Nbme 12 Block 4 Some Explanations

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BLOCK 4 (not 1)

http://www.usmleforum.com/files/forum/2013/1/749199.php

* Re:NBME 12 Block 1 q1-50 Discussion

#2951245

ae0704 - 09/15/13 13:48 Q1:

Answer: B

Ethical Situations: Patient Refuses a necessary procedure or want an unnecessary procedure--> Attempt to understand WHY the patient wants/or doesnt want the procedure... Address underlying concern.

Source FA, Behavioral

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#2951251

ae0704 - 09/15/13 13:59 Q2:

Answer: A

Chlordiazepoxide, is a benzodiazepine, (Bz,opiates OVD has been shown to produce hypoventilation) This along Alcohol causes an additive/further CNS depression and hypoventilation (Pte. has 9resp/min) which will cause the retention of CO2 (Hypercapnia) leading to a decrease ph-- Respiratory Acidosis (⇓ Po2 ⇑PCO2 ⇓pH).

Source FA, Renal and Kaplanqbank.

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#2951254

ae0704 - 09/15/13 14:02 Q3:

Answer: E

Ethical situation: Patients continues smoking believing cigarettes are good to him: Ask Patient how he feels about quitting..offer advice of cessation if patient is willing to make an effort to quit.

Source FA, Behavioral.

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#2951262

ae0704 - 09/15/13 14:10 Q4:

Answer: D

Leukocyte Extravasation: Rolling: Neutrophils rolls on the endothelium via LOOSE

BINDING/ADHESIONS of Sialylated carbohydrate group, such as Sialyl Lewis or PSGL-1 to L-Selectin on neutrophils or E-selectin/P-selectin on endothelial cells. Cytokines stimulation greatly increses the expression of endothelial selectins.

Source, UWqbank

Additional info, just so you know, Integrins, are a type of tight adhesion.

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#2951297

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Q5: Answer: F

Ehrlichiosis: type of Rickettsial disease (Transmitted by tick, an obligate intracellular organism) Presents: N/V, photobia, muscle and head aches, Fever.

Labs: Decrease WBC and Platelet. Increase Transaminases

peripheral smear: Granulocyte contains berry-like cluster of intracellular organism.

Treatment is also a Tetracycline, whose MoA: Binding to 30s, prevent attachment to aminoacyl-tRNA..AKA Elongation of protein synthesis.

Recall the uses of Tetracycline: VACUUM THe BedRoom. R stands for Rickettsia.

Source, Micro Rickettsial disease and Kaplanqbank

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#2951313

ae0704 - 09/15/13 15:19 Q6:

Answer: E

Myxoma: Pedunculated, gelatinous mass, most common(mc) seen in Left Atrium(LA) (mc 1〫cardiac tumor in adults). mc in females. Described as Ball-valve obstruction of LA.

Presentation: Multiple syncopal episodes. can lead to systemic embolization and for this can presents as a stroke.

Produce IL-6 reason that other presentation correspond to constitutional symptoms: Fatigue, weightloss, fever.

Hystologic features: Composed of Scattered cells within mucupolusaccharide stroma or stellated mesenchymal cells within myxoid background w/ inflamation and endothelial cells.

A/w the production of Vascular Endothelial Growth factor (VEGF) which contributes to angiogenesis and is the cause of abnormal blood vessels and hemorrhaging often seen.

Can produce Mitral Stenosis by the ball-valve effect: Flop over and cause an Early diastolic sound-" Tumor Flop".

Source FA, Cardio, UWqbank

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#2951322

ae0704 - 09/15/13 15:29 Q:7

Answer: B

Horner's Syndrome: Triad: 1- Ptosis 2-Miosis 3- Anhidrosis+ Flushing. A/w:

-Lesion of the spinal cord above T1 -Pancoast Tumor

-Brown-sequard

-Late stage syringomelia

-Bronchogenic Carcinoma of Apex (Lung)

Either of these lesions can affect the Superior Sympathetic Cervical Ganglion by tumor invasion of these autonomic ganglia and brachial plexus..

Source: FA Neuro.

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#2951333

ae0704 - 09/15/13 15:37 Q:8

Answer: B

Femoral Neck Fracture:

The Neck of femur is supply by the medial femoral circumflex artery arises from the medial and posterior aspect of the deep femoral artery (also known as profunda femoris artery, branch of femoral artery), and winds around the medial side of the femur, passing first between the pectineus and iliopsoas muscles, and then between the obturator externus and the adductor brevis muscles. The medial femoral circumflex artery may occasionally arise directly from the femoral artery. Injury to this vessel can cause avascular necrosis of femoral head.

Source: wikipedia

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#2951337

sdfghjk - 09/15/13 15:49

It would be helpful if you could also post the questions.... as the question number does not mean anything...

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#2951343

ae0704 - 09/15/13 15:55 Q:9

Answer: C

Zollinger-Ellison Syndrome:

Gastrin-secreting tumor of pancreas, duodenum or lymph nodes.

This increase in the production of gastrin result in the stimulation and trophic proliferation of parietal cell which in turn increases the secretion of Gastric acid leading to the formation of recurrent ulcers, mc duodenal.

Presents: Abdominal pain, acid reflux, and sometimes diarrhea (a response of the acidified duodenum, increases secretin causing secretory diarrhea).

Can be part of MEN type I.

Treatment: -PPis ( Moa: H-K-ATPase inhibitors) -Octeotride (somatostatin analog).

The most simple and reliable test for ZES is Secretin Injection, which normally will inhibit Antral gastrin secretion, but stimulates gastrin secretion in patients w/ ZES.

Source: FA GI, Kaplanqbank, UWqbank.

#2951346

ae0704 - 09/15/13 16:01

Hello @sdfghjk, since there's a warning w/ copyright material in this forum, im not posting the questions stems, but as i hinted above, i am following the order from the one posted in SCRIBD by user StepPrep.

Please look for them there, and help yourself w/ some explanations here. Thank you.

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#2951362

ae0704 - 09/15/13 16:24 Q:10

Answer: D

Spherocytosis: Intrinsic hemolytic normocytic anemia, caused by a defect in proteins interacting with RBC membrane skeleton and plasma membrane (Ankyrin, band.3.1 or spectrin). Autosommal Dominant.

Pathogenesis: Less membrane=decrease membrane causes small and round RBC w/ no central pallor (Spherocytes) -->this is appreciated in the labs w/ the ↑ MCHC and RDW (indicates membrane loss and cell dehydration).

This leads to premature removal of RBC by spleen (Characteristic accelerated RBC destruction). Presentation: Anemia, jaundice, splenomegaly (Due to RBC sequestration).

Labs:Positive (+) Osmotic Fragility test, ↑ MCHC, RDW, Indirect bilirrubin and LDH. ↓ Haptoglobin

Smear: Spherocytes and Howell-Jolly body after splenectomy.

Assoc/ increase risk of Aplastic crisis (parvovirus b9 infx) and pigmented gallstones (bilirrubin gallstones) **prevent w/ splenectomy.

Source: FA hemato.

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#2951366

ae0704 - 09/15/13 16:29 Q:11

Answer: B

Vinblastine: MoA: Alkaloid that binds to tubulin in M phase and block Polymerization= Assembly of microtubules so that mitotic spindle cannot form.

Uses: Hodgkin L, Wilms tumor, Choriocarcinoma, ALL. Tox: Bone marrow suppression.

Source: FA, Hemato.

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#2951378

ae0704 - 09/15/13 16:49

Q: 12 : "Insulin Slope in myocytes" Answer:B

Insulin-responsive: GLUT-4, required for Adipose, skeletal muscle in order to uptake glucose. The Y axis is the rate in which glucose is uptake by myocyte,

Since the stem depict that the solid line correspond the absence of insulin, none of the glucose is going to be uptake reason why we see the flat slope on the x axis, describing that there wasn't an uptake. and in the presence of insulin (dashed lines) the rate of uptake increases showing that when there's increases in insulin, GLUT-4 in those tissues, began to uptake glucose inside in bigger rate.

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#2951383

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Q: 13 Answer: A.

Asperger Disorder: Milder form of Autism, Characterized by All-Absorbing interests, repetitive behavior and problems with social relationships.

Childrens are of normal intelligence and lack verbal or cognitive deficits. No language impairment. Source: FA pysch.

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#2951385

ae0704 - 09/15/13 17:05 Q:14

Answer: F

Number Needed to treat (NNT)---->NNT=1/ARR (1)ARR=Exposed-Unexposed

Assuming Trace elements as Control or Exposed:2.3% or 0.023 Unexposed: 1.3% or 0.013

ARR=0.023-0.013=0.01 (2)NNT=1/0.01= 100.

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#2951392

ae0704 - 09/15/13 17:10 Q:15

Answer: E Herpes labialis:

HSV-1: dss-DNA enveloped icosahedral.

Causes gingivostomatitis, keratoconjuctivits, temporal lobe encephalitis, Herpes labialis. transmitted by respiratory secretions.

Hides in the NEURONS of Trigeminal ganglia. Source: FA micro.

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#2951410

ae0704 - 09/15/13 17:29 Q:16

Answer: B

in Anemia theres a Decrease in Hb, Hct or RBC concetration. SaO2 (oxygen saturation) and PaO2 are Normal.

Decrease Oxygen Content (O2content).

Please, clarify, not sure about the reason this is the answer, it was a lucky guess.

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#2951421

ae0704 - 09/15/13 17:41 Q:17

Answer: A

Hepatitis B recombinant Vaccine: When the 2nd dose is given, sensitized cells from previous exposure (first dose) got stimulated and now secrete IgG. So there will be an increase of IgG:IgM ratio since

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immune system already recognize the antigen. The IgG peak will occur earlier because of memory cells.

An excellent example given by: @zen786

"an animal was injected with Antigen A at day 0. Antigen A invokes a primary response beginning about day 4, as indicated by a rise in the specific antibody titer (titer = measure of the amount of antibody in the animal's serum per unit volume). Initially, this antibody is mostly IgM (and some IgG). After a peak titer between days 7 and 10, the response decreases rapidly. If the animal is then reinjected with Antigen A at day 28, the production of antibody begins almost immediately and reaches a level 1000-fold greater that that seen in the primary response. This is known as the secondary response and the principal antibody produced is IgG. If a second antigen (Antigen B) is also injected at the same time as the reinjection of Antigen A, however, only a primary response to Antigen B is observed. These results demonstrate that:

The immune response is specific and that the immune response has memory.

immunoglobulin always primary at presentation of an antigen is IgM.... secondary thats produced is always IgG unless mucuosal effected [IgA] or parastic infection [IgE].

IgG production will not be peaked in relation to IgM primarily.

but after a second reinfection IgG will peak faster hence MEMORY*** of immunoglobulin...

IgM will be present but not likely in elevated state due to memory of b cell releasing IgG right away... Later peak would not occur in a reinfection state.... LATER PEAK OF IgG can only be seen in a PRIMARY infection ... as you would see a later peak of IgG in "antigen B" exposure in the example above...."

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#2951423

ae0704 - 09/15/13 17:46 Q:18

Answer: D CO Poisoning:

produced by incomplete combustion of carbon containing compounds. causes: Automobile exhaust, smoke inhalation, wood stoves, methylene chloride (paint thinner).

Pathogenesis:

CO competes w/ O2 binding site on HB there by decreasing the Oxygen Saturation (SaO2) without affecting PaO2. Inhibits cytochrome oxidase in Electron transport chain (ETC) and causes a Left shift of Oxygen Binding curve.

Manifest w/ cherry red discoloration of skin and blood, headache (first symptom), dyspnea, dizziness, seizures and coma.

Tx: O2-nonbreather mask or endotracheal tube.

#2951426

ae0704 - 09/15/13 17:55 Q:19

Answer: A

Parietal Cell destruction: Leads to chronic Gastritis and Pernicious anemia due to decrease in Intrinsic Factor (Vit B12 binding protein)---Required for B12 uptake in Ileum.

Source: FA GI

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#2951427

ae0704 - 09/15/13 17:55 Q:20

Answer: A

Exogenous use of levothyroxine

Commonly used iatrogenically to weightloss, can be seen in the labs:

characterized by an increase of Serum T4 and Free T4, Decrease TSH and Deacrease 123Iuptake. Source: Goljan

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#2951438 ae0704 - 09/15/13 18:13 Q:21 Answer: A Klinefelter: Diagnosis: Labs: ↓ Inhibin-->↑FSH ↓Testosterone---> ↑LH--->↑estrogen Spermcount: Azoospermia

Testicular Biopsy: Seminiferus tubular sclerosis/dysgenesis

Barr bodies analysis (seen on neutrophils), Karyotyping of Lymphocytes

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#2951445

ae0704 - 09/15/13 18:17 Q:22

Answer: A

Since shes have been not eaten well since she began taking care of her mother before passing i assume she developed an involuntary Anorexia Nervosa: As % of body fat decreases the Normal cyclic LH surge lost and hypogonadotropic amenorrhea develops.

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#2951448

ae0704 - 09/15/13 18:20 Q:23

Answer: A

Tiotropium, Ipratropium: Muscarinic antogonist--> Block Ach action at parasympathetic sites in bronchial smooth muscle, use in Asthma and COPD.

Source: FA Pharm

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#2951453

ae0704 - 09/15/13 18:22 Q:24

Answer: E

Pheocromocytoma- derived from Chromaffin cell (Arise from Neural crest cell) Source: FA Endocrine

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#2951463 ae0704 - 09/15/13 18:31 Q:25 Answer: A **Need explanation Report Abuse

#2951475

ae0704 - 09/15/13 19:04 Q:26

Answer: C

MHC I-nucleated cells infected w/ virus Source: FA Immuno

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#2951479

ae0704 - 09/15/13 19:10 Q:27

Answer: E

Metabolic acidosis compensation, Hyperventilation seen on pte. PCO2 of 13 also Kidney will get rid of acid..

**Please Add more information

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#2951481

ae0704 - 09/15/13 19:15 Q:28

Answer: C

Diverticulitis: Inflamx of diverticula classically causing LLQ pain, fever, leukocytosis. May perforate and produces peritonitis, abscess formation or bowel stenosis.

May cause rectal bleeding, also colovesical fistula-pneumaturia. Tx: Non-pharmacologic; encourage water intake and high fiber diet Give ABX: Outptes: Metro +TMP-SMX +Levo/cipro.

#2951482 ae0704 - 09/15/13 19:18 Q:29 Answer: A? **Need explanation Report Abuse

#2951484

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Q:30 Answer: C

Long Thoracic Nerve injury results in paralysis of Serratus anterior muscle and inability to aBduct shoulder past 90 degree/weakness in the ability to potract the scapula-Winged Scapula.

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#2951485

ae0704 - 09/15/13 19:23 Q:31

Answer: A

Septic Arthritis: Gonococcal Arthritis due tu N. Gonorrhae, presents as a monoarticular migratory arthritis w/ an assymetrical pattern. Affected joint is swollen, red, and painful.

Dgx: Synovial fluid: WBC>20,000/mm Tx: Ceftriaxone

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#2951486

ae0704 - 09/15/13 19:25 Q:32

Answer: F

BCL-2 is an oncogen which function is to inhibit apoptosis, the more bcl-2 the more cancer cells that wont go through apoptosis.

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#2951487

ae0704 - 09/15/13 19:26 Q:33

Answer:

****Waiting for Answer and Explanation***

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#2951489

ae0704 - 09/15/13 19:29 Q:34

Answer: B

Infliximab: TNF alpha inhibitor. Tox: Respiratory infection (Reactivation of TB)

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#2951491

ae0704 - 09/15/13 19:31 Q:35

Answer: C

Foreign body aspiration,

Hints: the decrease of air movement on the right (Mc site of aspiration), the sudden onset of the scenario.

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#2951493

ae0704 - 09/15/13 19:33 Q:36

Answer: E

Transplanted patient hence immunosuppressed-- decrease lymphocytes-- CMV pneumonitis.

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#2951494

ae0704 - 09/15/13 19:35 Q:37

Answer:A

Decrease in MAP activates Sympathetic activity: 1) B1--> increase HR, Contractility and C.O. 2)Alpha1--Venoconstriction--Increase in C.O and Arteriolar constriction--Increase TPR.

The patient probably has splenic rupture. The venous side of the circulation would constrict

in an attempt to increase preload. All that sympathetic stimulation (alpha and beta) would

constrict arterioles and venules in an effort to raise BP, and HR would raise as well.

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#2951495

ae0704 - 09/15/13 19:37 Q:38

Answer: D recommend further evaluation to determine the cause of the patient’s language delay Autism: Language impairment, poor social interaction, focus on objects, dont make eye contact, absent social smile, mc age diagnosed age 3.

#2951496

ae0704 - 09/15/13 19:39 Q:39

Answer: A

N meningitidis: Polysaccharide Capsule, Vaccine contains Antibodies against it.

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#2951497

ae0704 - 09/15/13 19:42 Q:40

Answer: D

Angiotensin Converting Enzyme (ACE) is formed on pulmonary vasculature.

Since the reason for this pte. HTA is mediated by a vasoconstrictor, in this case Angiotensin II (AII). AII arise from AI via ACE.

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ae0704 - 09/15/13 19:45 Q:41

Answer:D

Ribavirin: Inhibits guanine nucleotide by competitively inhibiting IMP dehydrogenase/ Interfere w/ duplication of viral genetic material.

Clinical use: previously RSV, Chronic Hep C Tox: hemolytic anemia, severe teratogen

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#2951499

ae0704 - 09/15/13 19:47 Q:42

Answer:E

Subluxation of radial head: MC in children due to sharp pull of hand while forearm is pronated and elbow extended, sudden traction, leading to annular ligament tear--presents weak pronated arm close to body.

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#2951501

ae0704 - 09/15/13 19:50 Q43:

Answer: D

Portal Hypertension:

Short Gastric, arise form Splenic vein, part of portal system.

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#2951502

ae0704 - 09/15/13 19:52 Q:44

Answer: C

Nitroglycerine, Venodilator, increase cGMP synthesis. Decreases preload and increase coronary blood flow.

Use in angina in lower doses.

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#2951504

ae0704 - 09/15/13 19:54 Q:45

Answer: C

Alzheimer: Decrease Ach in nucleus basalis of meynert and hippocampus.

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#2951505

ae0704 - 09/15/13 19:57 Q:46

Answer: C

Xeroderma Pigmentosum: Nucleotide excision repair defect, specific excision endonuclease, prevents the repair of thymidine dimers form from uv light exposure. AR, dry skin w/ melanoma and other cancers.

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#2951506

ae0704 - 09/15/13 20:01 Q:47

Answer: E

Nephrogenic Diabetes insipidus: can be heriditary as in this case, a v2 rc deficiency or 2dary to drugs and hypercalcemia.

Lack of response to ADH.

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#2951508

ae0704 - 09/15/13 20:05 Q:48

Answer: G

Anterior Horn lesion---Lower Motor neuron (LMN) : Ipsilateral side after decussation.

LMN signs: Weakness, Atrophy, Fasciculations, Decreases reflexes (arreflexia), Flaccid paralysis.. **atrophy of intrinsic muscles of hand, commonly is the first sign in ALS.

#2951510

ae0704 - 09/15/13 20:08 Q:49

Answer: D

Leiomyoma: Multiple tumors w/ well demarcated borders. Increase incidence in blacks. Benign smooth muscle tumor. Estrogen sensitive, Increase w/ pregnancy and decrease w/ menopause. maybe

asymptomatic or present w/ bleeding or result in miscarriage. Severe bleeding may lead to iron deficiency anemia, Histo: WHorled pattern muscle bundles, actin positive. treatment Leuprolide or hysterectomy.

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#2951511

ae0704 - 09/15/13 20:10 Q:50

Answer: F nuclear receptors

Receptors for several steroid Rc hormones such as corticosteroids, mineralocorticoid, androgen, estrogen usually present initially at cytoplasm although they migrate to nucleus once activated.

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#2951803

ae0704 - 09/16/13 07:28 ** Addition to Q16 **

Answer: B: Arterial O2-carrying capacity -Anemia

findings-in Anemia there's a Decrease ↓ findings-in Hb, Hct or RBC concentration. SaO2 (oxygen saturation) and PaO2 are Normal.

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Oxygen Content is defined as the total amount of O2 carried in blood--->Oxygen carrying capacity (Option B in question stem).

*O2 content= (Hb (g/dl) x 1.34) x SaO2 + PaO2 x 0.003

Hemoglobin concentration (Hb) in RBC is the most important factor and important carrier of oxygen, HB concentration determines the total amount of oxygen (O2) delivered to tissue.

Anemia, decrease in HB concentration , with this reduction there will be a decrease in oxygen carrying capacity of blood, leading to a decrease O2 delivery to tissue--> Hypoxia.

Anaemic hypoxia is most frequently attributable to a low Hb. Source: goljan and additional info via @shells, my250, ale333.

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#2951808

ae0704 - 09/16/13 08:02

**Addition to Q29: km & Vmax**

Answer: A: The Km cannot be predicted based solely on value of Vmax.

The Km is the substrate concentration at 1/2 Vmax. So basically it is just a constant to allow the researcher, to analyze the affinity of an enzyme or reaction. Since you need both the Y and X axis'es in order to have a slope you will need the substrate concentrations in order to determine Vmax.

http://upload.wikimedia.org/wikipedia/commons/9/99/Michaelis-Menten_saturatio...eaction.svg Example: Hexokinase may have a Vmax of 200, whereas Fructokinase may have the same Vmax (for whatever reason, due to saturation, structural similarities, etc.) but they could very well (and I don't know if this is the case, just an example) have very different affinities and therefore a very different slope of the curve. Imagine if it was nearly a linear slope vs. another one which is a lot less rise/run --both can still have the same plateau.

via @nkhan

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* **q25**

#2951919

usmlevaccine - 09/16/13 10:51

The patient has prostatic adenocarcinoma, common in men > 50 years of age. He has weight loss, inc in PSA, hard mass in the prostate and it metastasized to vertebral bodies. The most appropriate treatment is Leuprolide-GnRH analog with antagonist properties when used in continuous fashion (with flutamide-androgen receptor inhibitor); agonist when used in pulsatile fashion (used in infertility).

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#2952015

ae0704 - 09/16/13 12:15

Thank you so much @usmlevaccine, i wasn't sure, that the true mechanism of leuprolide was to activate GnRH receptors since in FA says "GnRH analogs" only.

***Q25, Answer: A ***** Confirmed.

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#2952096

usmlevaccine - 09/16/13 13:25

No problem! I'm actually glad that you are posting answers and explanations. I did NBME 12 recently and was looking for explanations. Couldn't just rely on scribd.

Leuprolide can be used as an agonist or antagonist.

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If it's used in continuous fashion --> it worsk as an antagonist --> used for prostate cancer

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#2952138

usmlevaccine - 09/16/13 13:55 **Addition to Q 27**

Patient is having metabolic acidosis with respiratory alkalosis compensation. Kidney should be excreting acid as well.

A- decreased H+ secretion in the tubule --> should be inc

B- decreased proximal tubule HCO3- reabsorption -->proximal tubule normally reabsorbs most of bicarbonate, sodium chloride, and water

C- decreased titrable acid excretion --> should be inc D- increased HCO3- excretion --> should be dec E- increased NH4Cl excretion --> correct

Intercalated cells of collecting ducts can make brand new HCO3- and secrete H+ into the lumen and makes urine acidic.

H2O + CO2 --(carbonic anhydrase)--> H + HCO3