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submitted by cantaloupe5(87), visit this page
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She’s intaking 450 mOsm per day so she needs to excrete 450 mOsm per day to maintain equilibrium. You can’t just excrete mOsm’s by themselves -- they have to be dissolved in some amount of water.

Let’s say you excrete 450 mOsm with 500 mL of water -- that means your kidneys are concentrating urine to:

450 mOsm ÷ 500 mL = 900 mOsm/L

But the maximum this lady’s kidneys can concentrate urine to is 450 mOsm/L, so she has to excrete more water to get it that dilute. That amount of water is 1 L, because 450 mOsm/1 L = 450 mOsm/L.

Now there’s nothing stopping her from excreting the 450 mOsms in an even more dilute urine -- for example if she drank an extra L of water one day, the kidneys could get rid of that extra L with the same amount of 450 mOsm by diluting the urine to 450 mOsm ÷ 2 L = 225 mOsm/L. But the question asks for the minimum amount of water -- which is 1 L by the kidneys (+ 1 L from the other stuff for a total of 2 L).

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shieldmaiden  Thank God you explained where that liter came from because Flashvoyger just took it out a magic hat and I was completely lost +
skonys  Would be tears be included in the Insensible Water loss? +3
skonys  *my :.( +
ankigravity  So, as another example, if she took in 900 mOsmol/day of solute, she would need to urinate 2 L to clear that + 1 L from the other stuff for a total of 3 L? +


submitted by hello(429), visit this page
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Multiple myeloma = neoplasm of plasma cells.

Plasma cells produce secretory Ab's (aka produce Ab's) -- plasma cells do not have membrane-bound Ig (aka do not have BCR').

To recap: membrane-bound Ig = BCR while secretory Ig = Ab.

Now, anti-idiotypic antibody = antibody against antibody.

Plasma cells do not contain surface Ig -- because plasma cells only be secrete Ab's.

Therefore, anti-idiotypic antibody would not work to target myeloma cells because myeloma cells = plasma cells aka plasma cells lack surface molecules that anti-idiotypic Ab's would need to bind to/target.

See diagram: https://qph.fs.quoracdn.net/main-qimg-ae42c5c9f839fc58a3ce10feaf14c02b

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ali_hassan  sorry what are myeloma cells again? +
ankigravity  Also, the idiotype of an antibody is the portion that binds antigen (versus isotype → IgM, IgA, IgD, IgG, and IgE). The idiotype is also the portion that acts as the receptor binding site for the BCR. +


submitted by nosancuck(102), visit this page
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Yo dawg we all about PVT TIM HaLL

Phenylalanine, Valine, TryptoDANK, Threonine, Isoleucine, Methionine, Histidine, Leucine Lysine

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meningitis  I don't understand what the question is asking... can someone please explain it to me? Patient doesnt eat protein, shes chubby. What does methionine have to do with this? +4
charcot_bouchard  Just basically asking which is essential amino acids. +4
usmleuser007  Essential amino acids (something i came up with) 1. "Three HAL fans will try meth" a. Threonine = Three b. Histidine; Arginine; Lysine = HAL c. Phenylalanine = fans d. Valine; Isoleucine; Leucine = will e. Tryptophan = try f. Methionine = meth +4
nala_ula  They're saying there is a lack of good quality protein -> slight nutritional deficiency. She may have acquired weight but it's not because of protein. So they're specifically asking what amino acid she might be missing due to her subpar diet. Since essential amino acids are those that the body cannot make itself, out off those listed, methionine is the essential amino acid. It's on page 81 of FA 2019. +11
nala_ula  correct me if I'm wrong please :) +
hello  For anyone confused trying to follow @usmleuser007's comment -- slightly modified Essential amino acids mnemonic "Ah, Three fans will try meth" Ah = arginine, histidine Three = Threonine Fans (phans)= Phenylalanine Vil (Will -- German accent pronouncing English word 'will') = valine, isoleucine, leucine, lysine Try = tryptophan Meth = Methionine +2
pg32  Why does @hello and @usmleuser007 mnemonic contain arginine? That isn't in the PVT TIM HaLL mnemonic for essential amino acids... +
paperbackwriter  @pg32 arginine is semi-essential. It is essential in preterm infants who cannot synthesize it https://www.sciencedirect.com/science/article/pii/S0955286304000701?via%3Dihub +
ankigravity  It's also essential in times of positive nitrogen balance (i.e., growing kiddos) +


submitted by asharm10(37), visit this page
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When you are comparing the therapeutic effects of two drugs it's a clinical trial and when both the patients and providers know which drug it's open label. Clinical trial could be done between tx/control or tx/tx. It can't be crossover as there is no wash out phase

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weirdmed51  What’s wash out phase? +
l0ud_minority  @weirdmed51 washout phase is when you are trying to get a drug out of your system example being when treating depression and transitioning from an MAOI to an SSRI you have to wait a couple of weeks for MAO regeneration as to avoid serotonin syndrome. +
ankigravity  To connect to the question, a crossover study is one in which participants serve as there own controls. That is, they get drug A, then they have a washout period where the drug is allowed to clear from their system, then they receive drug B. The researchers can then have the participants serve as there own control. +
ankigravity  Just to add, drug A or B can also be a placebo as well. +


submitted by asharm10(37), visit this page
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When you are comparing the therapeutic effects of two drugs it's a clinical trial and when both the patients and providers know which drug it's open label. Clinical trial could be done between tx/control or tx/tx. It can't be crossover as there is no wash out phase

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weirdmed51  What’s wash out phase? +
l0ud_minority  @weirdmed51 washout phase is when you are trying to get a drug out of your system example being when treating depression and transitioning from an MAOI to an SSRI you have to wait a couple of weeks for MAO regeneration as to avoid serotonin syndrome. +
ankigravity  To connect to the question, a crossover study is one in which participants serve as there own controls. That is, they get drug A, then they have a washout period where the drug is allowed to clear from their system, then they receive drug B. The researchers can then have the participants serve as there own control. +
ankigravity  Just to add, drug A or B can also be a placebo as well. +


submitted by drbravojose(7), visit this page
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FA 2019 p156 Does anyone know how to differentiate the picture labeled Trypanosoma brucei and cruzi?

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footballa  This question is likely not important for two reason: They're both Trypansomastigotes, so of course they look almost the same. You can differentiate these two species clinically as they have very little clinical similarity in patient presentation. For these reasons there's little to no reason you would be expected to differentiate these two species by histology alone +2
snripper  Does Chagas have recurrent fever? Because that's what pointed me to African Sleeping Sickness. +
baja_blast  The history of travel to the Amazon is what pointed me to Cruzi over Brucei but agree it's a tough distinction to make here. In the absence of that detail I would have probably picked Tsetse fly. +1
ankigravity  The trypamastigote on blood smear eliminates all answers except Reduviid bug and Tsetse fly. The fact that she has a cardiomyopathy with recent travel makes Reduviid bug the winner. If she had neuro issues and slipped into a coma following travel to Africa, I would've chosen Tsetse fly. +


submitted by asharm10(37), visit this page
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Unilateral periorbital swelling acute stage of chagas disease

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ankigravity  Known as Romaña sign +


submitted by skuutnasty(8), visit this page
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after rabbit-holing this one for a bit.... this is the photo that demonstrates it best (to me, anyway). must be ilioinguinal n.

enjoy

https://d1yboe6750e2cu.cloudfront.net/i/5e43dd40330f1cd702313cf56b29b8b3f793b00b

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drjo  Ilioinguinal n. derived from L1 is mostly sensory supplying skin of upper and medial thigh root of penis & upper scrotum (males) **mons pubis & labia majora (females) it accompanies spermatic cord through superficial inguinal ring, great pic of this ^ @skuutnasty +
ankigravity  Why is this not at the top.. It's the best image by far. +


submitted by keycompany(351), visit this page
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Nitrogen balance is a measurement of protein metabolism in the body. A negative nitrogen balance indicates muscle loss, as increased amounts of amino acids are being metabolized to produce energy. This increases the amount of nitrogen secreted from the body. Because the amount of nitrogen you are taking in is less than the amount of nitrogen you are secreting, you have a negative nitrogen balance.

This man is malnourished, edematous, cachetic, and has hypoalbuminemia. These clinical findings point to protein malnutrition (Kawashkior Disease), which causes edema due to decreased serum oncotic pressure. Low oncotic pressure in this case is due to protein loss, and hence a negative nitrogen balance.

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drdoom  Nice! +23
dubywow  I knew your last sentence and suspected Kwashiorkor. It's just everything else I did not know. I have not heard or thought of muscle/protein changes in terms of "nitrogen balance" before... and that's why I got this wrong. Nice explanation! +3
macrohphage95  I agree with you in first part but i dont think it has any relation to kwashirkor. It is simply due to cachexia which causes muscle destruction through the proteasome pathway .. +5
zevvyt  also, it says that his albumin is low. +
ankigravity  A few other points related to nitrogen balance. Any patient who is growing (i.e., children, people working out and building muscle) are in positive nitrogen balance and arginine becomes an essential amino acid. +1
drdoom  @ankigravity Wow, this is technically correct! (Didn’t realize “essential” doesn't mean “cannot be synthesized by the body” but rather ”cannot be synthesized in sufficient amounts”; so what qualifies as essential is a bit of a moving target! Thanks!) +
drdoom  Here's the definition from MeSH: “Amino acids that are not synthesized by the human body in amounts sufficient to carry out physiological functions. They are obtained from dietary foodstuffs.” https://meshb.nlm.nih.gov/record/ui?ui=D000601 +
imgdoc  I don't think this has to do with kwashiokor like macrohphage95 suggested. This is cachexia secondary to lung cancer, TNF-alpha increases and causes proteasomal destruction of proteins. This guy is also not intaking enough proteins so negative nitrogen balance is the answer explained above +


submitted by yotsubato(1208), visit this page
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In biology, phase variation is a method for dealing with rapidly varying environments without requiring random mutation. It involves the variation of protein expression, frequently in an on-off fashion, within different parts of a bacterial population. As such the phenotype can switch at frequencies that are much higher (sometimes >1%) than classical mutation rates. Phase variation contributes to virulence by generating heterogeneity. Although it has been most commonly studied in the context of immune evasion, it is observed in many other areas as well and is employed by various types of bacteria, including Salmonella species.

https://www.wikiwand.com/en/Phase_variation

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whoissaad  is it the same thing as antigenic variation? +12
dorsomedial_nucleus  No, antigenic variation involves genomic rearrangement Phase variation can be thought of as MORE or LESS of something. An on/off switch. No DNA is being rearranged, just under or overexpressed in response to the environment. +8
makinallkindzofgainz  This isn't in Zanki, Lightyear, or First Aid, and I don't remember ever learning about this in class. Thanks NBME! :D +21
jurrutia  You wouldn't expect the difference in phenotype of a given organism in a given patient to change because of mutations. It has to be something other than mutation. Phase variation is the only option that sounded like non-mutation. +
l0ud_minority  One of my lectures at my school covered this apparently. In one of their 150+ slide power point handouts small font on slide 65 bottom left hand corner. +1
ankigravity  Don't know if it was in UWorld a year ago, but there is a UWorld question about phase variation. I made card from it stating, "{{c1::Phase}} variation refers to a reversible switch between an “all-or-none” (on/off) expressing phase, resulting in variation in the level of expression of one or more proteins between individual cells of a clonal population." +1
abhishek021196  https://www2.le.ac.uk/projects/vgec/schoolsandcolleges/Microbial%20Sciences/infectious-disease/neisseria-phase-variation Phase Variation - Phase variation is a reversible process that helps bacteria to quickly generate diversity and adapt to rapidly changing environments. One mutation in a 'phase variable' gene can switch expression ON, and another mutation in the same part of DNA will switch the expression of the gene back OFF. DON'T KNOW WHAT DIFFERENCE BETWEEN ANTIGENIC AND PHASE VARIATION THOUGH? +


submitted by usmleuser007(464), visit this page
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In cases of child or adult abuse

1) if there is clear evidence such as if a child states that parents punish by hitting, child is showing fear of parent ---- call child protection right away ( don't need to wait and ask)

2) same thing goes for the adult but call the adult protection services

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osler_weber_rendu  Does anyone not remember Dr Daugherty's lessons which said domestic violence on adults is NOT necessary to report? Instead help them find an escape route in case of an emergency and encourage them to report it themselves. +1
makinallkindzofgainz  @osler_weber_rendu: Domestic violence is not the same thing as dependent adult abuse, such as a special needs adult or an elderly adult (basically anyone who depends on others for care). What you said applies IF the adult is living independently and fully capable to make their own decisions. +8
chaosawaits  REAL STORY: a police officer caused his autistic child to freeze to death by leaving him in the cold to sleep in the garage +
l0ud_minority  I don't see how asking the pt. with the nephew present if he feels safe at home is wrong. You can still proceed to report after but will be able to gather more information. I guess what threw me off was "the most appropriate INITIAL action" in the stem of the question. I hate these questions. I got it wrong after changing my answer from the correct. +
ankigravity  My guess is because you have sufficient evidence to contact them. The nephew refused to leave and I took it as they wouldn't take kindly to me asking the patient if they felt safe. These questions are tricky for sure. +


submitted by seagull(1933), visit this page
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This is a panic attack. Hyperventilation drops pCO2 leading to a respiratory alkalosis. po2 is relatively unaffected (don't ask me how?)

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sympathetikey  Yeah haha I had the same conundrum. +
sajaqua1  If she's breathing deep as she breathes fast, then oxygen is still reaching the alveoli , so arterial pO2 would not be effected. +27
imnotarobotbut  lmao i'm so freaking dumb i thought she was having alcohol withdrawals because it was relieved by alcohol +2
soph  Maybe Po2 is unaffected bc its perfusion (blood) limited not difusion limited (under normal circumstances). +2
charcot_bouchard  PErioral tingling- due to transient hypocalcemia induced by resp alkalosis. +2
rainlad  I believe CO2 diffuses ~20x faster than O2, so increases in her respiratory rate have more effect on her PCO2 than her PO2 +3
usmile1  adding onto Charcot_bouchards comment, I found this: Respiratory alkalosis secondary to hyperventilation is probably the most common cause of acute ionised hypocalcaemia. Binding between calcium and protein is enhanced when serum pH increases, resulting in decreased ionised calcium. Respiratory alkalosis can induce secondary hypocalcaemia that may cause cardiac arrhythmias, conduction abnormalities and various somatic symptoms such as paraesthesia, PErioral numbness, hyperreflexia, convulsive disorders, muscle spasm and tetany. https://www.sciencedirect.com/science/article/pii/S1110184913000615 +4
fatboyslim  Wow very cool. I didn't know alkalosis causes hypocalcemia or why hyperventilation causes perioral tingling. I thought the tingling sensation was due to hypocapnia-induced cerebral vasoconstriction and hence decreased cerebral perfusion. Sort of like when u get choked out you feel tingling (not recommended lol) +1
ankigravity  H+ can displace Ca bound to albumin. So, ↑ H+ (acidosis; ↓ pH) → ↓ Ca binding to albumin → HYPERcalcemia. In contrast, ↓ H+ (alkalosis; ↑ pH) → ↑ sites available for albumin to bind → ↓ Ca (hypocalcemia) +


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We're viewing this slice of the spinal cord from the bottom right? The left right labels always mix me up.

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mcl  Yeah, I just stared at this again for a solid 5 minutes straight up dying. I think if we're going with the L/R labels as they are shown on the image, imagine the patient lying on their stomach with their feet pointed towards you and it should make sense. +10
ankigravity  But why would anyone ever view a patient like that? I mean, in the era of Covid and proning, maybe. +


submitted by momof21234(6), visit this page
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the patient has asbestos which is restrictive (clue was pleural plaques) DLCO is decreased in intra-thoracic conditions (interstitial lung dz etc) and normal on extra-thoracic conditions (muscular issues)

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usmlecharserssss  how FEV1/FVC is normal i cannot get that +4
sammyj98  I think this is standard for restrictive lung diseases. In obstructive the airways collapse during expiration so it's hard to expire, but there's a long drawn out end to epiration as little by little it escapes, leading to a decreased FEV1/FVC. In restrictive pt's just aren't able to move and expand their lungs enough, so when they expire it's of a small volume, but there isn't any collapse involved. It's like a normal expiration just with a restricted volume, making the FEV1/FVC normal. +
spow  @usmlecharserssss In restrictive lung diseases, the ratio is either normal or increased. +4
drzed  And the reason why FEV1/FVC is either normal or increased in restrictive lung disease is very simple: the FEV1 and FVC both decrease because you are restricting airflow, but the FVC will decrease MORE than the FEV1, and thus because the denominator is larger, the fraction either stays normal, or increases slightly Contrast this to obstructive lung disease where you have an obstruction to air FLOW, e.g. the FEV1 will decrease more than the FVC, leading to a low ratio by defition +7
llamastep1  To add to what @drzed said, fibrosis causes radial traction on the airways therefore increasing FEV1/FVC. Theres a Uworld q on it +1
ankigravity  And just to add to what @llamastep1 said, radial traction is the relative force exerted on the airways by the interstitial tissues. It is increased in fibrotic conditions due to tensing of the tissue and decreased in conditions that destroy or reduce strength of interstitial tissue. +


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Can anyone explain how 10cm H20 positive PEEP leads to Peak Inspiratory PA, End Tidal PA, Peak Inspiratory Pip and End Tidal Pip all being positive?

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tea-cats-biscuits  In PEEP, bc of how mechanical ventilation works, all the inspiration part of breathing is done by the machine actively pushing air into the lungs. As a result, there is no negative pressures in the system compared to the normal lung which needs the negative inter-pleural pressure to draw air in. +28
yotsubato  " As a result, there is no negative pressures in the system compared to the normal lung which needs the negative inter-pleural pressure to draw air in. " Thats totally what threw me off. TIL +
veryhungrycaterpillar  Why would the end tidal IP not be negative though? Sorry I must be completely misunderstanding something. +
ankigravity  Alveolar pressure will ALWAYS be POSITIVE. Normally IPP is -5 after EXPIRATION (END-TIDAL) and -8 after INSPIRATION. Here we are giving +10 with Ventilation. That will overcome normal END-TIDAL (-5) making END-TIDAL IPP to +5. (Copied from another comment because it explains it pretty well; credit to u/lukin4answer) +


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