2. Development of renal system Flashcards
why are dev. of renal and repro. systems intimately linked
- both develop from UROGENITAL RIDGE of intermediate mesoderm along posterior wall of abdominal cavity
- excretory ducts of both systems initially enter common cavity - the CLOACA
describe the 3 stages of kidney system dev.
Organisation of intermediate mesoderm into 3 sequential systems - appear behind peritoneal cavity in cranial to caudal sequence:
- PRONEPHROS
- formation of nephrotomes (cervical region) that regress by end-week 4
- formation of pronephric duct - extends from cervical region to cloaca and drives dev. of next stage - MESONEPHROS
- dev. of nephron-like mesonephric tubules (upp thoracic to upper lumbar region) in week 4
- capable of producing urine but not of conserving water
- drained by mesonephric duct - METANEPHROS
- ureteric bud grows out of mesonephric duct… contacts metanephric blastema (region of undifferentiated intermediate mesoderm)…
- ureteric bud gives rise to collecting system
- blastema gives rise to excretory system - kidney nephrons
which structures arise from ureteric bud
Collecting system:
- ureter
- renal pelvis
- major and minor calyces
- collecting tubules
describe the localisation of the metanephric kidney - what is the consequence of this on vasculature
- first appears in pelvic region then undergoes caudal to cranial shift (true mov. + lengthening of embryo trunk)
- crosses arterial fork formed by embryo-placenta vessels
- during ascent, is vascularised by aortic branches which form and regress at continuously higher levels
which condition can early splitting of ureteric bud give rise to
- duplication of ureter (in rare cases, 1 ureter opens into bladder whilst other is ectopic - entering vagina, urethra or vestibule… incontinence due to lack of sphincter)
- duplication of renal pelvis
- complete renal duplication
what causes pelvic kidney and what is the effect of this
- failure to pass arterial fork during metanephric kidney ascent
- usually asymptomatic but can cause incontinence, UTIs or renovascular hypertension
what is a horseshoe kidney
- occurs if kidneys are pushed so close during metanephric ascent through arterial fork that lower poles fuse
- kidney usually dound at lower lumbar vertebrae as further ascent prevented by root of inferior mesenteric artery
what are accessory renal arteries and why are they of clinical significance
- common, derive from persistence of embryonic vessels from aorta that form during ascent of kidneys
- are terminal/end arteries that supply small parts of kidney, and as they are narrow, are at greater risk of getting blocked and causing avascular necrosis
when does the definitive kidney become functional and what is its role
- week 12
- recycling/production of amniotic fluid
what is renal agenesis and why does this occur
- absence of 1 (unilateral) or both (bilateral) kidneys
- due to failure of ureteric bud to induce metanephric blastema (genetic as well as environmental factors?)
what is the clinical significance of unilateral renal agenesis
- usually asymptomatic
- increased filtration can cause hypertrophy of remaining kidney over time… hypertension… renal failure
what is the clinical significance of bilateral renal agenesis
- causes abnormally low amniotic fluid volume as no urine produced - OLIGOHYDRAMNIOS
- results in POTTER SEQUENCE:
- PULMONARY HYPOPLASIA (amniotic fluid contributes to lung dev.)
- DEV. ABNORMALITIES (reduced space in amniotic sac)
- usually fatal within a few days after birth
what is the urogenital sinus - which structure does it form from and which structures does it give rise to
- UGS formed from division of CLOACA into UGS anteriorly and anal canal posteriorly by URORECTAL SEPTUM (week 4-7)
- upper part of UGS forms urinary bladder
- inferior part of UGS forms urethra
in which dev. abnormality might urine drain from umbilicus
URACHAL FISTULA
- Normally, bladder-part of UGS is initially continuous with allantois… lumen of allantois then obliterated… urachus (thick fibrous cord) remains to connect bladder apex to umbilicus… closes at birth to form median umbilical ligament
- Fistula is caused by persistence of intraembryonic portion of allantois, resulting in urine draining from umbilicus
what is a urorectal fistula and why can it arise
- connection between rectum and urethra caused by incomplete separation of hindgut from UGS by urorectal septum
