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NBME 23 Answers

nbme23/Block 2/Question#4 (58.1 difficulty score)
An 18-year-old woman comes to the physician ...
Maximum oxygen consumption (VO2max): decreased;
Venous blood lactate: increased;
Energy production by glycolysis: increased


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submitted by joker4eva76(25),
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drdoom  ... pyruvate is shunted over and is used by LDH (lactate dehydrogenase) to generate lactate*. +3  
chris07  It's hinted in the answer, but I would like to clarify: max O2 consumption is decreased because O2 is consumed in the Electron Transport Chain, which occurs in the mitochondria. With the mitochondria not working, the ETC cannot work, and thus there is less demand for Oxygen. +17  
masonkingcobra  Mitochondria are the powerhouse of the cell +50  
uslme123  Apparently ragged red fibers are the result of coarse subsarcolemmal or intermyofibrillar mitochondrial accumulations.. +2  
mnemonicsfordayz  As @chris07 said, less O2 is being consumed in the ETC... but I also was thinking that the diaphragm is a muscle and if the mitochondria in her diaphragm are also not functioning, then she's not breathing properly and less O2 is being inhaled and therefore decreasing her oxygen consumption. Is that totally off base or am I just grasping at straws here? +  

submitted by nwinkelmann(285),
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yrroS st'i os g!lon

djtallahassee  lol yea. I thought they were trying to say there was an abnormally large amount of mitochondria present which made me get the opposite answer :/ +1  
alexxxx30  no I so agree. The grammar was completely wrong (clearly whoever wrote the question needs to work on english). This was very frustrating to me because I recognized that it was ragged red fibers, but then the wording made me doubt my own knowledge (thinking how could the test writer mess that up?). abnormal accumulations either means too much or too little. accumulations of abnormal mito means thee mitochondria is faulty. Correct grammar is putting the adjective right next to the word it is describing. So this was definitely wrong and I share your sentiment. This really frustrated me! +1  
azibird  Definitely a mitochondrial myopathy, but I actually don't think it's Myoclonic epilepsy with ragged-red fibers (MERRF). This normally entails Myoclonic jerks, Generalized seizures, Cerebellar ataxia, and Dementia (according to Amboss). Maybe it's CPEO (chronic progressive external ophthalmoplegia): progressive extraocular ophthalmoplegia with bilateral ptosis. Not sure which one would account for her poor exercise tolerance. Either way, recognizing it's mitochondrial is enough. +  

submitted by soph(55),
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pt whit gessrvpieor eumcsl -ksnesg&;awet- sper lceumss nto wingkor -;>- eecsreda gynoex tonmsp.iuocn on oe=xgyn no brceaio ebiolmatsm &t;--g irsaenec noesuv ,actetla soal uoy eepk nogdi oarecniab gcyilsoysl necsi uoy acnt og ot ACT t--&;g sncierea yeegnr noocdiuprt iav slioglsyyc ):

submitted by diabetes(25),
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nca ymboesod ixalepn owh nyeger riconudpot yb ylicossgly ,ncesaedri nices raciobe icllsyygso updcero 32 net P,mceAoTarp ot 2 etn PAT hrthoug eoriacabn cysyogslil ?

diabetes  i think the stem should be "energy production by an anaerobic glycolysis " +3  
blueberrymuffinbabey  yeah that's the bit that tripped me up too. i get that there would be increased glycolysis in general to compensate for lack of TCA function but...the fact that it says "energy production by glycolysis" is kind of misleading/confusing. +  
thotcandy  technically, glycolysis is the reaction that happens in the cytosol that generates pyruvate and 2 net ATP. after that it's TCA and Oxidative phosphorylation, which occur in the mitochondria. By definition, glycolysis is anaerobic - which is why they hammer the fact that RBC undergo glycolysis only into our heads. +1  
thotcandy  technically, glycolysis is the reaction that happens in the cytosol that generates pyruvate and 2 net ATP. after that it's TCA and Oxidative phosphorylation, which occur in the mitochondria. By definition, glycolysis is anaerobic - which is why they hammer the fact that RBC undergo glycolysis only into our heads. +  
targetmle  i got it wrong because of this as i thought ATP will be decreased in anaerbic glycolysis, but proabably it was mainly 'glycolysis' is increased +1