonephros degenerates and leaves what behind?
- will contribute to part of the male genital system (ductus deferens)
- some vestigial structures in the female
Which primitive kidney forms the anatomical kidney?
-metanephros
What are the steps of renogenesis?
- involves a process of reciprocal induction, which I’d RA dependent
- cranial-caudal patterning establishes a renogenic region within the intermediate mesoderm in the tail of the embryo
- the renogenic mesoderm is the metanephric blastema
- the metanephric blastema secrets growth factors that induce growth of the ureteric bud from the caudal portion of the mesonephric duct
- the ureteric bud proliferates and responds by secreting growth factors that stimulates proliferation and then differentiation of the metanephric blastema into glomeruli and kidney tubules
- perturbations in any aspect of these inductive events may cause inhibition of ureteric bud growth and renal hypoplasia or agenesis
- conversely, duplication of overproliferation of structures can also occur
What are the functions of the metanephros?
-blood plasma from glomerular capillaries begins to be filtered by 10th week
-urine is produced, but the primary function is not to clear waste but to supplement production of amniotic fluid
+oligohydramnios: insufficient amount of amniotic fluid caused by bilateral renal agenesis or urethral obstruction
What are accessory renal vessels?
- kidneys are. Formed. In pelvis but ascent to lumbar. Region with progressive revascularization from common iliac and aorta
- aberrant renal vessels enter the kidney independently from the primary renal vessels
These occur in 10% of individuals and 98% arise from abdominal aorta. Most enter renal pelvis and pose little problem
When would an accessory renal artery cause a problem?
- aberrant renal arteries that enter the upper or lower poles of the kidney may pose problems
- inferior may cause obstruction of the ureter and may cause an intermittent or continuous obstruction to urinary drainage from the renal pelvis
What can renal agenesis lead to?
Potter’s syndrome
-not enough amniotic fluid
What causes renal fusion? What does it cause?
- prevents normal rotation
- abnormal blood supply - usually from middle sacral or common iliac arteries
- ectopic kidney - may also be crossed with/without fusion
- horseshoe kidney
What is a horseshoe kidney?
- most common
- 90% fused at lower pole
- usually found inferior to inferior mesenteric artery
What is Wilms’ tumor?
- cancer of the kidney that affects children under the age of 5
- caused by a mutation in the WT1 gene
How does the bladder form?
- the cloaca is divided by the urorectal septum
- the dorsal portion develops into the rectum and anal canal
- the ventral portion develops into the bladder and urogenital sinus, which will give rise to the bladder and lower urogenital tracts (prostatic and penile urethral in males, urethra and lower vagina in females)
How is the pelvic urethra related to the bladder in terms of development?
- ureteric buds open into bladder wall, while the mesonephric ducts open more inferiorly into the pelvic urethra (ductus deferens doesn’t open into the bladder)
- triangular region of the incorporated mesonephric duct incorporated in the bladder wall forms the trigone
What is a urachal fistula/cyst?
- bladder is continuous superiorly with allantois (which should collapse and become the urachus)
- the urachus may remain patent throughout its length (urachal fistula) or only at an end (urachal sinus)
- remnants if the urachal lumen may also give rise to urachal cysts -> usually present as abdominal masses
Outline when an embryo develops genital systems.
- weeks 1-6: embryo remains in an undifferentiated state
- week 7: phenotypic sexual differentiation begins
- week 12: male and female external genitalia can be recognized
- week 20: phenotypic differentiation complete
What triggers male development?
- SRY protein -> testes determining factor
- if not expressed, female path is followed
- female is the default pathway
What happens if TDF is not expressed?
-female path is followed
Outline the steps taken when the SRY gene is activated.
- differentiation of bipotential gonad into testis
- Sertoli cell differentiation
- Mullerian inhibitory substance
- regression of paramesonephric (Mullerian) ducts
Where do the genital ducts come from? Which one is male and which is female?
- both pairs are present during the indifferent stage
- male -> mesonephric duct
- female -> paramesonephric duct
How do the gonads develop?
- develops from three tissues: epithelium of intra embryonic coelom, intermediate mesoderm, and primordial germ cells
- primordial germ cells from mesoderm of yolk sac invade the dorsal mesentery and migrate to urogenital ridges
Primary sex cords are aggregates of ______________.
- supporting cells (hormone secreting cells)
- gonad now has an outer cortex and an inner medulla
What is the phallus, urogenital folds, and labiosacral swelling in male and female?
Male:
-penis, shaft of penis, scrotum
Female:
-clitoris, lab is minora, labia majora
What are some paramesonephric duct anomalies?
- uterus didelphys with double vagina (two everything)
- Uterus arcuatus (indentation of top of uterus)
- uterus bicornis (one vagina, two uteruses)
- uterus bicornis unicollis 1 rudimentary horn
- atresia of cervix
- atresia of vagina
What is Mullerian agenesis?
- failure of the paramesonephric ducts to develop
- results in missing uterine tubes, uterus and variable malformations of the upper portion of the vagina
- aka Mayer-Rokitansky-Kuster-Hauser syndrome (MRKH)
What is hypospadias?
Incomplete fusion if the urethral folds
- urethra opens onto the ventral aspect of the. Penis
- can result from inadequate androgen. Production or. Inadequate receptor sites for. DHT
What are the 4 types of hypospadias?
- Glandular
- Penile
- Penoscrotal
- Perineal
What is classic virilizing adrenal hyperplasia?
- female intersex
- females (XX) with severe forms of adrenal hyperplasia have ambiguous gentitalia at birth due to excess adrenal androgen production in utero
- ambiguous genitalia ranges from complete fusion of the labioscrotal folds and a phallic urethra to only clitoromegaly, partial fusion of labioscrotal folds, or both
- no ovarian abnormalities
What is androgen insensitivity syndrome?
- X linked disorder in which receptors remain unresponsive to androgens
- despite normal levels of testosterone the male fetus fails to masculinize
- external genitalia are feminine -> internally they possess non functioning nudes ended testes
- secondary sexual characteristics appear fir to estradiol from testosterone aromatization
- common to perform a gonadectomy and receive hormone therapy
What is a 5-a reductase deficiency?
- autosomal recessive condition resulting in the inability to convert testosterone to dihydrotestosterone (DHT)
- bc DHT is required for the normal masculinization of the external genitalia in utero, genetic males are born with ambiguous genitalia
- derivatives of mesonephric duct are normal
- often misdiagnosed as AIS
- third gender
What does the urinary system develop from? What forms the urogenital ridge?
- urinary and genital systems develop from intermediate mesoderm or trilaminar disc
- intermediate mesoderm separates from lateral and paraxial mesoderm during folding and forms urogenital ridge
