TheoryUSMLE Step 1 Medical Prep
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USMLE Step 1 Medical Prep exam — full Q&A walkthrough
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30 free USMLE Step 1 Medical Prep questions
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USMLE Step 1 Medical Prep
A newborn is noted to have low-set ears, micrognathia, and a cleft palate. The mother reports drinking alcohol daily during the first trimester. Which of the following best describes the embryologic period when these craniofacial abnormalities most likely developed?
Correct — D. Craniofacial abnormalities associated with fetal alcohol syndrome typically develop during the critical period of facial development in weeks 4-8 of gestation. This is when the facial prominences and palatal shelves form, and exposure to teratogens during this period can lead to dysmorphic features including low-set ears, micrognathia, and cleft palate. -
USMLE Step 1 Medical Prep
A 15-month-old child presents for a well-child visit. The parents are concerned because the child is not yet walking independently. Which of the following represents the appropriate developmental milestone for this age?
Correct — C. By 15 months of age, most children should be walking independently without support. This is a key gross motor milestone that typically occurs between 12-15 months. Children who have not achieved independent walking by 18 months warrant further developmental evaluation. -
USMLE Step 1 Medical Prep
A 30-year-old woman is 8 weeks pregnant and is prescribed isotretinoin for severe acne. Which of the following congenital malformations is most strongly associated with exposure to this medication during pregnancy?
Correct — B. Isotretinoin (a vitamin A derivative) is a potent teratogen that causes characteristic craniofacial abnormalities, including ear malformations, micrognathia, and cleft palate. It also causes cardiac and CNS defects. This medication is contraindicated during pregnancy due to its high risk of causing congenital malformations. -
USMLE Step 1 Medical Prep
A 24-week pregnant woman presents with vaginal bleeding and is diagnosed with placenta previa. Which of the following best explains how this condition affects maternal-fetal interaction?
Correct — A. Placenta previa occurs when the placenta implants over the internal cervical os, which can lead to maternal hemorrhage when the cervix begins to dilate. This condition interferes with maternal-fetal interaction by potentially compromising placental blood flow, which can lead to fetal hypoxia and growth restriction due to decreased nutrient and oxygen exchange. -
USMLE Step 1 Medical Prep
A 3-year-old child has difficulty interacting with peers, demonstrates repetitive behaviors, and has delayed language development. Genetic testing reveals a mutation affecting synaptic proteins. Which of the following best describes the gene-environment interaction in this condition?
Correct — D. Autism spectrum disorder often involves a complex interplay between genetic susceptibility and environmental factors. Genetic mutations affecting synaptic proteins can impact neural circuit development and connectivity, while early environmental exposures and experiences can influence how these genetic factors are expressed, potentially modifying the severity and presentation of the condition. -
USMLE Step 1 Medical Prep
During a pediatric visit, a mother reports that her 9-month-old infant becomes extremely distressed when she leaves the room, which was not the case a few months ago. This behavior most likely represents which normal developmental process?
Correct — C. Stranger anxiety and separation anxiety typically develop around 6-9 months of age as infants begin to form specific attachments to caregivers and can distinguish between familiar and unfamiliar people. This represents normal social-emotional development and coincides with the development of object permanence - the understanding that objects (and people) continue to exist even when they cannot be seen. -
USMLE Step 1 Medical Prep
A 42-year-old pregnant woman undergoes amniocentesis that reveals trisomy 21. Which of the following maternal factors most likely contributed to this chromosomal abnormality?
Correct — B. Advanced maternal age (typically defined as age 35 or older) is the most significant risk factor for trisomy 21 (Down syndrome). The risk increases exponentially with maternal age due to aging oocytes being more susceptible to nondisjunction during meiosis, which leads to trisomy 21 in the fetus. -
USMLE Step 1 Medical Prep
A newborn presents with ambiguous genitalia. Laboratory analysis reveals elevated 17-hydroxyprogesterone levels. During which week of embryonic development did the pathophysiologic process leading to this condition most likely begin?
Correct — A. Sexual differentiation of the external genitalia begins around week 7 of embryonic development. In congenital adrenal hyperplasia (suggested by elevated 17-hydroxyprogesterone), excessive androgen production during this critical period leads to virilization of female external genitalia, resulting in ambiguous genitalia. -
USMLE Step 1 Medical Prep
A premature infant born at 30 weeks gestation develops respiratory distress shortly after birth. Which of the following best explains the developmental basis for this condition?
Correct — D. Surfactant production by type II pneumocytes typically begins around weeks 22-24 but doesn't reach adequate levels until approximately 34-36 weeks gestation. Premature infants born before sufficient surfactant production are at high risk for respiratory distress syndrome due to poor alveolar stability, increased surface tension, and alveolar collapse, leading to impaired gas exchange. -
USMLE Step 1 Medical Prep
A 62-year-old man presents with crushing substernal chest pain radiating to the left arm that began while shoveling snow. ECG shows ST-segment elevation in leads II, III, and aVF. Which coronary artery is most likely occluded?
Correct — C. ST-segment elevation in leads II, III, and aVF indicates an inferior wall myocardial infarction, which typically results from occlusion of the right coronary artery (RCA). The RCA supplies the inferior wall of the left ventricle in approximately 80% of people (right-dominant circulation). -
USMLE Step 1 Medical Prep
Which chamber of the heart has the thickest myocardial wall?
Correct — B. The left ventricle has the thickest myocardial wall of all cardiac chambers, as it must generate sufficient pressure to pump blood throughout the systemic circulation against high resistance. The right ventricle has a thinner wall as it pumps against the lower-resistance pulmonary circulation. -
USMLE Step 1 Medical Prep
A 45-year-old female with a history of rheumatic fever presents with dyspnea on exertion. On auscultation, an opening snap followed by a low-pitched diastolic rumble is heard at the apex. Which valvular lesion is most likely present?
Correct — A. An opening snap followed by a low-pitched diastolic rumble at the apex is the classic auscultatory finding in mitral stenosis. This condition is often a sequela of rheumatic fever, which causes valve leaflet thickening, fusion of the commissures, and calcification that restricts blood flow from the left atrium to the left ventricle during diastole. -
USMLE Step 1 Medical Prep
Which of the following properly describes the sequence of events during the cardiac action potential of ventricular myocytes?
Correct — D. The cardiac action potential in ventricular myocytes follows this sequence: Phase 0 (rapid depolarization via sodium channels), Phase 1 (initial repolarization via potassium efflux), Phase 2 (plateau via balanced calcium influx and potassium efflux), Phase 3 (rapid repolarization via potassium efflux), and Phase 4 (resting membrane potential). -
USMLE Step 1 Medical Prep
A 58-year-old man with chronic atrial fibrillation is started on amiodarone. Which of the following adverse effects should be monitored most closely?
Correct — C. Amiodarone is associated with multiple adverse effects, but pulmonary toxicity (manifesting as interstitial pneumonitis or fibrosis) is one of the most serious and potentially life-threatening complications. Regular monitoring of pulmonary function and symptoms is essential for patients on amiodarone therapy. -
USMLE Step 1 Medical Prep
Cardiac output is calculated as the product of heart rate and which other parameter?
Correct — B. Cardiac output (CO) is calculated as the product of heart rate (HR) and stroke volume (SV): CO = HR × SV. Stroke volume is the amount of blood ejected by the ventricle during each contraction. -
USMLE Step 1 Medical Prep
A 72-year-old man with chronic angina is prescribed nitroglycerin. What is the primary mechanism of action of this medication?
Correct — A. Nitroglycerin is converted to nitric oxide, which activates guanylyl cyclase, increasing cGMP levels. This leads to smooth muscle relaxation and vasodilation, particularly in the venous circulation (reducing preload) and coronary arteries (increasing coronary blood flow), which relieves angina symptoms. -
USMLE Step 1 Medical Prep
A 50-year-old woman presents with exertional dyspnea and peripheral edema. Echocardiogram shows an ejection fraction of 60% with normal ventricular size but increased wall thickness. Left ventricular filling pressures are elevated. Which type of heart failure best describes this patient's condition?
Correct — D. This patient has features of heart failure with preserved ejection fraction (HFpEF), also known as diastolic heart failure. The normal ejection fraction (>50%) with increased wall thickness and elevated filling pressures indicates impaired ventricular relaxation and compliance, causing symptoms despite preserved systolic function. -
USMLE Step 1 Medical Prep
Which cardiac valve is located between the left atrium and left ventricle?
Correct — C. The mitral valve (bicuspid valve) is located between the left atrium and left ventricle. It has two leaflets (anterior and posterior) and prevents backflow of blood from the left ventricle to the left atrium during ventricular systole. -
USMLE Step 1 Medical Prep
A 65-year-old man with coronary artery disease presents with sudden onset of palpitations. ECG shows a regular narrow-complex tachycardia at a rate of 180 bpm with no visible P waves. Carotid sinus massage temporarily slows the rate. Which arrhythmia is most likely present?
Correct — B. This presentation is typical of atrioventricular nodal reentrant tachycardia (AVNRT), a type of supraventricular tachycardia characterized by a regular narrow-complex rhythm at rates of 150-250 bpm. P waves are often not visible as they are buried in the QRS complexes. AVNRT often responds to vagal maneuvers like carotid sinus massage, which temporarily slows AV nodal conduction. -
USMLE Step 1 Medical Prep
A 28-year-old male athlete has a loud, mid-systolic click followed by a late systolic murmur at the apex that intensifies with standing. Which cardiac condition is most likely?
Correct — A. A mid-systolic click followed by a late systolic murmur at the apex that intensifies with standing is characteristic of mitral valve prolapse. Standing decreases ventricular volume, causing earlier prolapse and intensification of the murmur. This condition is more common in young adults with lean body habitus. -
USMLE Step 1 Medical Prep
Which of the following accurately describes the function of cardiac troponin I?
Correct — D. Cardiac troponin I is a regulatory protein found in cardiac muscle that inhibits actin-myosin interactions in the absence of calcium. When calcium binds to troponin C, troponin I shifts position, allowing contraction to occur. Elevated levels in blood indicate cardiac muscle damage, making it a specific marker for myocardial injury. -
USMLE Step 1 Medical Prep
A 55-year-old man with hypertension and hyperlipidemia presents with acute chest pain. His ECG shows ST-segment depression in leads V1-V4. Which type of acute coronary syndrome is most likely?
Correct — C. ST-segment depression in the absence of ST elevation is characteristic of non-ST elevation myocardial infarction (NSTEMI) or unstable angina, collectively referred to as non-ST elevation acute coronary syndrome (NSTE-ACS). This typically results from partial coronary occlusion or transient complete occlusion, in contrast to STEMI, which shows ST elevation due to complete occlusion. -
USMLE Step 1 Medical Prep
Which of the following medications used in heart failure acts by inhibiting sodium-potassium ATPase?
Correct — B. Digoxin inhibits the sodium-potassium ATPase pump in cardiac myocytes, leading to increased intracellular sodium. This promotes increased calcium entry via the sodium-calcium exchanger, resulting in positive inotropy (increased contractility). Digoxin is used in heart failure to improve cardiac output and in atrial fibrillation to control ventricular rate. -
USMLE Step 1 Medical Prep
A 42-year-old woman presents with recurrent episodes of dizziness and syncope. ECG during an episode shows a prolonged QT interval of 520 ms. Which electrolyte abnormality is most likely to exacerbate this condition?
Correct — A. Hypokalemia prolongs the QT interval by delaying ventricular repolarization and is particularly dangerous in patients with congenital long QT syndrome. Low potassium levels can trigger torsades de pointes (a form of polymorphic ventricular tachycardia), which can lead to syncope or sudden cardiac death. -
USMLE Step 1 Medical Prep
In the cardiac cycle, which event corresponds to the onset of the first heart sound (S1)?
Correct — D. The first heart sound (S1) corresponds to the closure of the atrioventricular valves (mitral and tricuspid) at the beginning of ventricular systole. This occurs when ventricular pressure exceeds atrial pressure, causing the AV valves to snap shut, creating the 'lub' of 'lub-dub.' -
USMLE Step 1 Medical Prep
A 30-year-old woman has a blood pressure of 100/60 mmHg. What is her calculated mean arterial pressure (MAP)?
Correct — C. Mean arterial pressure (MAP) is calculated as: MAP = Diastolic pressure + (1/3 × Pulse pressure). Where pulse pressure = Systolic pressure - Diastolic pressure. MAP = 60 + (1/3 × (100-60)) = 60 + (1/3 × 40) = 60 + 13.3 ≈ 73 mmHg. -
USMLE Step 1 Medical Prep
Which of the following vessel layers is primarily responsible for maintaining vascular tone?
Correct — B. The tunica media (middle layer) of blood vessels contains smooth muscle cells and elastic fibers that control vessel diameter through contraction and relaxation. This layer is primarily responsible for maintaining vascular tone, which is crucial for regulating blood pressure and regional blood flow. -
USMLE Step 1 Medical Prep
A 68-year-old man with a history of myocardial infarction is started on lisinopril. Which of the following describes the primary mechanism of this medication?
Correct — A. Lisinopril is an angiotensin-converting enzyme (ACE) inhibitor that prevents the conversion of angiotensin I to angiotensin II. This leads to decreased aldosterone secretion, decreased vasoconstriction, and overall reduction in blood pressure. ACE inhibitors are beneficial in post-MI patients by reducing afterload and preventing adverse cardiac remodeling. -
USMLE Step 1 Medical Prep
A 57-year-old man with a 40-pack-year smoking history presents with leg pain when walking that resolves with rest. The pain is described as cramping in the calves. Which condition is most likely present?
Correct — D. This patient presents with classic symptoms of intermittent claudication, which is exercise-induced ischemic muscle pain that resolves with rest. It is typically caused by peripheral arterial disease (PAD), most commonly due to atherosclerosis. Smoking is a major risk factor for PAD, and the calf muscles are commonly affected due to their high oxygen demand during walking. -
USMLE Step 1 Medical Prep
Which of the following cells forms the majority of the cardiac conduction system?
Correct — C. Purkinje fibers form the majority of the specialized cardiac conduction system. They originate from the bundle of His and rapidly conduct electrical impulses throughout the ventricles, facilitating synchronized ventricular contraction. They have fewer myofibrils and more glycogen than regular cardiomyocytes, and conduct impulses about 4 times faster.
USMLE Step 1 Medical Prep sample questions
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USMLE Step 1 Medical Prep Which of the following medications used in heart failure acts by inhibiting sodium-potassium ATPase?
A. Furosemide
B. Digoxin ✓
C. Carvedilol
D. Lisinopril
Correct — B. Digoxin inhibits the sodium-potassium ATPase pump in cardiac myocytes, leading to increased intracellular sodium. This promotes increased calcium entry via the sodium-calcium exchanger, resulting in positive inotropy (increased contractility). Digoxin is used in heart failure to improve cardiac output and in atrial fibrillation to control ventricular rate.
USMLE Step 1 Medical Prep A 42-year-old woman presents with recurrent episodes of dizziness and syncope. ECG during an episode shows a prolonged QT interval of 520 ms. Which electrolyte abnormality is most likely to exacerbate this condition?
A. Hypokalemia ✓
B. Hyperkalemia
C. Hypercalcemia
D. Hypermagnesemia
Correct — A. Hypokalemia prolongs the QT interval by delaying ventricular repolarization and is particularly dangerous in patients with congenital long QT syndrome. Low potassium levels can trigger torsades de pointes (a form of polymorphic ventricular tachycardia), which can lead to syncope or sudden cardiac death.
USMLE Step 1 Medical Prep In the cardiac cycle, which event corresponds to the onset of the first heart sound (S1)?
A. Opening of the semilunar valves
B. Closure of the semilunar valves
C. Opening of the atrioventricular valves
D. Closure of the atrioventricular valves ✓
Correct — D. The first heart sound (S1) corresponds to the closure of the atrioventricular valves (mitral and tricuspid) at the beginning of ventricular systole. This occurs when ventricular pressure exceeds atrial pressure, causing the AV valves to snap shut, creating the 'lub' of 'lub-dub.'
USMLE Step 1 Medical Prep A 30-year-old woman has a blood pressure of 100/60 mmHg. What is her calculated mean arterial pressure (MAP)?
A. 60 mmHg
B. 67 mmHg
C. 73 mmHg ✓
D. 80 mmHg
Correct — C. Mean arterial pressure (MAP) is calculated as: MAP = Diastolic pressure + (1/3 × Pulse pressure). Where pulse pressure = Systolic pressure - Diastolic pressure. MAP = 60 + (1/3 × (100-60)) = 60 + (1/3 × 40) = 60 + 13.3 ≈ 73 mmHg.
USMLE Step 1 Medical Prep Which of the following vessel layers is primarily responsible for maintaining vascular tone?
A. Endothelium
B. Tunica media ✓
C. Tunica intima
D. Tunica adventitia
Correct — B. The tunica media (middle layer) of blood vessels contains smooth muscle cells and elastic fibers that control vessel diameter through contraction and relaxation. This layer is primarily responsible for maintaining vascular tone, which is crucial for regulating blood pressure and regional blood flow.
USMLE Step 1 Medical Prep A 68-year-old man with a history of myocardial infarction is started on lisinopril. Which of the following describes the primary mechanism of this medication?
A. Inhibition of angiotensin-converting enzyme ✓
B. Blockade of beta-adrenergic receptors
C. Antagonism of aldosterone receptors
D. Inhibition of phosphodiesterase
Correct — A. Lisinopril is an angiotensin-converting enzyme (ACE) inhibitor that prevents the conversion of angiotensin I to angiotensin II. This leads to decreased aldosterone secretion, decreased vasoconstriction, and overall reduction in blood pressure. ACE inhibitors are beneficial in post-MI patients by reducing afterload and preventing adverse cardiac remodeling.
USMLE Step 1 Medical Prep A 57-year-old man with a 40-pack-year smoking history presents with leg pain when walking that resolves with rest. The pain is described as cramping in the calves. Which condition is most likely present?
A. Deep vein thrombosis
B. Chronic venous insufficiency
C. Lumbar spinal stenosis
D. Peripheral arterial disease ✓
Correct — D. This patient presents with classic symptoms of intermittent claudication, which is exercise-induced ischemic muscle pain that resolves with rest. It is typically caused by peripheral arterial disease (PAD), most commonly due to atherosclerosis. Smoking is a major risk factor for PAD, and the calf muscles are commonly affected due to their high oxygen demand during walking.
USMLE Step 1 Medical Prep Which of the following cells forms the majority of the cardiac conduction system?
A. Epicardial cells
B. Myofibroblasts
C. Purkinje fibers ✓
D. Intercalated discs
Correct — C. Purkinje fibers form the majority of the specialized cardiac conduction system. They originate from the bundle of His and rapidly conduct electrical impulses throughout the ventricles, facilitating synchronized ventricular contraction. They have fewer myofibrils and more glycogen than regular cardiomyocytes, and conduct impulses about 4 times faster.
About the USMLE Step 1 Medical Prep test
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You will be tested on
- Safe and effective care environment
- Health promotion and maintenance
- Psychosocial and physiological integrity
- Pharmacology, infection control and patient safety
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Topics in this question bank
Safe and effective care environment
Health promotion and maintenance
Psychosocial and physiological integrity
Pharmacology, infection control and patient safety
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