NBME 19 Block 1 answers with explanation

ALL ANSWERS ARE CONFIRMED FROM ONLINE NBME

1- f

it's marcus gunn pupil,you should know that it's decreased bilateral pupillary constriction when light is directed to affected eye.

the lesion is in the right optic nerve(afferent) as the question describes lesion when flash is directed to right eye.

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2- c

odds ratio equals a*d/b*c
it's a direct question,you should know the equation well
2*2 table is present in FA ,please know it by heart

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3- d

let's analyse keys:

alcoholic+foul smelling sputum(means bacterial infection ie.anaerobes)+episodes of unconsciousness

this is most probably aspiration pneumonia which may lead to lung abscess (the x-ray finding in the choice)

if you don't know how abscess looks like in x-ray,google search will help a lot.

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4- e

an easy question,remember that accumulation of lactate causes a decrease in ph and eventually fatigue .

lack or decrease in oxygen supply during heavy exercise will shift metabolism to anaerobic metabolism,which will lead to depletion of glycogen and accumulation of lactate

so in fatigue: lactate increases but ph decreases

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5- b

factors determining risk of postmenopausal osteoporosis are:

ethnicity: african americans have low risk than caucasians 

exercise: decreases risk

diet : high Ca diet decreases risk

although socioeconomic history (choice f) may reflect diet and nourishment status  , but choice b (dietary history) is more specific

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6-d

a typical case of rheumatoid arthritis

middle aged woman + affection of proximal interphalangeal joint with sparing of distal joints
biopsy of RA will show proliferative granulation tissue which is known as pannus (choice d)

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7-c

the x-ray in the question shows hyperlucent area in left chest most likely pneumothorax,

sudden left side sharp pain + dyspnea support diagnosis
in pneumothorax: air entry to pleura will lead to loss of negativity of intrapleural pressure (choice c)

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8- c

Exercise distends the vessels, reducing their resistance to blood flow. Thus, the base of the lung receives more blood flow than the apex. During exercise, vessels can be recruited, increasing the total cross-sectional area and reducing resistance. Lung volume also passively alters pulmonary vascular resistance

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9- d

pulmonary hypertension leads to increase right ventricle afterload

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10- c

very high beta human chorionic gonadotropin as well as large uterus is most likely a case of mole
in ectopic pregnancy this hormone is slightly increased

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11- e

of course it's vit D which is responsible of Ca absorption

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12- c

both warfarin and dicumarol are structurally related
they inhibit enzyme epoxide reductase which activate vit K ,inducing vit K deficiency like state

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13- d

metronidazole causes disulfiram like effect,which is shown in the question as vomiting , flushing and headache

metronidazole is the first choice to treat trichomonas vaginalis

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14- c

propranolol is a non selective beta antagonist:

beta 1 antagonism >>> decreases heart rate&contractility >>> decreases cardiac output

beta 2 antagonism >>> vasoconstriction >>> increases total peripheral resistance

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15- b

you should know mechanism of aspirin by heart and the step on diagram

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16- c

The patient will have shallow and rapid breathing to compensate for the decreased tidal volume..as deep breaths will cause pain.

nothing is wrong in the airways (obstructions) the airway resistance remains same !!

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17- e

blood-testes barrier are formed from tight junctions between sertoli cells

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18- a

age is the clue 

after 18 >>> antisocial personality disorder

before 18 >>> conduct disorder

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19- a

AMP stimulates glycogen phosphorylase via addition of the phosphate group on it ( remember it through glucagon pathway),this increases affinity of enzyme to substrate

And as you can clearly see from the enzyme substrate curve that it acts as an activator 

So, it is allosteric activator !

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20- b
heparin induced thrombocytopenia,an easy question

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21- b

US detects nuchal translucency but NT is just screening. Since there is predisposition we should do chorionic villi sampling
Chorionic villi sampling can actually detect chromosomal abnormalities as early as 10 weeks of pregnancy before you have to wait several weeks (15 to 20) to be allowed to do amniocentesis. Testing phospholipids is not gonna tell you anything about the fetal chromosomes just give you idea On their surfactant levels.

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22- c

flutamide is a non selective inhibitor at androgen receptor while leuprolide is a GnRH agonist but it action varies with dose fashion:

it has activity of agonist when given pulsatile,but when given continuously,it acts as antagonist as it downregulates GnRH receptors on pituitary

when leuprolide is decided to be given continously,it causes surge at first which will lead to increase LH and androgens,so we use flutamide to block this initial increase

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23- e

the debate here is between NRTIs and protease inhibitors 

but there are 2 clues:

- nearly all protease inhibitors cause lipodystrophy while only zidovudine and stavudine from group of NRTIs cause lipodystrophy so the choice of protease inhibitor is more likely the right answer

- protease inhibitors cause hyperglycemia and hypercholesterolemia which are present in the question

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24- c

all values indicate obstructive lung disease

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25- c

bruit over posterior flank > renal artery stenosis

hypertension supports diagnosis

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26- c

this is a case of SIADH as indicated by decreased plasma osmolality and increased urine osmolality

small cell lung cancer can secrete ADH as paraneoplastic syndrome causing SIADH

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27- g

the only drug from mentioned drugs that is known to cause osteoporosis is corticosteroid

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28- b

it is easy to answer this question as from question stem , it looks like an allergy case,in which histamine is released causing marked hypotension , but the very important concept you should know is that opioids cause IgE independent mast cell degranulation

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29- c

3rd pouch forms inferior parathyroids as well as thymus

4th pouch forms superior parathyroids as well as ultimoobrachial body

so if 3rd pouch is defective , there will be no thymus formation but there will be parathyroids (superior parathyroids formed from 4th pouch)

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30- c

dynein arm is know to be responsible of retrograde movement while kinesin is responsible of anterograde movement

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31- e

low back pain + osteoblastic lesions >>> prostate cancer >>> increased prostatic specific antigen PSA

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32- e

it is a case of acute rejection which is mediated by lymphocytes

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33- a

a retrograde study which is divided into two groups according to presence of disease

it would be cohort if the division was according to exposure status

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34- e

a case of androgen insensitivity syndrome

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35- d

serotonin is synthesized from tryptophan ,so increase tryptophan in food will lead to increase serotonin

note that niacin is also formed from tryptophan but giving niacin will slightly affect serotonin level because more tryptophan will be available to form serotonin

so choice d is better

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36- c

from the scenario ,it is motor cortex affection

it is letter c than represent face area

google cortical homunculus

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37- a

A site is empty...waiting for incoming of a charged aminoacid tRNA.

Only first amino acid comes to P site, the rest enter at A site, this is a growing chain hence amino acid enters at A site.

P site occupies by the growing peptide chain

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38- f

at point X ,respiration stops

there are many mentioned drugs that can cause this,but from question,phrenic nerve activity is not affected,so the problem must be in neuromuscular junction

the only drug mentioned that can affect neuromuscular junction is tubocurarine,which act as ACh competitive antagonist

tetrodotoxin will affect the nerve itself not neuromuscular junction

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39- b

It is an easy question

it must received a marrow transplant from a male ,so progenitor cells will give XY daughter cells

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40- a

it is a serious systemic infection and must by treated with systemic antifungal (amphotericin B) 

fluconazole can be given as maintenance therapy but amphotericin B must be given acutely first

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41- b

you should know that kidney also shares in gluconeogenesis

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42- b

Surfactant normally decreases the surface tension on the alveolar walls, thereby allowing them to expand easily. This neonate has decreased surfactant levels due to immaturity, because of which his alveoli will have higher surface tension, leading to higher collapsing pressures. This will lead to more alveoli being collapsed---> leading to less air in lungs ---> leading to decreased functional residual capacity.

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43- a

hemoptysis  + hematuria + linear IgG deposition >>> GoodPasture syndrome >>> crescent formation

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44- d

1. Both parents must be carriers (Aa each) for the disease to be passed onto the brother.

2. For the parents to have a child that has this autosomal recessive disease, both must be carriers.

3. For the parent's punnet square, Aa x Aa,

a. 2 Aa, 1 aa, 1 AA

b. The male must be either Aa or AA as he doesn't have the disease. We need to calculate the odds of the male being a carrier --> 2/3

4. For the 30yo female, the chance of having the disease is calculated via hardy-weinberg; you are looking for 2pq. q^2 = 1/40,000. q= 1/200 and p=199/200 (essentially 1). 2pq = 2*1*1/200 = 1/100 chance of being a carrier

5. The odds of the kid having the disease is the same punnet square from step 3. aa = disease, therefore the odds are 1/4.

Run the final calc:

(2/3) * (1/100) * (1/4) = 2/1200 --> 1/600

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45- b

its so straight forward
CD8 cells attack cells expressing MHC 1 which is seen in virally infected cells and hepB virus is a DNA virus that replicates in the hepatocytes....
Hence the hepatocytes express MHC1 with endogenous processing of viral proteins and attract CD8 t cells

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46- a

Because prinzmental is a neurological construction of coronary vessels (mostly idiopathic and responds to CCBs)

other choices are wrong themselves

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47- b

epigastric pain + irritable&forgetful + distal motor weakness + impairment of consciousness

all of these direct to lead poisonong

in lead poisoning there are :

basophilic stippling in blood smear

sideroblasts in bone marrow

Be careful and read what he asked first ,in blood or bone marrow ?!

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48- a

all lab values indicate anemia

why not b,c,d,or e ? >>> as arterial Po2 &Pco2 are normal 

venous Po2 and o2 content are decreased as tissues try to compensate anemia and decreased o2 amount by increasing percentage of o2 extraction

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49- a

coxsackievirus is the most common virus causing myocarditis and most commonly occurs after upper respiratory tract infection

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50- d

widening of hepatic venules + increased hepatic vein&wedge pressures with normal right atrial pressure >>> Budd Chiari syndrome

if right atrial pressure is also increased , it will be right sided heart failure