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24 Cards in this Set

  • Front
  • Back
Name some examples of substances that are secreted in the nephron.
organic acids - PAH, salicylates
organic bases - morphine
What is the result of a filtered load that is greater than the excretion rate?
net reabsorption
At what point does glucose begin to appear in the urine?
threshold - all glucose carriers in prox tubule filled
Why does splay occur?
1) low affinity of Na+ glucose cotransporter
2) nephron heterogeneity
What are three situations in which glucosuria would occur?
1) diabetes mellitus
(increased plasma in blood)
2) pregnancy
(increased GFR=increased filtered plasma)
3) renal glucosria
(decreased affinity of glucose transporter)
Is PAH secretion a passive or active carrier-mediated process?
active carrier mediated (cotransporter) in the proximal tubule (has a Tm)
Filtration + secretion =
To measure RPF with PAH would you choose a plasma PAH concentration below Tm or above Tm?
below Tm - need all PAH to be filtered or secreted
Does urea have net reabsorption or secretion?
net reabsorption (about 40% of filtered urea is excreted)
What are the sites for urea reabsorption and secretion?
reabsorption - proximal tubule, inner medullary collecting ducts

secretion - thin descending limb
Is ureaa reabsorbed/secreted via passive or active transport?
passive mechanisms always DOWN its concentration gradient
What are the two requirements for urea movement?
1) conc gradient
2) nephrons must be permeable to urea
How much filtered urea is absorbed in the proximal tubule?
How does more proximal water reabsorption affect the reabsorption of urea?
the more proximal the water reabsorption, the more urea reabsorption takes place
What happens to urea in the thin descending loop?
the thin descending loop is permeable to both water and urea, so urea is secreted down its conc gradient INTO nephron (110% of filtered load present)
What happens to urea in the thick ascending loop?
it is impermeable to urea - but urea can become more concentrated if ADH is present and water is reabsorped
What happens to urea at the inner meduallary collecting ducts?
transporter for urea UT1 (facilitated diffusion) is turned on by ADH - urea is reabsorbed down conc gradient (40% is left to be excreted)
What is urea recycling?
urea otherwise excreted is reabsorbed into the interstitium (corticopappilary gradient)
Why is this statement true: The higher the urine flow, the higher the urine excretion?
Lower water absorption (with a faster flow rate) means less urea reabsorption and higher urea excretion
For weak acids and weak bases, which form (of each) dominates at low pH?
HA for weak acids
BH+ for weak bases
Do relative amounts of charged and uncharged species in urine vary with pH?
Can charged, uncharged, or both species of weak acids and bases diffuse across cell membranes?
uncharged species only
(at low pH for weak acid and at high pH for weak base)
At an acid urine pH, does clearance of salicylate increase or decrease?
decreases because the weak acid is uncharged and can be reabsorbed across the membrane (less in tubular urine - less cleared)
Does one want to acidize or alkalinize urine in an aspirin overdose?
alkalinize so that more aspirin is cleared (charged form of weak acid so less can be reabsorbed across membrane