Explanations for the 2016 Official Step 1 Practice Questions

The NBME has released the new 2016 “USMLE Step 1 Sample Test Questions,” which reflect a sizable decrease in the number of questions from 308 down to 280 and now 40 questions per block after May 9th, 2016. Exam duration is unchanged, so this should help those who have difficulty with time management/finishing sections on time.

Additionally, on the software package, you can now invert the colors for white text on a black background. If that’s your thing.

You’ll remember from last year that there weren’t any new questions. This year there are 49 new ones (marked with asterisks).

The questions and explanations for last year (2014/2015) can still be found here.

Block 1

1. D – ITP causes immune-mediated consumption of platelets, hence the low platelet count and petechiae. The bone marrow biopsy results demonstrate that the body has appropriately increased platelet production, meaning that this is not a platelet production issue. While TTP has a similar acronym, it’s an entirely different disease with a classic pentad: thrombocytopenia (low platelet count), microangiopathic hemolytic anemia, altered mental status, renal failure, and fever.
2. A – Crystal disease of the knee is mostly commonly pseudogout (aka calcium pyrophosphate deposition disease / CPPD). Contrast with gout which most commonly first affects the great toe MTP. These crystals would be positively birefringent (not mentioned). The radiographic features are microdetails that are unlikely to make or break the diagnosis on your test.*
3. A – Targetoid rash after a woodland excursion means Lyme disease, caused by Borrelia burgdorferi, carried by the Ixodes tick. Rash (erythema migrans), viral syndrome symptoms, fatigue, and polyarthritis are common. Lyme carditis typically manifests as AV block.
4. D – Of the choices, only Shigella is a common US pathogen causing dysentery (bloody diarrhea). Shigella is extremely virulent, and a handful of organisms is enough to cause infection, with the misery-inducing Shiga toxin being similar to the toxin produced by enterohemorrhagic E coli’s O157:H7 strain that can result in hemolytic uremic syndrome.*
5. B – Alcoholics (and any person with an altered level of consciousness) are a set-up for aspiration pneumonia: classically RLL, classically foul-smelling. The organism on tests will be Klebsiella.
6. A – A new blistering disease in an older person is typically going to be a pemphigus question. Then you just have to remember the difference between bullous pemphigoid vs pemphigus vulgaris. Bullous pemphigoid is characterized by the loss of hemidesmosomes that bind keratinocytes to the basement membrane, resulting in bulla (big blisters) in areas of friction, choice A. Patients with pemphigus vulgaris lose their desmosomes (which bind keratinocytes to each other), so that their skin is super friable, which results in ulceration. Mouth ulcers are more common in PV.
7. C – A history of volume loss (often GI 2/2 vomiting, diarrhea) resulting in shock is consistent with a hypovolemic etiology, as corroborated by the plethora of physical evidence provided. Diuretics exacerbate the situation, working against your body’s desire to retain fluid to compensate.*
8. B – This patient has cystic fibrosis. The combination of respiratory and GI issues is classic and caused by ineffective chloride transport and consequently thick exocrine secretions, which clog up the airways and the pancreatic ducts.
9. G – Great example of a long-winded set up for a heart attack followed by the giveaway diagnosis of heart attack (*cue moan for wasted time*). Beta blockers are given to reduce myocardial oxygen demand and thus reduce ischemia by slowing the heart rate and reducing contractility.*
10. C – Filgrastim is a granulocyte colony stimulating factor (GCSF), which are drugs used to increase white blood cell count in patients with leukopenia. Leucovorin (folinic acid) sounds like it would also be right, but it’s used to prevent bone marrow suppression in patients taking methotrexate. Darbepoetin (like erythropoietin) is used to stimulate red blood cell production.
11. B – To amplify tiny fragments of DNA in order to detect their presence, we use PCR. The question is a description of the process. Southern Blots are used to detect a specific DNA sequence within a DNA sample.
12. C – This is obviously a clinical trial. If you know you are getting a drug, then you are not blinded: it’s an open-label trial. There is no randomization as there is only a single treatment group.
13. C – Osgood-Schlatter is also known as apophysitis of the tibial tubercle. It’s due to chronic stress/irritation at the insertion of the patellar tendon on the tibial tubercle. It’s classically seen in teenagers doing repetitive vigorous activity (running, jumping). The radiograph demonstrates classic fragmentation of the tibial tubercle (which isn’t necessary to know to get the question correct).
14. D – If the patient was positive for HIV, then the wife must be informed. In the absence of the disease-related exposure, this is none of your business. Private health information is private.*
15. B – The arrow is pointing to a neutrophil (multilobed nucleus): main fighter of the immune system in acute inflammation and bacterial infection (such as aspiration pneumonia). C5a is a chemotactic factor for PMNs.
16. B – Isoniazid is hepatotoxic and can cause serious liver damage. Highly testable. It can also cause drug-induced lupus (which is probably even more testable).*
17. B – Albuterol (inhaled short-acting beta2-agonist) is the treatment of choice for wheezing/reactive airways/bronchospasm/asthma. Note that timolol is a beta-blocker and beta-blockers can cause bronchospasm/exacerbate asthma. Even eye drops.*
18. A – Electrical alternans on boards means a big pericardial effusion (and usually cardiac tamponade physiology). The heart cannot fill properly, preload decreases, hypotension and tachycardia ensue, fluid backup leads to elevated JVP. Underlying etiology in this patient is renal failure.
19. C – If you don’t eat enough calories to run your metabolism, your body will mobilize its stores. We “burn” fat through fatty acid oxidation.
20. A – Ah, countertransference. Remember that transference is when the patient is transferring (redirecting) feelings about someone on to you (you remind them of their dad). Countertransference is when you do it about them (they remind you of your son). Projection is when you assign your own feelings to them (you are angry, so you think you they are angry).*
21. A – Gonorrhea can change its pilus, which is responsible for adhesion to host cells and the main antigen to which the host mounts an immune response. Neisseria gonorrhoeae is able to switch out different pilin genes, and for this reason, prior infection does not confer long-lasting immunity.
22. E – The whole afferent/efferent thing is worth knowing. When the efferent arteriole is independently constricted, the blood can get into the glomerulus but has difficulty getting out. So more blood spends a greater amount of time in the glomerulus being filtered: GFR up, filtration fraction up, but overall blood flow is decreased due to the increased resistance of the system as a whole.
23. E – DMD is X-linked. We know her mom is a carrier based on family history, supported by lab testing. But her mom has 2 X chromosomes, only one of which is mutated. There is no way to know which her daughter eventually receives and expresses by her phenotype (i.e if she is a carrier or not). Just because her CK is normal doesn’t mean she isn’t a carrier–the phenotype of the X-linked carrier depends on X-inactivation.*
24. A – The infraspinatus and teres minor are responsible for external rotation. Both the infraspinatus and supraspinatus muscles are innervated by a suprascapular nerve.
25. B – Type I hypersensitivities aka “allergies” (as seen in snot, hives, and eyes) are mediated by IgE (mast cells, basophils).*
26. D – The baroreceptors are stretch receptors (the more fluid in the vessel, the more they fire). So a patient with hemorrhagic shock will see a decrease in the baroreceptor firing rate. Activation of RAAS will result in increased vascular resistance (vasoconstriction) in order to maintain blood pressure. And capillaries, such as those in the kidney, will be primed for resorption and not filtration (no one wants to pee out good dilute urine when they’re dehydrated). Likewise, systemic capillaries will prefer to hold onto plasma and not let it leak into the interstitium (third-spacing).
27. A – GBS comes from a mother’s colonized vagina and is the most common cause of neonatal sepsis. Women who are GBS+ should receive PCN prophylaxis prior to vaginal delivery to prevent exposure to the fetus on the way out.
28. C – Just because he’s having (unprotected) sex doesn’t mean he doesn’t have simple infectious mononucleosis. The sex implies he’s also kissing someone! Pharyngitis + lymph nodes + fatigue = mono.*
29. B – You want this to be a CYP450 question but it’s not. Some drugs require an acidic environment to be satisfactorily broken down or dissolved for GI absorption. Omeprazole raises gastric pH and reduces GI absorption.*
30. A – All the vesicles contain the same viral infection, so all should have the same appearance on gel. Choice D is what a gel looks like without using a restriction enzyme digest (no discrete bands of specific weights).
31. C – Effects of PTH – Raise calcium and vitamin with an overall decrease in phosphorous (due to decreased urinary resorption).*
32. B – Juxtaglumerular cells secrete renin when their beta-1 receptors are stimulated. Blocking the JGA reduces everything in the cascade, including renin. Blocking anything later in the RAAS pathway would cause an elevation in renin as an attempted compensation.*
33. D – Knowledge of the normal cavernous sinus contents and all of the cranial nerves and their functions is low-hanging fruit. Ocular ABduction is mediated by the ABducens nerve, CN VI.
34. D – Losartan is an angiotensin II receptor antagonist used to treat hypertension by blocking the effects of angiotensin II and reducing aldosterone production. Vessels relax, sodium is less held onto, which results in decreased blood pressure via the decrease in the peripheral resistance and preload.*
35. C – This patient has hepatitis (elevated liver enzymes) due to active Hepatitis C infection. Hep C and HIV infection are both associated with intravenous drug use. While most patients with Hep A will clear the virus after their acute illness, Hep C causes chronic infection in 80% of patients, which may lead to cirrhosis over time (~20 years).
36. B – Bisphosphonates work by decreasing osteoclast activity (thereby reducing bone resorption). Choice F is the opposite of how estrogen therapy works (RANKL is found on osteoblasts, and its activation triggers osteoclasts and stimulates bone resorption).
37. D – Relationship with former patients are generally frowned on, but they’re especially problematic if the patient was a psychiatric patient, as the power imbalance of the practitioner-patient relationship and information the provider is privy to because of their patient care involvement preclude a healthy balanced relationship of equals.*
38. B – Memorize aspirin’s acid-base effects: metabolic acidosis and respiratory alkalosis. Note, this is actual respiratory alkalosis, not simply normal respiratory compensation for metabolic acidosis.
39. C – Most “biologics” are monoclonal antibodies. Infliximab (remicade) and adalimumab (humira) for example both block TNF-alpha and are both antibodies (end in “mab” for monoclonal antibody). As such, the body can eventually form an immune response to the foreign protein.*
40. A – As always, it’s almost better to ignore the pictures when possible. This gentleman has a peptic ulcer, which we know is caused predominately by H. pylori infection. H. pylori produces proteases and particularly urease, which allow it to increase the pH of its local environment by cleaving urea into ammonia, which is toxic to gastric mucosa. The picture demonstrates H pylori, which are evident with silver staining.

Block 2

41. D – Sensitivity rules things out. It’s TP / (TP + FN). So in order to calculate the sensitivity of this test, we need the true positives (the 90 with cancer) and the false negatives: the patients for whom the test is negative but actually do have prostate cancer. That’s D.
42. D – Those are varicose veins, and they’ve described symptomatic varicosities. Incompetent valves allow reflux of blood into the dependent feet and legs. The pooling blood increases hydrostatic pressure, causing edema.
43. F – This question is so easy it almost defies logic. Treatment of choice is pyrimethamine+sulfadiazine (and folate). Unlikely to be tested, but the differential for a ring-enhancing lesion in an AIDS patient is CNS lymphoma (which is more likely to be solitary). In real life, one can do a thallium or PET scan to distinguish the two (lymphoma, being cancer, is metabolically active; the toxoplasma abscess is not).*
44. E – Kidneys hold onto salt and fluid in the event of volume loss.* Vasoconstriction certainly occurs to maintain blood pressure, and while this is related to RAAS, this is not the “best” answer, because the kidneys aren’t doing the constricting; the vasculature is.*
45. B – p53 is an important tumor suppressor gene, particularly in its ability to cause a cell to undergo apoptosis in the event of damage. p53 activity also holds the cell at the G1/S regulation point (B), limiting DNA synthesis.*
46. C – Swallowing amniotic fluid is a critical component of lung development. Fetuses with severe oligohydramnios are plagued by pulmonary hypoplasia, which is the cause of death in fetuses born with Potter syndrome (renal agenesis).*
47. D – The arrowed fluid is contained in a space behind the stomach but in front of the retroperitoneal structures (e.g. the pancreas), i.e. the lesser sac.
48. B – The vast majority of pancreatic cancers arise from the ductal epithelium (>80%), possibly due to long-term exposure to lots of potent secretions. Acinar epithelium is responsible making exocrine secretions. Islet cells can form neuroendocrine tumors (insulinomas).*
49. A – Turner syndrome (you may remember lymphedema of the neck by another name: cystic hygroma). The 45,X gives it away though anyway. Mosaic Turner’s syndrome and the mosaic trisomies result from nondisjunction during mitosis. In total monosomy/trisomies, the cause is nondisjunction during meiosis. Uniparental disomy is essentially only tested via the Prader-Willi and Angelman syndromes (chromosome 15).
50. C – Statins raise HDL and decrease LDL and TGs. Their effect on LDL is by far the most potent, but they do a little good on everything.*
51. C – Lymphatic spread of disease moves through lymphatic channels from distal to proximal. The medial side drains to the superficial inguinal nodes. Much of the lateral side will stop at the popliteal nodes prior to ascending the thigh.
52. B – What we have here is a congenital intolerance to breast milk: galactosemia, in which the body cannot convert galactose to glucose (resulting in an accumulation of Galactose 1-phosphate). They then list the findings and tests used to diagnose it. Lactose (the disaccharide in milk) is composed of glucose + galactose.
53. F – The statin is saving 10 people per 1000. Good numbers for easy math. So we need to treat 100 people to save 1, at a cost of $1000 x 5 years per patient. 100 x $5000 = $500,000 (F).*
54. B – Crossed findings means a brainstem lesion. Left (ipsilateral) tongue, right-sided (contralateral) weakness means the exiting left hypoglossal nerve has been affected (within the left medulla). B is the pyramid where the corticospinal tract runs to control muscles (prior to the decussation). This is known as the medial medullary syndrome or Dejerine syndrome.
55. A – The alpha-value corresponds to the p-value we will accept as significant and reflects the likelihood of a type I error (a false positive). A lower alpha-value means a lower acceptable likelihood of obtaining the same results by chance, and thus, significant results can be reported more confidently (a 1% false positive rate instead of a 5% rate).
56. D – Adult polycystic kidney disease (APKD) is autosomal dominant. Thus 50% of their kids will get it.*
57. A – The closer R is to 1, the more closely the data points should fit to a line. I think the NBME is trying to imply that I will have poorly controlled diabetes in the future.
58. A – Pyknosis and nuclear fragmentation are part of the process of apoptosis.
59. A – An annular pancreas occurs when the pancreas is wrapped around the second (descending) portion of the duodenum. When symptomatic (in adults, typically when there is superimposed pancreatitis), it can block the flow of GI contents through the intestines.
60. D – Recurrent respiratory infections could be a lot of things. But then they mention the dextrocardia. Kartagener syndrome is the combination of situs inversus and defective cilia (due to a mutation in dynein), where the inability to effectively clear secretions results in recurrent sinusitis and bronchiectasis.
61. E – This patient has chronic kidney disease, as indicated by elevated serum creatinine/BUN and evidence of anemia of chronic disease (normochromic normocytic). Poorly functioning kidneys do not hydroxylate 25-Dihydroxycholecalciferol to 1,25-Dihydroxycholecalciferol well nor produce adequate erythropoietin (hence the CKD-related anemia). Patient’s with CKD development thus develop secondary hyperparathyroidism due to deranged phosphate excretion and inadequate Vitamin D activation resulting in hypocalcemia.  Thus, we should expect to see low calcium, high phosphorus, low 1,25 vitamin D, and low Epo, which is E.
62. E – Pubertal gynecomastia in males is normal and generally goes away on its own. If “normal” is an answer choice, make really sure you don’t want to pick it.*
63. C – Serum sickness! A type III (immune complex) hypersensitivity.*
64. E – Gram-positive rods in a diabetic foot wound (or a World War I soldier fighting in a trench) means Clostridium perfringens (the causative organism of gas gangrene). Crepitus means gas in the tissues, which is produced as a byproduct of its highly virulent alpha toxin.
65. E – Endothelial tight junctions’ permeability is increased in response to injury and inflammation, allowing migration of white blood cells and friends to the site of injury.
66. D – No B cells and their antibodies. No CD4 or CD8 T cells. So both limbs are out: SCID. DiGeorge syndrome also has missing T cells and no thymus, but B cells are present (though less effective without helper T cells).*
67. G – Vincristine (a mitosis inhibitor) frequently causes peripheral neuropathy, which can be severe and irreversible. Other fun associations are Bleomycin with pulmonary fibrosis, Cyclophosphamide and bladder cancer, and Doxorubicin with dilated cardiomyopathy.
68. D – The suprachiasmatic nucleus of the hypothalamus controls circadian rhythms. A few more key thalamic nuclei are worth knowing: Supraoptic releases vasopressin (ADH). The lateral nucleus controls thirst and hunger. The ventromedial controls satiety. Anterior controls temperature. The paraventricular nucleus releases CRH, TRH, and oxytocin.
69. A – Malonyl-CoA inhibits the rate-limiting step in the beta-oxidation of fatty acid. Logically, resting muscle requires less energy (and thus less need for fatty acid breakdown) than active muscle.
70. A – Narcotic use for acutely painful conditions is both reasonable and important. Short-term use (immediately post-surgical) does not lead to long-term dependence. And yes, drugs addicts should also receive narcotics to control pain.
71. C – Logic would dictate that a fracture of the inferior orbital wall through the infraorbital foramen might affect the infraorbital artery, and logic would be right.
72. B – Anorexia leads to hypogonadotropic hypogonadism, as the body realizes that the possibility of nourishing a fetus is zero and gives up the pretense. There’s a lot of supporting data, but one should guess this answer once you read the word “gymnast” (or “dancer”).*
73. C – The Pouch of Douglas is the space between the uterus and the rectum (i.e. the place where pelvic free fluid goes).*
74. B – Crohn’s: skip lesions, fistulae, strictures (and the unnecessary transmural involvement on histology).*
75. E – Splitting is an immature defense mechanism often employed by patients with borderline personality disorder. When splitting, a person fails to see others as capable of having both positive and negative qualities; at any given time, it’s all or nothing.
76. D – Antibiotic-associated diarrhea caused by clostridium difficile can be tenacious, difficult to treat, and even fatal. Alcohol-based rubs are not sufficient to kill the spores. Handwashing with soap is necessary, and equipment should be autoclaved to clean it.
77. E – Fragile X is a CGG trinucleotide repeat expansion disorder (which like Huntington’s is a test favorite). The maternal uncle is the hint to the X-linked inheritance. Austism-like behaviors and relatively large head are common; large testicles only appear after puberty.*
78. E – PCP is a sedative-hypnotic and dissociative anesthetic that generally acts as a downer but can also cause incredible aggression coupled with pain insensitivity (the superman drug). Vertical nystagmus is a commonly mentioned physical exam finding.*
79. C – He’s clearly in heart failure, so one wants to know his EF to determine between systolic versus diastolic and establish pretreatment baseline.*
80. D – Diffuse low-level ST elevation means pericarditis. These patients often complain of pleuritic chest pain, which is somewhat alleviated by sitting up and leaning forward, and have distant heart sounds. Common test causes include viruses, uremia, and 2-3 weeks after myocardial infarction (Dressler syndrome).

Block 3

81. E – von Willebrand disease is by far the most common inherited bleeding diathesis. Frequently, the only laboratory abnormality is increased bleeding time (literally you prick the patient and see how long it takes them to stop bleeding). On Step, bleeding women have VWD. Bleeding boys have hemophilia.*
82. C – Leydig cells make testosterone. Leydig cell tumors aren’t always physiological active, but those that are can cause masculinization. Granulosa cell tumors, on the other hand, sometimes produce estrogen (which can lead to precocious puberty in young girls but otherwise may be occult). Teratomas are oddballs that typically have fat, hair, teeth, etc. Thecomas will not be on your test. Ovarian carcinoid is highly unlikely to show up on your test, but if it did, it would likely present with a classic carcinoid syndrome.
83. B – Annular lesions with central clearing is a good appearance for Tinea corporis. Superficial fungal infections induce a T-helper response that results in class switching to IgE-producing B cells (mediated by IL-4), which can exacerbate atopic conditions.*
84. A – Pulmonary fibrosis (a restrictive pattern disease) is a major cause of mortality for patients with scleroderma. Logically, if the disease causes fibrosis elsewhere, it’s going to cause fibrosis in the lungs.*
85. A – Acetaminophen (Tylenol) can cause fulminant hepatic failure in overdose. This will probably be on your test.
86. D – An odds ratio greater than 1 signifies increases odds/risk/likelihood. If the 95% confidence interval range does not include 1, then the difference is statistically significant (though not necessarily clinically meaningful).
87. B – This is a (prospective) case series. There is no control group (and certainly no blinding).
88. C – If an adult is taking on behaviors common to children, it’s called regression (don’t feel bad if it’s something you might do yourself).
89. B – Thiazides (typically used as antihypertensives) also increase calcium resorption in the distal tubule and are therefore useful in preventing calcium oxalate stone formation in patients with hypercalciuria (the mechanism is not really worth learning). Thiazides block the Na-Cl symporter, as opposed to loop diuretics, which block the triporter, and acetazolamide, which blocks carbonic anhydrase in the proximal tubule.
90. D – SIADH is a test favorite a very common cause of hyponatremia (after dehydration). A variety of brain and lung pathologies are possible etiologies, with lung cancer (of any type) being an important cause.*
91. E – Androgens stimulate sebaceous glands and cause acne. In girls, this is primarily due to adrenarche (DHEA/DHEAS androgen production made by the adrenal gland the zona reticularis). Boys can also blame testosterone from gonadal puberty (pubarche).
92. A – Beta2-agonists like albuterol are the treatment of choice for acute asthma symptoms/exacerbations. This question is stupid.*
93. E – The patient’s chronic inflammatory pneumonitis is killing off his lung parenchyma (composed primarily of type I pneumocytes). Type II pneumocytes, in addition to making surfactant, can replicate in order to replace type I pneumocytes, so they will be increased. Chronic interstitial inflammation results in fibrosis, hence an increase in fibroblasts.
94. D – The “migratory serpiginous perianal rash” (ick) is classic for strongyloides, a parasitic roundworm acquired from larvae-contaminated soil. Strongyloides larvae can borrow (hence the rash) and can migrate to the GI tract and lay their eggs, which then hatch in the intestine and cause diarrhea. Treatment is Ivermectin (and if not, mebendazole/albendazole). Checking the stools for larvae is the most sensitive test. Parasite lifecycles are gross.*
95. E – Subacute combined degeneration (progressive peripheral sensory and motor loss) is a late sign of B12 deficiency, which is common in old people. On board exams, a geriatric patient who lives alone and may have a “tea and toast” diet is likely to have vitamin deficiencies, particularly of folate and B12.
96. A – Neutropenia most commonly predisposes to overwhelming bacterial infection. It may also be worth noting that patients with neutropenic fever must be covered with an antibiotic that covers for pseudomonas (e.g. pip-tazo, ceftazadime, or cefepime).*
97. D – The effects of excess thyroid hormone: attempted compensatory TSH suppression, increase in both T4 and free T4, and normal TBG. Note that the question doesn’t even hinge on TBG and is also unlikely to on the real thing.*
98. B – This question is a little bit BS, in that there is nothing in the stem at all to make you think this specifically. What the question is trying to ask is what factors cause malpractice suits in general. While professional competence is a cause, people love to discuss and the boards love to test about poor physician communication and lack of empathy as root causes.*
99. B – Note that the question is not asking what cells fight URIs. The question asks what lab finding would be consistent with decreased immune activity (and thus the only choice that matches “decreased” with an immune cell is the best answer). *
100. D – Schistosomiasis is a parasitic worm particularly endemic in Africa (Egypt in particular comes up a lot on questions) that is most associated with chronic cystitis. Calcifications of the bladder wall are essentially pathognomonic. Chronic infection is associated with an increased risk of squamous cell carcinoma of the bladder (as opposed to the usual urothelial/transitional cell).
101. C – Run of the mill neonatal jaundice is due to a build-up of indirect/unconjugated bilirubin and is essentially a physiologic finding in newborns due to the combination of fetal erythrocyte breakdown and transiently low hepatic excretory capacity. Particularly high or rapidly uptrending levels are treated with phototherapy due to the risk of kernicterus. Breastfeeding jaundice and breast milk jaundice are two additional etiologies of neonatal jaundice, both of which also result in indirect hyperbilirubinemia.*
102. A – Foot drop after compression in the lower leg = common fibular/peroneal nerve. Nerve compression syndrome = one reason why it’s important that casts not be too tight.
103. A – Air and fluid = hydropneumothorax. If that fluid is blood (s/p stabbing), it’s a hemopneumothorax. Lack of mediastinal shift indicates that it’s not under tension.
104. E – Calcium oxalate stones are the most common variety of kidney stones, but uric acid stones make up 5-10% as well. None of the other choices are associated with renal calculi of any variety.
105. A – Androgen insensitivity is caused by a defective androgen receptor. DHT is responsible for creating male genitalia during fetal sexual development. The default human gender is female. So a genetically male patient with complete androgen insensitivity is externally phenotypically female. Lack of response to adrenal androgens prevents hair formation during puberty (adrenarche).
106. G – Sulfonylurea medications (glipizide, glyburide) stimulate the pancreas to secrete more insulin. For this reason, they are most efficacious early in the disease process when pancreas still has remaining functional reserve.
107. E – Those are sickle cells on the smear. LUQ pain on test questions almost always means splenic pathology. All sickle cell kids will eventually infarct their spleen.
108. E – Functional parathyroid adenomas can cause elevated parathyroid hormone (PTH), which results in hypercalcemia and hypophosphatemia. Hypercalcemia is characterized by the rhyming symptoms of: stones (renal, biliary), bones (including bone pain to osteitis fibrosa cystica), groans (abdominal pain, n/v), thrones (polyuria, constipation), and psychiatric overtones (from depression to coma).
109. E – VEGF is a major tissue growth factor activated by injury, cytokine release (infection, inflammation) and hypoxia that promotes angiogenesis and also increases vascular permeability (hence the edema). This increased permeability aids in the movement of proteins and white blood cells to the site of injury.
110. B – The left-sided system is much higher pressure than the right side, hence the aortic valve closing is usually louder than the pulmonic valve. A P2 louder than A2 means that the pulmonary artery pressure is significantly elevated.
111. C –  Blood flow also increases during exercise. The more anaerobic metabolism you use and lactate build-up you have, the more hyperemia you need to clear out the waste products.
112. E –  Ventricular fibrillation is the most common cause of sudden cardiac death immediately after myocardial infarction. This is why we have AEDs all over the place now. Papillary muscle rupture classically occurs 2-7 days after an MI and results in massive life-threatening mitral regurgitation. Free ventricular wall rupture after an MI can result in cardiac tamponade.
113. C – RSV, like all respiratory viruses, spreads via respiratory droplet. Babies are too young to wheeze because of asthma; they wheeze because of RSV.
114. B – Head injury follow by the copious dilute urine means central diabetes insipidus. No ADH (made in the supraoptic nucleus of the hypothalamus, secreted from the posterior pituitary) means no aquaporin channels in the collecting ducts to resorb water.*
115. C – GVHD sucks. Skin and GI lesions are especially common sites (mucosal tissues are rapidly dividing and thus prone to attack).
116. A – p53 is the quintessential tumor suppressor (it activate apoptosis). Carcinogenesis of HPV is caused by insertion of the virus into the host DNA and producing a protein which binds to an essential p53 substrate, functionally inactivating the p53 and its apoptotic cascade. C (transactivation/TAX) is how HIV and HTLV cause cancer. E (cmyc translocation) causes Burkitt lymphoma.
117. F – The flexor surface rash is eczema. Pimecrolimus (like tacrolimus) is an immune-modulating drug that suppresses T-cell cytokine production.

Requests for further clarifications etc can be made in the comments below.

You may also enjoy some other entries in the USMLE Step 1 series:
— How to approach the USMLE Step 1
— How to approach NBME/USMLE questions
— How I read NBME/USMLE Questions
— Free USMLE Step 1 Questions