Development and Pediatric Kidney

Question 1

Do kidneys develop in one place and in one stage?

Answer 1

NO! they develop in three different places in three different stages
*pronephros, mesonephros and metanephros

Question 2

All the three stages of nephritic devleopment hail from the same place called…?

Answer 2

• nephrogenic cord

* within the urogenital ridge

Question 3

The wolffian duct, which will become certain seminferous tubules in the male, really is the same thing as what developing kidney structure?

Answer 3

mesonephrict duct largely get’s “repurposed” into the wolffian duct in men
*in women, it just gets largely degenerated and resorbed

Question 4

The mullerian duct runs close to the developing kidney ducts. What is the other name for it?

Answer 4

paramesonephric duct

*grandmother structure of the uterine tubes and uterus

Question 5

Out of the mesonephric duct comes a diverticulum that will become the ureter and regions of the renal pelvis and major/minor calyces. What is that bud?

Answer 5

ureteric bud, which arises from the mesonephric duct

• remember that the sequence of ducts must be right or the kidney will not fully develop (agenesis)
• the ureteric bud is enveloped by the metanephric blastema, which will become most of the developed kidney

Question 6

What are the malpighian pyramids?

Answer 6

collection of early tubules which arise from the ureteric bud

• essentially run parallel to each other from medulla to cortex
• become the collecting ducts
• the epithelial cells around them will become the ureters, pelvis, calyces. thus the ureteric bud has the cells that make the DISTAL (not proximal) functional nephron parts

Question 7

Where do the proximal convoluted tubule and the loop of henle come from?

Answer 7

• the immediate previous step was the medulla-to-cortex growth of the collecting tubules. Once the collecting tubules reach the capsular region, they stop growing
• at the “tip” of these collecting tubules (cortical region) metanephric mesoderm cells (metanephric spheroid) are stimulated to differentiate
• the metanephric spheroid becomes the metanephric vesicle which will elongate and become the metanephric tubule that starts getting elongated and convoluted to form the rest of the nephron

Question 8

what’s up with the metanephric spheroid?

Answer 8

• becomes the metanephric vesicle which becomes the nephron from bowman’s capsule to the collecting duct
• these cells differentiate into epithelial tubes that elongate and convolute untill the tube meets the collecting duct on one end and the glomerulus on the other end

Question 9

How does the bowman’s capsule form?

Answer 9

The metanephric vesicle will form an elongating tube that “meets” other cells at both ends of the tube

1) one end meets the existing collecting tuble
2) another end meets the concurrently develping capillary bed in the cortical region (glomerulus)
* the end that meets the collecting tubule fuses and makes a contiguous tube but the other end that meets the vessel spreads out to encapsulate said capillary

Question 10

Where do the epithelial cells that make up the bowman’s capsule come from?

Answer 10

• the podocytes AND the parietal epithelium that makes up the bowman’s capsule come from the metanephric vesicle originally
• the metanephric vesicle is the descendent of the metanephric spheroid, a clump of cells that is induced to differentiate by the tips of the cortical collecting ducts
• the cells that immediately contact the capillary bed will become podocytes and the layer further out from the capillary becomes the parietal epithelium of the capsule
• remember the two ends of the tube meeting different structures

Question 11

What early structure gives rise to the urethra and bladder?

Answer 11

the urogenital sinus will eventually give rise to the bladder and urethra

Question 12

Describe the formation of the bladder and urethra

Answer 12

Urogenital sinus is endodermal and comes from the cloaca

• the urogenital sinus separates from the hindgut at 6-7 weeks and eventually it degenerates into a fibrous cord called the urachus
• the urachus will give rise to the bladder and urethra
• the tricky part to remember in males is that the prostatic urethra is formed by the mesonephric duct

Question 13

In females the bladder and urethra are all of endodermal origin. Is that true for males?

Answer 13

No, the prostatic urethra is mesonephric in origin so males have two different cell origins for their urethra

Question 14

What is hydronephrosis?

Answer 14

dilation of the renal pelvis by accumulated urine because of obstruction

Question 15

What’s up with a UPJ obstruction?

Answer 15

UPJ = ureteropelvic junction

• most common cause of pediatric hydronephrosis and more common in boys
• more common in left side than bilateral
• main problem is incomplete canalization of ureteric bud at 12 weeks gestation
• also can be due to local abnormality of smooth muscle fibers with increased fibrosis that impedes peristalsis

Question 16

What are the signs and symptoms of a UPJ obstruction?

Answer 16

ureteropelvic junction obstruction, often a developmnental abnormality, is a common cause of hydronephrosis in pediatric patients

• abdominal mass, pain, chronic/recurrent UTI
• diagnosed with antenatal ultrasonography
• treated by surgery and removal of the narrowing

Question 17

What’s up with ureteral duplication?

Answer 17

• most common renal abnormality (1% of population and 10% of children with UTIs)
• two ureters coming in from the same side
• propensity for VUR in lower one and obstruction in the upper one
• look for this in can’t-potty-train kids or continuous drip incontinence (could indicate an ectopic ureter that doesn’t go into the bladder)

Question 18

When you see UPJO what else do you look for?

Answer 18

other congenital abnormalities (this is one of a constellation of associated ones)
*also look for ipsilateral reflux

Question 19

What is a ureterocele?

Answer 19

cystic dilatation of the terminal intravesical ureter

• portion of the ureter that meets the bladder and fuses
• ectopic ureterocele = bladder neck or urethra location
• can cause obstruction or reflux depending on orientation

Question 20

ureteroceles are often components of what other developmental abnormality?

Answer 20

ureteral duplication (two ureters approaching from the same side)
*the upper pole is more often affected than the bottom pole

Question 21

If the urachus does not fully involute, what might result?

Answer 21

The urachus is the fibrous cord that the allontois eventually becomes. This is the marking of where the bladder and urethra are to develop from the urogenital sinus

• a urachal anomaly can connect the umbilicus to the bladder, causing pain on urination by pulling in on the umbilicus
• 30% of the time a cyst forms and causes a painful midline mass
• can sometimes be connected as a fistula and can drain clear or purulent urine at umbilicus

Question 22

What is the normal clinical presentation of a urachal remnant?

Answer 22

usually clear fluid accumulating in the umbilicus with micturation

• local irritation may cause a polyp
• remember the fistula isn’t always there so it could also just be the pain with micturation

Question 23

What is megalocystis?

Answer 23

AKA - megacystis

*chronic abnormal distension of the baldder by urine due to bladder outlet obstruction

Question 24

What’s up with a posterior urethral valve?

Answer 24

• obstructing membrane in posterior male urethra
• due to abnormal insertion of mesonephric duct on the cloaca prior to its dividing into urogenital sinus and anorectal canal
• messes with development of ALL upstream structures due to increased pressure

Question 25

Are posterior urethral valves common?

Answer 25

Meh. as far as these things go yes.

• 1/5000 male births
• most common male specific outlet obstruction
• diagnosed prenatally or with anuria and bladder distention

Question 26

What is it called when there is an extra/abnormal orifice on the ventral surface of the penis?

Answer 26

Hypospadias

*abnormal fusion of urogenital folds from androgen insufficiency

Question 27

What three conditions follow from improper folding and fusion of urogenital folds?

Answer 27

Hypospadia (hole on ventral penis), epispadia (hole on dorsal penis), extrophy (abdominal wall isn’t there exposing bladder mucosa)

Question 28

What’s up with oligohydramnios?

Answer 28

decreased amount of amniotic fluid because of the fetus’ inability to excrete urine

• sign of fetal urinary tract obstruction OR agenesis
• results in lung hypoplasia because of decreased developmnet

Question 29

Potter’s facies refers to what?

Answer 29

In situations of oligohydamnios the baby can have a flattened nose, large, flattened ears and infraorbital skin folds

Question 30

What is meant by “prune belly”?

Answer 30

Eagle Barrett syndrome

*atrophy of anterior abd. muscles because of megalocystis