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24 Cards in this Set
- Front
- Back
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Name some examples of substances that are secreted in the nephron.
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organic acids - PAH, salicylates
organic bases - morphine H+ K+ |
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What is the result of a filtered load that is greater than the excretion rate?
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net reabsorption
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At what point does glucose begin to appear in the urine?
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threshold - all glucose carriers in prox tubule filled
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Why does splay occur?
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1) low affinity of Na+ glucose cotransporter
2) nephron heterogeneity |
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What are three situations in which glucosuria would occur?
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1) diabetes mellitus
(increased plasma in blood) 2) pregnancy (increased GFR=increased filtered plasma) 3) renal glucosria (decreased affinity of glucose transporter) |
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Is PAH secretion a passive or active carrier-mediated process?
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active carrier mediated (cotransporter) in the proximal tubule (has a Tm)
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Filtration + secretion =
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excretion
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To measure RPF with PAH would you choose a plasma PAH concentration below Tm or above Tm?
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below Tm - need all PAH to be filtered or secreted
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Does urea have net reabsorption or secretion?
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net reabsorption (about 40% of filtered urea is excreted)
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What are the sites for urea reabsorption and secretion?
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reabsorption - proximal tubule, inner medullary collecting ducts
secretion - thin descending limb |
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Is ureaa reabsorbed/secreted via passive or active transport?
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passive mechanisms always DOWN its concentration gradient
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What are the two requirements for urea movement?
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1) conc gradient
2) nephrons must be permeable to urea |
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How much filtered urea is absorbed in the proximal tubule?
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50%
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How does more proximal water reabsorption affect the reabsorption of urea?
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the more proximal the water reabsorption, the more urea reabsorption takes place
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What happens to urea in the thin descending loop?
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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)
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What happens to urea in the thick ascending loop?
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it is impermeable to urea - but urea can become more concentrated if ADH is present and water is reabsorped
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What happens to urea at the inner meduallary collecting ducts?
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transporter for urea UT1 (facilitated diffusion) is turned on by ADH - urea is reabsorbed down conc gradient (40% is left to be excreted)
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What is urea recycling?
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urea otherwise excreted is reabsorbed into the interstitium (corticopappilary gradient)
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Why is this statement true: The higher the urine flow, the higher the urine excretion?
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Lower water absorption (with a faster flow rate) means less urea reabsorption and higher urea excretion
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For weak acids and weak bases, which form (of each) dominates at low pH?
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HA for weak acids
BH+ for weak bases |
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Do relative amounts of charged and uncharged species in urine vary with pH?
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yes
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Can charged, uncharged, or both species of weak acids and bases diffuse across cell membranes?
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uncharged species only
(at low pH for weak acid and at high pH for weak base) |
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At an acid urine pH, does clearance of salicylate increase or decrease?
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decreases because the weak acid is uncharged and can be reabsorbed across the membrane (less in tubular urine - less cleared)
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Does one want to acidize or alkalinize urine in an aspirin overdose?
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alkalinize so that more aspirin is cleared (charged form of weak acid so less can be reabsorbed across membrane
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