10/9 Embryology of the Urinary Tract Flashcards
What are the three stages of Kidney Development?
Pronephros; Mesonephros; Metanephros
what is the funcitonal importance of the first stage of kidney development
Pronephros: Non-functional in humans, required for formation of subsequent kidneys; fuses with the cloaca
what is the functional importance of the second stage of kidney development
Mesonephros (middle kidney); Nephrons induced by the nephric duct; transient function; develop cranial to caudal sequence; 30-40 nephrons
what is the functional importance of the third stage of kidney development
Metanephros form the difinitive kidney.
what is a nephron
The combined structures of the Capillary to the glomerulus of the bowman’s capsule to the proximal convoluted tubule to the loop of Henle to the distal convoluted tubule to the stroma.
where do nephrons form
They first form in the mesonephros from the nephric duct that was initiated by the pronephros. they then form in the metanephros near the cloaca (bottom of gut tube).
what is the structural importance of nephrons
They are the Excretory component of the kidney – they filter the filtrate, then concentrate the urine and send it to the collecting component.
describe the formation of nephrons
form from the metanephric blastema (the outside developing tissue of the kidney).
Reciprocol induction with ureteric bud. Bud provides signals: FGF2/BMP7/Wnts. Mesenchyme respond and maintain with: WT1/WNT4/Pax2.
mesenchyme to epithelial transformation form renal vesicles that form bowman’s capsule.
how does the metanephric kidney change position during development.
it ascends from the cloacal neighborhood, to the mid-gut neighborhood and rotates 90 degrees to face medially now supplied by higher arteries.
what abnormalities develop due to the change in position of the kidneys during development
- persistance of the embryonic vessels from ascent -> vessel abnormalities.
- pelvic kidney (fails to ascend, located near common iliac)
- horseshoe kidney (due to fusion of caudal poles, ascent blocked by the inferior mesneteric; malrotated but functional)
how does the bladder develop from the urogenital sinus
originally the mesonephric duct empties into the cloacal.
urorectal septum descends like a curtain
urorectal folds swing in from the sides
divides the cloaca into bladder and rectum
what event is perturbed in the formation of urachal abnormalities
the allantois (fetal drainage of urine out the umbelical) involutes to form the urachus. this involuting should form the median umbilical ligament. but if it doesn’t then get urachal abnormalities
what are some common urachal abnormalities
- urachal fistula (urine leak from belly button)
- urachal cyst (cyst in the middle of the median umbilical ligament
- urachal sinus (opening from the belly b. to the median umbilical ligament.
describe the dual origin of the adrenal gland
- fetal mesothelium near the dorsal mesentery form the fetal cortex that becomes the Z. Fasciculata.
- Neural crest cells migrate in to form the chromaffin cells of the medulla.
- adult cortex formed of second wave of mesodermal cells that encapsulate and mature fully at puberty!
- runs into the kidney as it ascends!
what is the embrionic origin of the urinary system
intermediate mesoderm
Describe the initial functional kidney in an embrio
Mesonephric nephrons form from mesenchymal cell clusters that form vesicles that elongate to form tubules that connect to the nephric duct and form glomerulus with the aorta. Short tubes, urine is dilute.
what adult structures does the mesonephros contribute to?
in males only they form vas (ductus) deferens and efferent ductules of testis. Need testosterone for this to occur.
what are the two functional components of the metanephros?
Collecting component - ureteric bud
Excretory components: capillary -> glomerulus -> Bowman’s capsule -> proximal convolluted tubule -> loop of Henle -> Distal convoluted tubule -> Stroma.
Components of the Renal corpuscle
Capillary;
Glomerulus
Bowman’s capsule
describe formation of the collecting component
derives form the ureteric bud.
Branches to become the collecting tubule; minor and major calyces; renal pelvis; and ureter..
UB sprout from nephric duct, invade mesenchyme ->Dilate ->Renal Pelvis->1st division->major calyces->few branches fuse->minor calyces->5th gen branch->renal pyramids.
GDNF and HGF from blastema bind to RET and MET on UB, stimulates growth and branching.
what if no Wnt-4 in kidney development?
glomerular development arrests at the vesicle stage! don’t get real kidneys!
describe the tissue origin of the excretory component or the Nephron
Capillaries that produce the glomerulus
Metanephric mesoderm that produce: bowman’s capsule; henle’s loop; and distal convoluted tubule.
3 broad catagories of renal anomalies
agenesis ->the kidney doesn’t form
hypoplasia -> doesn’t form enough
dysplasia -> abnormal formation
severe cases of renal dysplasia and angenesis
potter sequences
what causes potter sequence?
oligohydramios (decreased amniotic fuid volume) resulting in flattened face, club feet and other ageneis and abnormalities!
Describe the insertion of the ureter into the bladder wall from starting out as a bud off of the nephric duct!
the nephric duct inserts into the bladder wall and swings up in a j shape to fuse into the wall and create the tigone (triangle of tissue from the nephric duct) on the back bottom of the bladder. -> ureter is brought down into up the back of the bladder -> now above the duct.
if you have a double ureter form, where would the duct be locate?
caudal to them
