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NBME 20 Answers

nbme20/Block 3/Question#19

A 23-year-old man comes to the physician because of ...

Area labeled ‘B’ (Mitochondrion)

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 +6  upvote downvote
submitted by jinzo(8),

A - nucleus ( with nucleolus inside ) B - mitochondria C - RER ( you can see attached ribosomes ) D - ?? may be lysosomes E - glycogen granules

 +2  upvote downvote
submitted by usmle11a(32),


guys this video explains alot

 +1  upvote downvote
submitted by qfever(12),

Does anyone know what are A, C, D? For C not sure if it's pointing to the ribosomes on RER.

(I'm assuming E is glycogen granules based on a comment below!)

drdoom  see @jinzo’s comment above +  

 +1  upvote downvote
submitted by usmile1(33),

does anyone know what the structure E is pointing to?

thomasburton  Not sure looks like it might be free ribosomes or other such small cytosolic structure (I picked E too, thought B looked way too big!) +  
targetusmle  same here!! marked e thinking of it as a mitochondria +1  
msyrett  Glycogen Granules! They are not membrane bound and float freely in the cytoplasm. +1  

This patient presents with a mitochondrial myopathy since the disorder is inherited from the mother. Mitochondrial myopathies show “ragged red fibers” on muscle biopsy due to the accumulation of diseased mitochondria in the subsarcolemma of the muscle fiber.

katsu  Mitochondrial myopathies—rare disorders; often present with myopathy, lactic acidosis, and CNS disease, eg, MELAS syndrome (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes). 2° to failure in oxidative phosphorylation. Muscle biopsy often shows “ragged red fibers” (due to accumulation of diseased mitochondria). +  

Anyone find a problem with the stem? Seems to me that it doesn't help to state "however, his father's sister and children are unaffected". We already know the mutation runs in the mother's side, right? It seems like that statement doesn't discard nor confirm any inheritance pattern. Why would we care about the patient's father's side?