Embryology-Urinary Development Flashcards
What makes up the amniotic fluid?
Initially it comes from maternal blood and secretions from amniotic cells. At 5 months it contains fetal urine and later one meconium.
What is the purpose of the amniotic fluid?
Shock absorber and allows for fluid fetal movement.
What happens if amniotic fluid is insufficient?
Limited fetal growth and congenital defects (pulmonary hypoplasia)
Which embryonic layer is the kidney derived from?
Intermediate mesoderm. It forms the urogenital ridge.
What portion of the urogenital ridge gives rise to the urinary system?
Nephrogenic cord
What are the different kidneys formed from the nephrogenic cord?
In a cranial to caudal sequence, you first get formation of the pronephrous, then the mesonephros, and finally the metanephric kidney (definitive kidney).
How does formation of the pronephrous begin?
A series of epithelial buds come off of the intermediate mesoderm
What embryonic structure extends from the pronephrous to the cloaca (opening of the anus)?
The mesonephric duct (Wolffian ducts)
How does the mesonephric duct interact with the intermediate mesoderm?
It induces it to form mesonephric tubules. These tubules function as excretory units for the early fetus because there is no need to hyper concentrate the urine en utero.
What happens to the remnants of the mesonephric ducts?
They form structures in the male reproductive tract (vas deferents)
What initiates the formation of the permanent kidney?
The uteric bud comes off of the mesonephric duct and is surrounded by intermediate mesoderm. This develops to become the metanephric blastema.
What part of the intermediate mesoderm does the excretory system of the kidney form from? What about the collecting system?
Excretory = metanephric cap (mesoderm). Collecting = mesonephric duct (ureteric buds). The ureteric buds come into contact with the metanephric cap (blastema) to form the whole nephron.
What structures need each other in order to properly form the nephrons of the kidney?
RECIPROCAL INDUCTION. The metanephric blastema produces and secretes WT1. This causes the metanephric blastema to synthesize GDNF & HGF. These act on ureteric bud receptors and stimulate their release of BMP7 & FGF2, which maintain WT1 synthesis. Later on WNT peptides made by the ureteric bud cause the metanephric blastema to synthesize Pax2 (mesnchyme differentiation into epithelium) & WNT4 (tubule formation).
How do we get development of so many nephrons?
The ureteric bud continues to infiltrate and divide inside the metanephric blastema (cap).
What is the pathophysiology behind oligohydramnios?
Bilateral renal agenesis. In normal neonates, amniotic fluid is swallowed and recycled by the kidneys. In neonates without kidneys, amniotic fluid disappears as it is swallowed by the fetus and does not recycle.
What causes the kidney to ascend in the fetus? What makes them stop ascending?
Longitudinal fetal growth and straightening out of the fetus. Contact with the suprarenal glands causes them to stop ascending.
A patient comes to see you with excruciating flank pain. Ultrasound reveals a swollen kidney and CT scan reveals blockade of the left ureter by an accessory renal artery. Can you cut out the renal artery to relieve the patient?
No. Accessory renal arteries are end arteries and the tissue they supply will become ischemic.
What are accessory renal arteries remnants of?
Renal blood supply from the aorta as the kidney ascends. These normally (75% of the time) disintegrate.
What embryological origins does the adrenal gland have?
The cortex comes from the intermediate mesoderm and the medulla comes from the neural crest cells.
What is the diverticulum of the hind gut? What does it become?
Allantois. It becomes the urachus.
How do the urogenital sinus and anorectal canal form?
The urorectal septum divides the cloacal membrane into two separate compartments.
Where does the prostate form from?
The epithelium of the bladder
Why does the trigone feel different on a cadaver than the rest of the bladder?
Most of the bladder is formed from the endoderm. The trigone is a product of invagination of the bladder by mesonephric ducts, which are intermediate mesoderm. The epithelium of the bladder then grows and overlies the trigone.
What organ in the embryo is responsible for excreting waste products?
Placenta
If you see clear fluid coming from a newborn’s bellybutton, what embryological structure is it coming from?
Urachus
When do nephrons stop forming?
Birth
What is the pathogenesis behind a bifid ureter?
The ureteric bud branches prematurely before it meets the metanephric blastema.
What embryological defect may be responsible for a female who presents with urine coming out of the vaginal canal?
Ectopic ureter formation when the extra ureter does not open into the urinary bladder, but into the vagina.
What embryonic structure may have been absent on one side if a patient presents with only a single kidney?
The uteric bud or metanephric blastema. They need each other in order to have kidney development.
