# NBME 16 help

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#### shubz123

##### New Member
10+ Year Member
Hi all,

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1) you said that for first order kinetics, a fraction is lost per unit time. I'm not sure but if this is the way to approach it, but I thought about it like this....in 2 hours 2.5mg is lost, that is 20% of 12.5mg. I would imagine that in another 2 hours, another 20% would be lost. Thus, in 2 more hours 2mg (20% if 10mg of course) more would be lost, giving you 8mg. E

2) For this one, I was thought about it this way....if there is a prevalence of 1/100,000 males getting the X-R chromosome and there is a 50% chance of getting the "Diseased" chromosome from mom, there should be twice that amount of women that are carriers. Thus, 2/100,000 = 1/50,000. B

1) First-order kinetics mean the same fraction is lost/metabolized per unit time. In the first two hours, 10/12.5 = 80% is lost, so after the next two hours, 0.8 x 10mg = 8mg should remain = E.

2) Are you sure you copied the wording of this question down right? The disease prevalence in heterozygous females would be zero because it's XR, not XD, but if you mean what is the diseased allele prevalence, then the carrier frequency would be 2pq, where p~1 because q=1E-5 (1/100,000) and p+q=1. So 2 x 1 x 1E-5 = 2E-5 = 1/50,000 = B.

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Thank a lot all!!

I was wondering if you weren't too busy that you could help me with another stat question. Keep getting these all wrong.

Can't seem to figure this one out.

A screening program is initiated for detection of vaginal C. trachomatis infection among first year college women students. At the initial screening Chlamydiae is found in 500 of the 2500 students. One year later, the screening shows that the infection has affected an additional 200 students. Which of the following is the annual incidence of C. trachomatis infection in this population of women students.

A.) 8%
B) 10
C) 16
D) 20
E) 28

Incidence is all new cases over the total population. So I did 200 over 2500 and got 8% but it was wrong,

Remember that incidence is the number of new cases over the population AT RISK. So in this case, the question told us that 500 of the 2500 tested positive for the disease. This leaves 2000 at risk for the next year. Thus, 200/2000= 10%. B

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How did you guys find this NBME (16) compared to the others in terms of difficulty?
Just finished it now and ended up scoring lower than the last 3 NBMEs I did over the last month (#6, 7, 11)....writing Step 1 next week.

and adding PCOS cause inc LH inc insulin due to resistance occur

Need help with the above.. thanks

THANK YOU SO MUCH TO ALL FOR THE REAL HELP

yeah i wrote that normal
i got it right

for 2 i would put C because you are evaluating a risk factor.

are you sure while coughing vocal cords are open?

are you sure while coughing vocal cords are open?
if they were closed, that would be a valsalva maneuver. you can ONLY move air thru the vocal cords and make any sort of sound when the cords are open.

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there was a question regarding ferritin gene..that no effect seen on western and northeran blotting..is it due to mature mRNA?

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thanku

for 2 i would put C because you are evaluating a risk factor.[/quote]
are you sure its C?

evaluating to see if working at a foundry caused MR in kids, hence working there is a the RF. So you get 2 groups equally MR children then determine if their parents working at the foundry [hence RF] had any impact on their condition.
what makes you think it is not C? [again, any discussion is good discussion]

i have very bad concept of control group..as i marked B got it wrong..i though non diseased with no riskfactor

i have very bad concept of control group..as i marked B got it wrong..i though non diseased with no riskfactor
Are u sure You marked it B ?

i still feel i wrote B but mine was correct
now i am confused

you have no idea about disease till now , you are just selecting 2 groups before a study
one with the risk factor and the other without risk factor

for 2 i would put C because you are evaluating a risk factor.

yea as worded, that makes sense. However, the experimental design is probably this:

Take kids w/ parents at the foundry and evaluate them all for motor impairments.
Takes kids w/ parents not at the foundry, evaluate them for motor impairments.

Compare the two groups. So in that sense, B is the better answer because it properly sets up a comparison.

I think that question is just poorly worded and doesn't really test your ability to design an experiment.

yea as worded, that makes sense. However, the experimental design is probably this:

Take kids w/ parents at the foundry and evaluate them all for motor impairments.
Takes kids w/ parents not at the foundry, evaluate them for motor impairments.

Compare the two groups. So in that sense, B is the better answer because it properly sets up a comparison.

I think that question is just poorly worded and doesn't really test your ability to design an experiment.
I agree on that, I see why B is a better choice.
So in what case would C be a better option? [srly sometimes they make the most straight forward concept into something so confusing!]

just checked i have got this right..but now i dont remember what i marked:-( Oh my God whats going on

Parietal cell -> B ; Fried egg appearance, pale looking

6. Flow rate = Velocity * Area; 2.4 L/min = 2*20*(60sec/1min)*(1L/1000cc)

35. Confidence interval; Decrease in sample size means greater width; CI = Mean +/- SD/[sqrt(N)] where N is sample size

6. Risk = 32/1000 = 0.032 which is constant; This following year, 32 are removed so population at risk is 1000-32 = 968; Risk the following year = 0.032 * 968 = 31

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27. Signs described are characteristic of LMN lesion. So its degeneration of motoneurons in lumbar cord.

thankyou so much

She has ALS -> degeneration of motor neurons.

this one with explaination .

You forgot to convert from L/sec to L/min. Q = Av; solve for Q as you did (4ml/sec), convert to L/min.

plz explain

Increase in width, rather than decrease. Confidence interval goes up with fewer measurements because you don't know where the true mean. One off reading can throw your entire data set into whack.

Basically, how confident are you. If you flipped a coin 5 times and came up heads 4 times, is that enough to say that the coin is rigged? What happens if you flipped it 5,000 times and got 4,000 heads? That's pretty much the same principle being tested in this question.

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never mix alcohol and acetaminophen.

A -> no sense.
B -> no because that's not what etoh does to the liver.
C -> no, makes no sense again.
D -> yes, because more p450 -> more tylenol shunted to p450 enzymes -> more NAPQI -> liver toxicity
E -> not related to tylenol toxicity in the liver.

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6. Flow rate = Velocity * Area; 2.4 L/min = 2*20*(60sec/1min)*(1L/1000cc) so what would be answer?4? after converting L/sec

Flow = Area * Velocity
Q = V * A
Q = 20 cm/s * 2cm²
Q=40 cm³/s
Q=2400 cm³/min (1cm³=1ml) --> 2400 ml = 2.4 l

its E..there is accumulation of Interstital cells
can you explain that one, they looked normal to me lol then again Iam bad with that stuff

Hey, if anyone can explain the following biochem question I'd greatly appreciate it! thanks in advance.

It's the enzyme most proximal to the block, so G3pase is the right answer. Aldolase is involved with fructose metabolism.

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Ok i'm so sorry! Just one last question. Sorry for posting so much it's just my test is next week!!!
Its large
re-read the question; it talks about hanta A. Based on that diagram, anytime A is involved in the large segment, it wont grow. When B replaces A in the large segment, the virus grows, so Large must be the problem here

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Ok i'm so sorry! Just one last question. Sorry for posting so much it's just my test is next week!!!

it's the long segment, whenever that segment is missing, the virus doesn't grow at high temperatures. experiment 1 and 6 prove that M and S don't do dick for temperature, experiment 3 shows that L confers heat resistance.

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Dude has sciatica, evidenced by the radiation down the leg. Therefore, C.

CK+, ANA+ sounds like Dermatomyositis, especially given the upper extermity proximal muscle weakness. I've never seen it present that early in any material though.

yea, it's Pcomm. 2nd most common place for berry aneurysms and it also presents with CN III palsy.

yep, physostigimine is the preferred anti-muscarinic because it penetrates CNS.

sounds like a testicular torsion, esp with radiating pain to the groin.

only ventricular cardiac cells are permanent cells in the above list.
stole my thunder bra! lol
if you have a renal calculus near the bladder it can radiate to the groin as well, thats why I picked renal calc

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stole my thunder bra! lol
if you have a renal calculus near the bladder it can radiate to the groin as well, thats why I picked renal calc

****, good catch. I misread that as urethral calculus. It does sound like a ureteral block more than a testicular torsion.

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resp phys the answer is E, if you put in a lot of fluid, you increase the hydrostatic pressure, favouring filtration.

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for vaccine, she has walking pneumonia; influenza vaccine works best

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Thanks Fatalis! Do you happen to have any idea about the micro pharm question?

Thanks Fatalis! Do you happen to have any idea about the micro pharm question?

looks like cryptococus, so ampho B

infiltrate/consolidation rules out viral infections.

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Thank you notbobtrustme! Ugh I thought it cryptococcus but then it looked so small relative to everything else going on in that picture so i took for just stain smears. Thank you again.

looks like cryptococus, so ampho B

infiltrate/consolidation rules out viral infections.
Yeah, Ampho B is the correct answer. Had this one right. Although, don't you think it's blasto? Pairs of cell with broad base budding.

Influenza vaccine is also correct (non-productive cough, malaise, muscle pain)

Dermatomyositis (although the pt being a 12 year old freaked me out for a sec)

Remember that incidence is the number of new cases over the population AT RISK. So in this case, the question told us that 500 of the 2500 tested positive for the disease. This leaves 2000 at risk for the next year. Thus, 200/2000= 10%. B
My issue with this question, yes incidence is new cases/total pop at risk, but getting chlamydia one year does not make you any less at risk for getting it the next year...Also, when they say "an additional 200 test positive " the next year, I interpret that as, the next year there are 700 who test positive, so 700/2500 = 28%.
Can anyone who got this question right say what their answer was? Was B actually the right answer?

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Yeah, Ampho B is the correct answer. Had this one right. Although, don't you think it's blasto? Pairs of cell with broad base budding.

ya, it might be blasto. The picture was really small/low quality, but good enough to know it was a fungus. Plus the clinical picture painted a picture that suggested a fungal infection.

I thought it was blasto bc they always look like semi moons but ya the pic was really hard on the eyes lol

Sorry for not having the question and answers in front of me as I was pressed for time and didn't screen cap it.

1. Pt. went to Kenya, watery + bloody diarrhea, 12 micrometer trophozoites with erythrophagocytosis. What organism? None of the malarias was an answer choice.

Sorry for not having the question and answers in front of me as I was pressed for time and didn't screen cap it.

1. Pt. went to Kenya, watery + bloody diarrhea, 12 micrometer trophozoites with erythrophagocytosis. What organism? None of the malarias was an answer choice.

1. Sounds like Entamoeba histolytica. In my micro class the prof mentioned you can see erythrocytes that they've phagocytosed inside them.

Just took 16 this afternoon...did quite a bit better than 15 but still thought it was pretty rough.

So, if we're excluding reinfection, would it be 200 new cases divided by 1800 people at risk??

200 new cases divided by 2000 people at risk.

Initially, they found 500 out of 2500 had chlamydia. For the incidence for the next year, you assume that you're still dealing with the same total 2500 students, but you have to subtract the 500 that were already diagnosed last year with chlamydia. So that leaves you with 2000. If 200 students acquired the infection in the last year, it's 200/2000 for the incidence, or 10%

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Thank you!! I don't know why I thought you had to subtract people w disease (even new cases) from population at risk. I figured since they have the disease, they're no longer at risk? Am I confusing this with something else??

Because with a case control you already have your outcome and you're looking at exposure.
This statement helped a lot, so does this mean that the answer for 50 (just posted) should be "c"?
Please also look through the other questions
Thank you very much!!