Renal Embryology B&B

Question 1

from which embryonic layer are the kidneys derived, and what are the 3 stages of embryonic renal development

Answer 1

intermediate mesoderm - 3 embryonic renal structures form in utero, first 2 degenerate:

1. pronephros: week 4
2. mesonephros: 1st trimester, contributes to vas deferens in males
3. metanephros: appears 5th week, permanent kidney

Question 2

what do the embryonic ureteric bud and metanephric mesenchyme become, respectively?

Answer 2

ureteric bud: outgrowth of mesonephric (Wolffian) duct, becomes ureter/pelvis/calyxes/collecting ducts

metanephric mesenchyme (aka metanephric blastema): interacts with ureteric bud to form glomerulus to distal tubule

*aberrant interaction between ureteric bud and metanephric mesenchyme = kidney malformation!

Question 3

Wilms’ Tumor

Answer 3

proliferation of metanephric blastema/mesenchyme - embryonic glomerular structure

associated with mutations of WT1 - expressed in metanephric blastema

most common renal malignancy in young children

Question 4

most common renal malignancy in young children, caused by proliferation of metanephric blastema

Answer 4

Wilms’ Tumor - associated with mutations in WT1

Question 5

what causes renal agenesis and what is the physiologic consequence of this?

Answer 5

ureteric bud fails to develop, therefore fails to signal to mesenchyme

if single kidney, other kidney compensates —> hypertrophy, hyperfiltration, risk of focal segmental glomerular sclerosis, risk of renal failure (decades later)

if both kidneys —> oligohydramnios, Potter’s syndrome

Question 6

multicystic dysplastic kidney

Answer 6

abnormal ureteric bud-mesenchyme interaction in utero —> kidney replaced with cysts

no/little functioning renal tissue

Question 7

what is the consequence of ureteropelvic junction (UPJ) obstruction?

Answer 7

ureteropelvic junction is last renal connection to form in embyro

obstruction —> narrowing at proximal ureter at junction

—> hydronephrosis, poor urinary flow —> kidney stones/UTIs

*common cause of single kidney obstruction, often detected in utero, can be treated with surgery after birth

Question 8

describe what occurs in a duplex collecting system?

Answer 8

duplicated ureter due to 2 ureteric buds or a bifurcated ureteric bud —> upper and lower kidneys form

—> poor urine flow, hydronephrosis, UTIs, vesicoureteral reflux

Question 9

primary vs secondary vesicoureteral reflux

Answer 9

backward urine flow from bladder to kidneys, causes recurrent UTIs

primary: abnormal closure of ureterovesical junction (UVJ), associated with duplex ureters, occurs in children

secondary: caused by high bladder pressure, seen with posterior urethral valves

Question 10

Patient is a 2yo M presenting with vesicoureteral reflux, with a history of recurrent UTIs. The mother did not receive prenatal care due to limited healthcare access. What is likely the cause of these symptoms?

Answer 10

likely primary vesicoureteral reflux (abnormal closure of ureterovesicular junction) in association with duplex ureters (2 ureteric buds or bifurcation of ureteric bud in utero)

Question 11

what is Potter’s Syndrome/Sequence and how/when does it present?

Answer 11

due to absent/low amniotic fluid (fetal urine) —> loss of fetal cushioning to external forces and compression of fetus

—> limb deformities, flat face, pulmonary hypoplasia, often fatal

1st trimester (1-12w): rare
2nd trimester (13-27): most common, due to decreased formation of fetal urine
3rd trimester (28+w): due to rupture of membranes

Question 12

how can bilateral renal agenesis cause Potter’s Syndrome?

Answer 12

Potter’s: absent/low amniotic fluid —> loss of fetal cushioning/ compression of fetus

bilateral renal agenesis: ureteric buds fail to develop —> amniotic fluid cannot be produced

Question 13

how can posterior urethral valves cause Potter’s Syndrome?

Answer 13

Potter’s: absent/low amniotic fluid (fetal urine) —> loss of fetal cushioning/ compression of fetus

posterior urethral valves: in males, valve tissue obstructs bladder outflow (both kidneys effected), dilated bladder/kidneys on ultrasound

Question 14

what is the inheritance pattern of polycystic kidney disease and how can it cause Potter’s Syndrome?

Answer 14

Potter’s: absent/low amniotic fluid —> loss of fetal cushioning/ compression of fetus

polycystic kidney disease: juvenile form of cystic kidney disease (AR), both kidneys effected —> if severe, cysts can cause oligohydramnios

if less severe, can cause renal failure and HTN in childhood

Question 15

which 2 genetic conditions is horseshoe kidney associated with?

Answer 15

horseshoe kidney: inferior poles fuse, kidney cannot ascend pelvis (trapped by inferior mesenteric artery)

associated with 1. Turner Syndrome and 2. Down Syndrome

Question 16

what causes a horseshoe kidney to develop?

Answer 16

inferior poles fuse both kidneys into one —> kidney cannot ascend pelvis because it is trapped by the inferior mesenteric artery (stays in retroperitoneum)

most patients are asymptomatic, but associated with vesicoureteral reflux

Question 17

what does the urachus become after birth?

Answer 17

urachus: connects dome of bladder to the umbilicus, obliterated at birth to become medial umbilical ligament

if failed/incomplete obliteration —> urine can leak and cause infections, cyst/sinus/diverticulum can form

Question 18

Patient is a 38yo F presenting with painless hematuria. Imaging reveals a tumor at the dome of the bladder, and pathology confirms adenocarcinoma. Where did this tumor come from?

Answer 18

remnant of urachal cause formation of adenocarcinoma of bladder …

urachus: connects dome of bladder to the umbilicus, obliterated at birth to become medial umbilical ligament

if failed/incomplete obliteration —> urine can leak and cause infections, cyst/sinus/diverticulum can form

Question 19

how does the intermediate mesoderm differentiate/develop to become the kidneys?

Answer 19

intermediate mesoderm differentiates into urogenital ridge which runs vertically along the length of the posterior body wall…

a. pelvic/sacral cells form metanephros, which becomes nephrons

b. ureteric bud sprouts off the mesonephric duct and becomes collecting ducts, calyces, and ureters

nephron + collecting system = uriniferous tubule

Question 20

from what embryonic structure does the urinary bladder and urethra develop?

Answer 20

the urinary bladder and urethra develop from the embryonic urogenital sinus

Question 21

what does the embryonic cloaca become?

Answer 21

cloaca: caudal end of the embryo’s endoderm-lined gut tube

mesoderm wedge called urorectal septum divides cloaca into anterior urogenital sinus and posterior anorectal canal

superior part of urogenital sinus becomes the urinary bladder, and inferior parts becomes urethra

Question 22

how does a urachal fistula form and what is the consequence of this?

Answer 22

urachus/allantois is continuous with the superior part of the urogenital sinus (which becomes urinary bladder) and it courses into the umbilical cord

if urachus is not closed after birth, patent urachal fistula forms and urine can leak at the umbilicus

Question 23

what is bladder exstrophy and how does it occur?

Answer 23

bladder exstrophy: bladder forms outside of the body wall, due to defective anterior body wall fusion in the pelvic region during lateral body wall folding

Question 24

what embryonic structure forms the trigone in the bladder?

Answer 24

trigone: part of urinary bladder where mesonephric ducts fuse into the wall