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NBME 22 Answers

nbme22/Block 3/Question#6 (37.5 difficulty score)
A 50-year-old man is admitted to the hospital ...
Intracellular [Na+]: increased;
Intracellular [K+]: decreased;
Intracellular [Ca2+]: increased


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hope this image help to understand it, the pumps don't work because lack of ATP

 +2  upvote downvote
submitted by oznefu(16),
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tBu if rethe aer ndserceai aaccird esymezn ni eht oobdl aiigtdnnic llce dtahe dan mmeebran aem,adg ’twuolnd eht eiurtallnarcl etolrlsyctee eb low nscie hyte are edlresea iton eht ?dloob

lord_voss  troponin = irreversible injury and membrane damage -> high extracellular concentration of Na+ and Ca++ causes both to move into cell through damaged membrane and high intracellular K+ leaves the cell +11  
rogeliogs  Question is asking about the changes in the myocardiocytes and my second interpretation was that they are asking the changes before they "rupture" and liberate their content in the blood producing increase enzymes in the patient. Therefore because is a ischemic process = reduction of O2 = low ATP = impairment of Na/K ATPase = increase Na-decrease K intracellular = block Ca/Na exchanger = increase Ca intracellular. the same effect as digoxin +3  
allodynia  What will happen to Na and ca conccentration when there is an irreversible injury? +  
baja_blast  @allodynia Pathoma pg. 4 has a really good summary of this. In short, Na+ and Ca2+ both increase intracellularly in an irreversible injury. +  

In cellular ischemia, the Na+/K+ ATPase pump stops working due to decreased ATP levels. Consequently, sodium is not pumped out and potassium is not pumped into the cell, leading to an accumulation of sodium in the cell and potassium outside the cell. Furthermore, the sarcoplasmic reticulum Ca-ATPase pump fails, which leads to an increase in calcium in the cell.

Bottom line, ischemic tissue: there is a buildup of sodium and calcium in the cell.

 +1  upvote downvote
submitted by delamj(4),

I thought this was a pretty good summary from wikipedia.

Steps 1-4 explain the question:

  1. Lack of oxygen causes the [cardiomyocyte's] normal process for making ATP for energy to fail.
  2. The cell switches to anaerobic metabolism, producing lactic acid.
  3. ATP-reliant ion transport pumps fail, causing the cell to become depolarized, allowing ions, including calcium (Ca2+), to flow into the cell.
  4. The ion pumps can no longer transport calcium out of the cell, and intracellular calcium levels get too high.

Another way to think about this is just that decreased O2 leads to dysfunction of the Na+/K+ ATPase as others have mentioned.

This is pretty much identical to the mechanism of digoxin, which blocks the Na/K ATPase and calcium accumulates in the cell because it cant be exchanged for extracellular Na+ (which is not intracellular due to defective Na/K ATPase)

 -3  upvote downvote
submitted by sbryant6(128),
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If uoy know hte AMO fo nxgidoi oyu dslouh eb ebal to teg hist sqitoune r.tigh