Renal Flashcards
Prosnephros
Week 4, then degenerates
Mesonephros
- Functions as interim kidney for 1st trimester
- Later contributes to male genital system
Metanephros
- Permanent
- First appears in 5th week of gestation
- Nephrogenesis continues through 32-36 weeks of gestation
Ureteric bud
- Derived from caudal end of mesonephric duct
- Gives rise to ureter, pelvises, calyces, collecting ducts
- Fully canalized by 10th week
Metanephric mesenchyme/ blastema
- Ureteric bud interacts with this tissue
- Interaction induces differentiation and formation of glomerulus through to distal convoluted tubule (DCT)
- Aberrant interaction between these 2 tissues may result in several congenital malformations of the kidney
Uteropelvic junction
- Last to canalize
- Most common site of obstruction in fetus (hydronephrosis)
Horseshoe kidney associated with
- Hydronephrosis (eg uteropelvic junction obstruction)
- Renal stones
- Infection
- Chromosomal aneuploidy syndromes (eg Turner syndrome, trisomies 13, 18, 21)
- Renal cancer (rarely)
Compare unilateral renal agenesis and multicystic dysplastic kidney
Unilateral renal agenesis: ureteric bud fails to DEVELOP and induce differentiation of metanephric mesenchyme → complete absence of kidney and ureters; often diagnosed prenatally via ultrasound
Multicystic dysplastic kidney: ureteric bud fails to induce differentiation of metanephric mesenchyme → nonfunctional kidney consisting of cysts and connective tissue; often diagnosed prenatally via ultrasound
Duplex collecting system
- Bifurcation of ureteric bud before it enters the metanephric blastema creates a Y shaped bifid ureter
- Duplex collecting system can alternatively occur through ureteric buds reaching and interacting with metanephric blastema
- Strongly associated with vesicoureteral reflux and/or ureteral obstruction, ↑ risk for UTIs
Renal blood flow
Renal a. → segmental a. → interlobar a. → arcuate a. → interlobular a. → afferent arteriole → glomerulus → efferent arteriole → vasa recta/ peritubular capillaries → venous outflow
How to measure plasma volume
Radiolabeling albumin
How to measure extracellular volume
Inulin or mannitol
Filtration by fenestrated capillary endothelium
Size barrier
Filtration by fused basement membrane with heparan sulfate
Negative charge and size barrier
Filtration by epithelial layer consisting of podocyte foot processes
Negative charge barrier
What value can be used to calculate GFR
Inulin clearance, as it is freely filtered and is neither reabsorbed nor secreted.
Creatinine clearance is an approximate measure of GFR. Slightly overestimates GFR because creatinine is moderately secreted by renal tubules.
What value can be used to calculate effective renal plasma flow (eRPF)
Para-aminohippuric acid (PAH) clearance because between filtration and secretion there is nearly 100% excretion of all PAH that enters the kidney. eRPF underestimates true renal plasma flow (RPF) slightly.
Glucose clearance in a normal pregnancy
Normal pregnancy may decrease ability of PCT to reabsorb glucose and amino acids → glucosuria and aminoaciduria
Early PCT physiology
- Contains brush border
- Reabsorbs ALL glucose and AAs and MOST HCO3-, Na+, Cl-, PO43-, K+, H2O, and uric acid
- Isotonic absorption
- Generates and secretes NH3, which acts as a buffer for secreted H+
- PTH: inhibits Na+/PO43- cotransport → PO43- excretion
- ATII: stimulates Na+/H+ exchange → ↑ Na+, H2O, and HCO3- reabsorption (permitting contraction alkalosis)
- 65-80% Na+ absorbed
Thin descending loop of Henle physiology
- Passively reabsorbs H2O via medullary hypertonicity (impermeable to Na+)
- Concentrating segment
- Makes urine hypertonic
Thick ascending loop of Henle physiology
- Reabsorbs Na+, K+ and Cl-
- Indirectly induces paracellular reabsorption of Mg2+ and Ca2+ through + lumen potential generated by K+ backleak
- Impermeable to H2O
- Makes urine less concentrated as it ascends
- 10-20% Na+ reabsorbed
Early distal convoluted tubule physiology
- Reabsorbs Na+, Cl-
- Makes urine fully dilute (hypotonic)
- PTH: ↑ Ca2+/Na+ exchange → Ca2+ reabsorption
- 5-10% Na+ reabsorbed
Collecting tubule physiology
- Reabsorbs Na+ in exchange for secreting K+ and H+ (regulated by aldosterone)
- Aldosterone: acts on mineralocorticoid receptor → mRNA → protein synthesis
- Aldosterone and principal cells: ↑ apical K+ conduction, ↑ Na+/K+ pump, ↑ epithelial Na+ channel activity (ENaC) → lumen negativitiy → K+ secretion
- Aldosterone and α intercalated cells: lumen negativity → H+ ATPase activity → ↑ H+ secretion → ↑ HCO3-/Cl- exchanger activity
- ADH: acts at V2 receptor → insertion of aquaporin H2O channels on apical side
- 3-5% Na+ reabsorbed
How much Na+ is reabsorbed at various parts of the nephron
- PCT → 65-80%
- Thick ascending loop of Henle → 10-20%
- Early DCT → 5-10%
- Collecting tubule → 3-5%