NBME Answers : artist90's page

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submitted by nwinkelmann(185),

Does anyone have a good explanation for why decreased levels of inhibin is wrong? From my understanding, inhibin and activin work together, in that inhibin binds and blocks activin leading to decreased feedback on hypothalamus and activin increases FSH and GnRH production.. thus, if you decrease inhibin then you would have increased activin which would lead to increased GnRH and FSH, right? I found one article talking about it in regards to puberty, but it seems to be a hypothesis/not confirmed at this point... is that why? But still... how do I rule it out on a test?

yb_26 I also picked decreased inhibin. may be it was one of the "experimental questions", which are not even counted on the real exam +

artist90 Inceased FSH will lead to spermatogenesis and spermiogenesis NOT Increase in Testosterone which is causing increased Height of this pt +1

artist90 Inhibin B only has negative feeback on FSH not GnRH. see the diagram on the topic of semineferous tubules in FA. Testosterone has a negative feedback on BOTH LH and GnRH +1

usmile1 Kind of like how nocturnal pulsatile GNRH release occurs during sleep to stimulate growth (FA page327), the same thing happens for puberty. Pg 325 in FA, "pulsatile GnRH leads to puberty and fertility." It doesn't explicitly state during sleep, but pulsatile release of GnRH leading to pulsatile release of LH and FSH will lead to puberty. Puberty starts in the brain, its onset really has nothing to do with decreased inhibin levels which happens in the testes. hope that makes sense! +1

submitted by nwinkelmann(185),

yb_26 I also picked decreased inhibin. may be it was one of the "experimental questions", which are not even counted on the real exam +

artist90 Inceased FSH will lead to spermatogenesis and spermiogenesis NOT Increase in Testosterone which is causing increased Height of this pt +1

artist90 Inhibin B only has negative feeback on FSH not GnRH. see the diagram on the topic of semineferous tubules in FA. Testosterone has a negative feedback on BOTH LH and GnRH +1

submitted by lsmarshall(262),

The most direct path, and most likely path, for breast cancer to metastasize to the vertebra are the intercostal veins. This was on an earlier NBME test as well. Breast cancer will cause mixed, lytic and blastic lesions once in bone.

On an unrealated note; I finally came up with a decent way to remember lytic vs. blastic cancers in bone!

kIdneY and thYroId cause lYtIc

prostate > blastate > blastic

Two breasts > two types of lesions > B reast causes B oth

Two lungs > two types of lesions (depending on type of lung cancer)

small-cell lung > "small blasts"

non-small cell > lytic

artist90 VEINS: 1-Intercostal veins drain into Azygous vein which drains into SVC BUT some blood from this Azygous vein is also draining into BATSONS VERTEBRAL VENOUS PLEXUS how the breast cancer metastasizes to vertebral column. 2-Internal thoracic(mammary) vein drains directly into Brachiocephalic vein. 3-Lateral thoracic vein drains into Axillary vein which drains into Subclavian vein which drains into Brachiocephalic vein. ARTERIES ARE DIFFERENT: Subclavian artery----branches into---Internal thoracic(mammary) artery---Intercostal arteries. Internal thoracic artey is used for CABG if there is 1 vessel block. +6

submitted by lsmarshall(262),

Urea Cycle Disorders > Isolated severe hyperammonemia (> 1000; i.e., no other severe metabolic disturbances

Ornithine transcarbamylase deficiency > (most common urea cycle dis.) orotic acidemia/aciduria, hyperammonemia

Organic Acidemias > Hyperammonemia, anion-gap acidosis, ketosis (from hypoglycemia)

Medium-chain acyl-CoA dehydrogenase deficiency > Hyperammonemia, hypoketotic hypoglycemia (seen in β-oxidation disorders, EXCEPT adrenoleukodystrophy)

Liver dysfunction > Hyperammonemia, LFTs messed up, older pt.

lsmarshall Summary of metabolic issues relating to hyperammonemia +4

seagull i'm leaning towards Ornithine transcarbamylase deficiency. +2

notadoctor Not sure why this isn't considered a mitochondrial disorder since the issue is Ornithine transcarbamylase deficiency in the mitochondria? +2

charcot_bouchard if it was mitochondrial disorder no one would escape +1

wowo figure in OTC deficiency, they might have to explicitly mention the orotic aciduria AND typically presents earlier, around 24-48hrs of life after they've fed (at least per BB) + also per BB, propionic acidemia and MM acidemia have an onset of weeks to months and lead to build up of organic acids --> acidemia in addition to hyperammonemia (not sure why, but several aa enter the TCA cycle via propionyl CoA --> methylmalonyl CoA --> succinyl CoA, but now this is defunct d/t enzyme deficiencies...?). Anywho, propionic acidemia described on FA2019 p85, but doesn't list hyperammonemia +2

artist90 i think it cannot be Ornithine transcarbamylase deficiency bc it is XR disease. this pt has a healthy 2yr old brother which rules out X-linked recessive disease correct me if i m wrong +

artist90 it is 100% Propionic acidemia Uworld Q-id: 1340. it is an exact copy question of uworld. i got it wrong bc i forgot these are organic acids. But i am still confused on 2 things 1-how does acidosis cause Hypoglycemia and Ketosis. 2-why is Ammonia elevated in these pts bc urea cycle will be fine? +

yb_26 1) hyperammonemia is seen in all urea cycle disorders except arginase deficiency 2) organic acids directly inhibit urea cycle => hyperammonemia (from UWorld) +1

yex According to UW, there is another question # 1341. This one refers to methylmalonic acidemia (ORGANIC ACIDEMIA). HYPOGLYCEMIA results from overall increased metabolic rate leading to increased glucose utilization and direct toxic (-) of gluconeogenesis by organic acids. The presence of hypoglycemia leads to increased free fatty acid metabolism that produces KETONES, resulting in a further anion gap met acidocis. Finally, organic acids also directly (-) the urea cycle, leading to HYPERAMMONEMIA. +5