sturge_weber
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a 75 yr old man with chronic bronchitis visits her physician for annual checkup... the foll. data re obtained
ph=7.39, pco2=55meq/l, hco3-=32meq/l
what is the major compensatory response to this patients acid base disorder?
a.decreased renal bicarbonate ion secretion
2. decreased renal hydrogen ion secretion
3. hyperventilation
4. hypoventilation
5. increased carbonic anhydrase activity
my doubt is between in choices a nad e, the ans in q bank is a, but why not e, as if we increase carbonic anyhydrase activity, more of h2co3 will form and it will break to form h20 and co2 and the co2 will be reabsorbed, and then combined with h2o to form h2co3 which will give hco3-
please explain
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| cyra
Moderator
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The patient has chronic bronchitis...a COPD...and so would have a respiratory acidosis...the labs given indicate there has been compensation...now the main compensation for a resp acidosis is renal...and that would be increased reabsorption of HCO3-.....or in other words as the ques states...decreased renal bicrab secretion...
i would not go for choice e/5 cos its not specific ..sure, the underlying mechanism at the cellular level for increased reabsorption of bicarb is increased carbonic anhydarse activity...but the choice doesn't state "where"...so i'd say choice "a"...
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| reet
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question itself asking MAJOR COMPENSATION response?????
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| dariush
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i think sturge_weber is right, the main mech. is CA induction which MAKES more NEW H2Co3 rather than preventing its excretion.
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| cyra
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I understand where you are coming from.....i thought that the renal response to respiratory acidosis (and even metabolic acidosis) is the following...
1.secretion of H+(forming an acid urine)
2.reabsorption of filtered bicarbonate(this in turn is a result of an excess of of H+ in the renal tubules causing a complete reabsorption of HCO3-...this tkaes place in the PCT)
3.production of "new" HCO3-...which is due to the additional H+ in the renal tubules combining with the urinary buffers...NH4+ and HPO4-)...this would mostly be in the DCT and the collecting ducts .
My point being...sure carbonic anhydrase is the underlying cellular "mechanism" but the questions asks for the "compensatory response"....
check this link out...its pretty good...http://www.anaesthesiamcq.com/AcidBaseBook/ab4_5.php
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| GMOB
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I agree with Cyra...
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