Renal Embryology Flashcards
What are some characteristics of the intermediate mesoderm?
- Located in the trunk, lateral to each somite, segments into cylindrical structures
- produces the urinary system first & parts of genital
what is the urogenital ridge?
longitudinal band of mesoderm that forms on each side of the dorsal aorta; a portion will form the nephrogenic cord
What does the nephrogenic cord give rise to?
nephric structures: pronephros (rudimentary), mesonephros (functions briefly during early fetal life), metanephros (permanent kidneys)
Why are the pronephros important?
- because they initiate the cascade leading to formation of definitive kidney
- bilateral transitory structures, appear early in 4th week in cervical region, run caudally and open into cloaca, degenerate by 25 days, but ducts persist
What role do the mesonephros play in kidney development?
- appear late 4th week, caudal to pronephros
- include mesonephric ducts, develop first, and tubules that are induced from surrounding intermediate mesoderm
What do mesonephric tubules form?
renal corpuscles:
- Medial end of the tubules is a cup-shaped, glomerular capsule
- Wraps around a glomerulus (knot of capillaries)
-function as interim kidneys from 6-10 weeks, producing some urine
The caudal end of each mesonephric duct induces the formation of what structure?
-the ureteric bud
What is the metanephros comprised of?
- Metanephros =
1) Ureteric bud = outgrowth of mesonephric duct
2) Metanephric blastema = from nephrogenic cord - forms definitive kidney by 9th-10th week
- have excretory and collecting portion
Explain the formation of the ureteric bud and collecting system?
-Ureteric bud elongates & penetrates the blastema, to form the renal pelvis
-Stalk of ureteric bud becomes the ureter
-Cranial part of the bud branches → collecting tubules
1st generations (4) of tubules enlarge → major calices
2nd generations (4) → minor calices
Walk through nephron development:
1) Arched collecting tubule induces cells of
metanephrogenic blastema to form metanephric
vesicles
2) Vesicle will elongate to form metanephric tubules
3) Proximal end will form glomerular capsule, is invaded
by glomeruli
4) Other end of the tubule lengthens & differentiates →
→PCT, DCT, & nephron loop
5) Each DCT contacts an arched collecting tubule → now
connectedLO 4, 6, 7
Explain the vasculature and ascent of the kidneys
-lie within pelvis, gradually ascend into abdomen
-hilum medially rotates 90 degrees, adult position by 9th
week & in contact with suprarenal glands
-receive blood from closest vessels, first from common
iliacs, later definitively from renal arteries off abdominal
aorta
What are some accessory renal vessels?
-multiple renal arteries (2-4) are found in ~25% of adult kidneys, can obstruct ureter and lead to hydronephrosis
What are some embryological renal abnormalities?
-unilateral renal agenesis
-bilateral renal agenesis (nonviable)
-incomplete & complete ureter duplications
-horseshoe kidney, fusion of inferior poles to form
isthmus, typically asymptomatic, more inferior as IMA prevents ascent
What are some characteristics of cystic kidney disease?
-polycystic - autosomal recessive PKHD1 mut.; cysts in
both kidneys, renal insufficiency
-multicystic - many cysts of varying size, one kidney
affected, no cortical parenchyma
Why is the urogenital sinus critical for bladder and urethral development?
- Vesical part: forms most of the urinary bladder
- Pelvic part: forms neck of bladder; prostatic urethra
(m) & urethra (f) - Phallic part: forms spongy urethra (m) & lining of
vaginal vestibule (f)
How do the kidneys connect to the bladder?
-Between 4-6 weeks, the mesonephric duct is
incorporated into the posterior wall of the bladder
-Ureteric bud is also attached, which will connect the
openings of the ureteric buds into the bladder wall
-Openings of the mesonephric duct are carried inferiorly
to the pelvic urethra
-Forms the trigone, triangular region of the mesonephric
& ureteric ducts blending into posterior bladder
How does the bladder develop?
-mainly from the vesicle part of the urogenital sinus;
continuous with allantois
Epithelium= endoderm (urogenital sinus)
Submucosa & muscularis= splanchnic mesoderm
Trigone = intermediate mesoderm (mesonephric ducts)
What are some congenital anomalies of the bladder?
-exstrophy of the bladder - defective closure of
abdominal wall
-epispadias - urethral opening on dorsal side rather than
ventral
What urachal anomalies can arise during fetal development?
Urachal cysts: remnants of the epithelial lining of the urachus that can become infected & enlarged
Urachal sinus: end of the urachus remains open into the bladder (inferior region) or umbilicus (superior region)
Urachal fistula: entire urachus remains patent & allows urine to escape from umbilical orifice
Review the suprarenal gland.
Cortex:
•Zona glomerulosa: produces mineralocorticoids (regulate electrolytes)
•Zona fasciculata: produces glucocorticoids (regulate blood glucose levels, lipid metabolism)
•Zona reticularis: produces sex hormones, estrogen-& testosterone-related hormones (protein synthesis in sex cells)
Medulla: consists of chromaffin cells that secrete NE &Epi
How does the suprarenal gland develop?
1) 5th week, coelomic epithelium delaminates & enters
surrounding mesoderm → fetal cortical cells
2) Neural crest cells migrate into the medulla Will
differentiate into chromaffin cells Postganglionic
sympathetic neurons (Epi/NE)
3) Fetal cortex regresses (2ndmonth PN) Definitive cortical
cells reorganize: zona glomerulosa, zona fasciculata, &
zona reticularis (adult)
*clinical note: Fetal cortex will secrete dehydroepiandrosterone(DHEA) Converted by the placenta toestradiol
Essential for maintaining pregnancy
Also secretes ACTH & glucocorticoids
