Embryology V - GU Systems Flashcards
Which of the 3 germ layers is the genitourinary system drive from?
Mesoderm
More specifically, the intermediate mesoderm
What structures do the kidneys develop from?
The intermediate mesoderm of the urogenital ridges
this occurs in a cranial to caudal fashion during weeks 4-10
What are the 3 progressive developmental stages of the kidney?
- Pronephros (1st kidney. Develops at cranial end of urogenital ridges. Never functions in humans)
- Mesonephros (2nd Kidney. Forms as pronephros regresses.)
- Metanephros (final kidney)
Function of the Mesonephros?
Filtration and Collection
Mesonephros develops the mesonephric duct which gives it the collecting function. The duct drains into the cloaca of the hindgut.
T or F: When the mesonephros regresses, the mesonephric duct is retained in both males and females.
False.
The mesonephric duct is retained in males and contributes to the formation of the male genital tract. It regresses in females
What is another name for the mesonephric duct?
Wolffian duct
*used interchangeably on Step 1
When does the Metanephros begin to form?
While the mesonephros is still functional, around the 4th to 5th week
From what two distinctive mesodermal structures does the metanephros develop from?
Ureteric bud and Metanephric blastema (mass)
What is the name of the newborn defect caused by the failure of the ureteric bud, or the metanephric blastema to form?
Renal Agenesis
This also includes the failure of these two structures to make good contact during development.
Defect is usually asymptomatic. The other kidney (if formed correctly) will compensate.
More common in males
Usually occurs on left side (not known why)
Which structure gives rise to the collecting system?
A. The Metanephric Blastema
or
B. The Ureteric Bud?
Ans: B, the Ureteric Bud
Name the order of structures in which urine flows through the collecting system starting from the nephron.
- Collecting tubules
- Minor calyces
- Major calyces
- Renal pelvis
- Ureter
Name the defect that occurs when two ureteric buds develop simultaneously, or when a single uremic bud splits into two distinct parts
Double Ureter
These defects are usually unilateral and asymptomatic
What is the difference between a double ureter defect and and ectopic ureter defect?
Ectopic ureter occurs when one ureter opens into the bladder as it should, while the other one opens abnormally in some ectopic position.
This is clinically important because it may lead to urinary incontinence (involuntarily pissing your pants)
Which structure form the nephron of the kidney?
The Metanephric mass (blastema)
What comprises the Nephron?
Proximal and distal convoluted tubes
Loop of Henle
Bowman’s Capsule
What is the name for the defect of renal development that results in one kidney being smaller that the other, but still architecturally normal with normal nephron density?
Unilateral hypoplastic kidney
The development of an extra kidney is called?
Supernumerary Kidney
Results from splitting of the metanephric blastema
Also clinically asymptomatic
In fetal poylcystic kidney disease, what structure fails to form normally? What happens instead?
Collecting ducts
The dilate and form fluid-filled cysts
This may be life threatening; Kidneys will not function leading to renal failure at birth
infants will not survive long unless dialysis occurs immediately. Renal transplant is an option
What is the most common cause of Bilateral renal agenesis (failure of both kidneys to form)?
Oligohydraminos
What usually accompanies bilateral renal agenesis
Potter sequence (pulmonary hypoplasia, limb defects, facial deformities)
What causes the ascent of the kidneys during development?
Dimunution (reduction in size) of the body curvature and differential growth of the lumbar and sacral regions
At which vertebrae do the kidneys ascend to?
T12-L3 (in the posterior abdominal wall)
What are the two positional defects associated with the kidneys?
- Pelvis (ectopic) Kidney - it remains in the pelvis close to the common iliac. Usually insignificant unless it gets twisted
- Horseshoe Kidney - The kidneys are pushed so close together during their passage through the atrial fork that they fuse together at their lower poles. Rare and asymptomatic
What separates the Cloaca of the hindgut?
The urorectal septum
What is the urorectal septum?
A dorsal growth of mesoderm that divides the cloaca into an anterior urogenital sinus and a posterior anorectal canal
What does the urogenital sinus form?
Bladder
Urethra
Prostate gland (males)
Lower vaginal canal (females and Hardie)
What structure(s) does the mesonephric duct ultimately give rise to?
The epididymis, vas deferens, and seminal vesicles
What is the anatomical relationship between the mesonephric duct and the ureter in the definitive adult structure?
The mesonephric duct loops superior to the ureter
What part of the urethra does the mesonephric duct drain into?
The prostatic part
What part of the urogenital ridge does the gonad develop from?
The medial aspect of the more central region
Primordial germ cells (PGCs) fully populate the developing gonads by what week?
The 6th week
What will become of the primary sex cords in males? in females?
In males, the cords hollow out, lengthen, and coil forming the seminiferous tubules (under this influence of testosterone)
In females, the cords will not elongate, but instead they will regress, breaking up into small segments that form the 1st generation of primordial follicles
What happens to the mesonephric duct and the paramesonephric duct in FEMALES
Mesonephric duct regresses
Paramesonephric remains and gives rise to female genital tract
What happens to the mesonephric duct and the paramesonephric duct in MALES
Paramesonephric duct regresses
Mesonephric duct remains and gives rise to the male genital tract
When does the indifferent gonad begin to transform into either a testis or an ovary?
In the 7th week
What triggers the transformation of the indifferent gonad into a testis?
Testis-determing factor (TDF)
-produced under the influence of the SRY gene on the Y chromosome
What are the two major cell lines that make up the testis?
Leydig and Sertoli cells
-TDF stimulates the development of these cell lines
What are the roles of Leydig cells in male gonadal development?
They produce and secrete testosterone
What are the roles of Sertoli cells in male gonadal development?
they produce and secrete Mullerian-inhibiting factor (MIF)
-MIF drives the regression of the paramesonephric (Mullerian) ducts in the male
What drives the development of male external genitalia?
Dihydroxytestosterone (DHT)
What is the name of the enzyme that converts testosterone to DHT?
5alpha-reductase 2
converts the testosterone made by Leydig cell into DHT
Low levels of DHT during development produce what in males?
Microgenitalia (small dick, small scrotum)
Low levels of MIF during development in males results in what?
Male intersexuality (Genetic male, with female characteristics)
Where are the PGCs storedin males by puberty?
Seminiferous tubules (which formed under the influence of testosterone)
What factors are involved withe differentiation of the female gonad?
None
-development of the ovary is the default sequence in the absence of the Y chromosomes and TDF
What stimulates the development of the paramesonephric duct in females?
Estrogen
-estrogen also drives the growth of the external genitalia (labia, clitoris, and lower vaginal canal)
What structure(s) does the paramesonephric give rise to in females?
The uterine tubes, uterus, cervix, and upper vaginal canal
From what structures does the vaginal canal develop from?
Upper vaginal canal = Paramesonephric duct (mesoderm)
Lower vaginal canal = urogenital sinus (endoderm)
What is a Gartner’s Cyst?
Hint: found in females
A small remnant of the mesonephric duct found near the vaginal canal
-clinically important if it get infected or inflamed
What is a bicornate uterus? How is it formed?
The most common defect in uterine development that results in a double-horned uterus with some degree of septation, and one single vaginal canal.
caused by the failure of the two paramesonephric ducts to fuse
When can the sex of a fetus be determined?
After the 12th week
after the external genitalia undergo differentiation
What are the 3 components of the indifferent genitalia?
- genital tubercle
- urogenital folds
- lateral genital swellings
What component of the indifferent genitalia forms the scrotum?
The two lateral genital swellings
-they come together and fuse in the midline
What component of the indifferent genitalia forms the glans of the penis, and part of the shaft of the penis?
Genital tubercle
What component of the indifferent genitalia forms the ventral shaft of the penis?
The two urogenital folds
- they come together and fuse in the ventral midline
- the fusion also encloses the proximal part of the penile urethra
What component of the indifferent genitalia forms the clitoris?
The genital tubercle
What component of the indifferent genitalia forms the labia minor?
the two urogenital folds
they do NOT fuse together
What component of the indifferent genitalia forms the labia major?
The two lateral genital swellings
they do NOT fuse at the midline
