Primary Examination SAQs

Study notes for the ANZCA Primary Examination SAQs

Acid Base

with 2 comments

2010b(15)03a(9) Explain the role of haemoglobin as a buffer

2008a(11)95b(8) Outline the physiological consequences of hyperosmolar diabetic ketoacidosis

2007a(11)05a(15) Describe how the body handles a metabolic acidosis

2006b(15)98b(5) Explain how a metabolic acidosis develops in hypovolaemic shock. Describe consequences to the body

1999b(1)98a(6) How does a fall in temperature influence blood gas solubility & acid-base values?

 

 

 

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Written by primarysaqs

December 31, 2009 at 11:11 am

2 Responses

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  1. Hi Amanda,

    Thanks for creating and updating such an excellent resource.

    In the question “explain the role of haemoglobin as a buffer” you mention the Haldane effect in point 3 of Hb as a buffer. It is implied that 30% of the Haldane effect is due to maintenance of a concentration gradient of HCO3 between the inside and the outside of the cell.

    My understanding (from just reading the CO2 chapter in Nunn’s, the CEACCP on Acid Base physiology and the 2003 examiners report) was that this was related to the pKa of the histamine residues differing in the oxygenated and deoxygenated state (6.9 and 7.9 respectively). As they are acids, when the pKa approaches or exceeds physiological pH the residues will become more unionised (i.e. less dissociated from H+) and therefore be buffering greater quantities of H+. This you go onto mention in dot point 4, but don’t mention the Haldane effect here.
    I’m sure the resultant increase in available HCO3 behaves in the way described, but is not responsible for the Haldane effect as the notes suggest.

    Cheers

    Colin

    Colin

    October 16, 2016 at 1:05 pm


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