Renal Flashcards – First Aid for the USMLE STEP 1

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  • timeline of pronephros?
    week 4; then degenerates
  • function of mesonephros?
    functions as interim kidney for 1st trimester; later contributes to male genital system
  • timeline of metanephros?
    permanent; first appears in 5th week of gestation; nephrogenesis continues through 32-36 weeks of gestation
  • ureteric bud derived from what?
    caudal end of mesonephros
  • ureteric bud gives rise to what?
    "ureter, pelvises, calyces, and collecting duct"
  • timeline of ureteric bud?
    fully canalized by 10th week
  • function of metanephric mesenchyme?
    ureteric bud interacts with this tissue; interaction induces differentiation and formation of glomerulus through DCT
  • aberrant interaction between ureteric bud and metanephric mesenchyme may result in what?
    several congenital malformations of the kidney
  • timeline of ureteraopelvic junction?
    last to canalize
  • most common site of renal obstruction (hydronephrosis) in fetus?
    ureteropelvic junction
  • what happens in Potter's syndrome?
    "oligohydramnios --> compression of the fetus --> limb deformities, facial deformities, and pulmonary hypoplasia (cause of death) 'babies who can't Pee develop Potters'"
  • causes of Potters syndrome include what?
    "ARPKD, posterior urethral valves, bilateral renal agenesis"
  • what happens in horseshoe kidney?
    "inferior poles of both kidneys fuse as they ascend from pelvis during renal development, horseshoe kidneys get trapped under IMA and remain low in the abdomen"
  • kidney function in horseshoe kidney?
    normal
  • horseshoe kidney assoicated with what?
    Turner syndrome
  • multicystic dysplastic kidney is due to what?
    abnormal interaction between ureteric bud and metanephric mesenchyme --> nonfunctional kidney consisting of cysts and connective tissue
  • most common presentation of multicystic dysplastic kidney?
    unilateral generally asymptomatic with compensatory hypertrophy of contralateral kidney
  • multicystic dysplastic kidney often diagnosed how?
    prenatally via U/S
  • which kidney is taken during living donor transplantation?
    let bc it has longer renal vein
  • course of the ureters?
    pass under uterine artery and under ductus deferens (retroperitoneal)
  • what is the 60-40-20 rule of body weight?
    60% total body water 40% ICF 20% ECF
  • fraction of total body water that is ECF?
    1/3
  • fraction of total body water that is ICF?
    2/3
  • fraction of ECF that is plasma volume?
    1/4
  • fraction of ECF that is interstitial volume?
    3/4
  • plasma volume measured by what?
    radiolabeled albumin
  • ECF measured by what?
    inulin
  • osmolarity of body fluid?
    290
  • glomerular filtration barrier responsible for what?
    filtration of plasma according to size and net charge
  • glomerular filtration barrier composed of what?
    1. fenestrated capillary endothelium 2. fused basement membrane with heparan sulfate 3. epithelial layer composed of podocyte foot processes
  • function of capillary endothelium in glomerular filtration barrier?
    size barrier
  • function of fused basement membrane with heparan sulfate in glomerular filtration barrier?
    negative charge barrier
  • glomerular charge barrier is lost in what?
    nephrotic syndrome
  • loss of charge barrier in nephrotic syndrome results in what?
    albuminuria hypoproteinemia generalized edema hyperlipidemia
  • Cx=?
    clearance of X in Ml/min Cx=UxV/Px = volume of plasma from which the substance is completely cleared per unit time
  • Ux= ?
    urine concentration of X
  • Px =?
    plasma concentration of X
  • V in clearance calculations =?
    urine flow rate
  • Cx< GFR -->?
    net tubular reabsorption of X
  • Cx > GFR -->?
    net tubular secretion of X
  • Cx=GFR-->?
    no net secretion or reabasorption
  • what can be used to calculate GFR?
    inulin clearance
  • why can inulin clearance be used to calculate GFR?
    it is freely filtered and is neither reabsorbed nor secreted
  • "using inulin, GFR=?"
    Uinulin x V/ Pinulin= C inulin = Kf [(Pgc - Pbs)- (#gc- #gs)]
  • #bs normally equals what?
    0
  • what is an approximate measure of GFR?
    creatinine clearance
  • why isn't creatinine clearance an accurate measure of GFR?
    slightly overestimates GFR because creatinine is moderately secreted by renal tubule
  • what defines the stages of chronic kidney disease?
    incremental reductions in GFR
  • Normal GFR=?
    100 mL/min
  • ERPF can be estimated using what?
    PAH clearance because it is both filtered and actively secreted in the proximal tubule All PAH entering the kidney is excreted
  • ERPF= ?
    Upah x V/Ppah= Cpah
  • RBF=?
    RPF/(1-Hct)
  • difference between ERPF and true RPF?
    ERPF underestimates true RPF by ~10%
  • Filtration Fraction (FF)= ?
    GFR/RPF
  • normal FF=?
    20%
  • filtered load=?
    GFR x [Plasma]
  • effects of NSAIDs on renal filtration?
    inhibit prostaglandin dilation of afferent arteriole FF remains constant
  • effects of prostaglandins on renal filtration?
    "dilate afferent arteriole ((increase) RPF, (increase) GFR, so FF remains constant)"
  • effect of ATII on renal filtration?
    "Angiotensin II preferentially constricts efferent arteriole ((decrease)RPF, (increase)GFR, so FF increases)"
  • effect of ACE inhibitors on renal filtration?
    inhibit ATII constriction of efferent arteriole FF (decrease)
  • effects of afferent arteriole constriction on glomerular dynamics?
    RPF (decrease) GFR (decrease) FF (GFR/RPF) NC
  • effect of efferent arteriole contriction on glomerular dynamics?
    (decrease) RPF (increase) GFR (increase) FF
  • effect of (increase) plasma protein concentration on glomerular dynamics?
    RPF=NC GFR=(decrease) FF= (decrease)
  • effect of (decrease) plasma protein concentration on glomerular dynamics?
    RPF=NC GFR= (increase) FF= (increase)
  • effect of constriction of ureter on glomerular dynamics?
    RPF=NC GFR=(decrease) FF= (decrease)
  • excretion rate=?
    V x Ux
  • reabsorption = ?
    filtered - excreted
  • secretion= ?
    excreted - filtered
  • normal glucose clearance?
    glucose at normal plasma level is completely reabsorbed in proximal tubule by Na+/glucose cotransport
  • what happens to glucose clearance at glucose of 160?
    glucosuria begins (threshold)
  • what happens to glucose clearance at glucose=350?
    "all transporters are fully saturated, Tm"
  • glucosuria is an important clinical clue to what?
    DM
  • effect of pregnancy on glucose clearance?
    "normal pregnancy reduces reabsorption of glucose and amino acids in the proximal tubule, leading to glucosuria and aminoaciduria"
  • normal amino acid clearance?
    sodium-dependent trnasporters in the proximal tubule reabsorb amino acids
  • what is Hartnup's disease?
    deficiency of neutral amino acid (tryptophan) transporter; results in pellagra
  • which part of renal tubule contains brush border?
    early proximal tubule
  • early proximal tubule reabsorbs what?
    "all of the glucose and amino acids most of the HCO3-, Na+, Cl-, PO4, H2O"
  • tonicity of absorption taking place in early proximal tubule?
    isotonic absorption
  • early proximal tubule generates and secretes what?
    ammonia as a buffer for secreted H+
  • effect of PTH in early proximal tubule?
    inhibits Na+/PO4 cotransport--> PO4 excretion
  • effect of ATII in early proximal tubule?
    "stimulates Na+/H+ exchange--> (increase) Na+, H2O, HCO3- reabsorption (permitting contraction alkalosis)"
  • how much Na is reabsorbed in early proximal tubule?
    65-80%
  • Thin descending loop of Henle does what to water?
    passively reabsorbs water via medullary hypertonicity (impermeable to Na+)
  • which part of nephron is the concentrating segment?
    Thin descending loop of henle
  • Thin descending loop does what to urine?
    makes urine hypertonic
  • what is actively absorbed in thick ascending limb of loop of henle
    "actively reabsorbs Na+, K+, and Cl-"
  • thick ascending limb of loop of henle indirectly induces paracellular reabsorption of what?
    Mg++ and Ca++ through (+) lumen potential generated by K+ backleak
  • permeability of thick loop of henle to water?
    impermeable to H2O
  • TAL does what to urine concentration?
    makes urine less concentrated as it ascends
  • how much Na+ is reabsorbed in TAL?
    10-20%
  • early DCT actively reabsorbs what?
    "Na+, Cl-"
  • early DCT does what to tonicity of urine?
    makes urine hypotonic
  • effect of PTH at early DCT?
    (increase) Ca++/Na+ echange --> Ca++ reabsorption
  • how much Na+ reabsorbed at early DCT?
    5-10%
  • collecting tubules resbsorb what?
    Na+ in exchange for secreting K+ and H+ (regulated by aldosterone)
  • effect of aldosterone in collecting duct?
    acts on mineralocorticoid receptor --> insertion of Na+ channel on luminal side
  • effect of ADH on collecting duct?
    acts at V2 receptor --> insertion of aquaporin H2O channels on luminal side
  • how much Na+ reabsorbed in collecting duct?
    3-5%
  • drugs that act on PCT?
    carbonic anhydrase inhibitors
  • drugs that act on TAL?
    loop diuretics
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