USMLE Step 1 Physiology Questions
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Free USMLE Step 1 Physiology Questions

A 22-year-old male college student volunteers for a research study relating to renal functions. He undergoes several laboratory tests:





0 mg/dl

93 mg/dl


100 mg/dl

1.0 mg/dl

Para-Aminohippurate (PAH)

150 mg/dl

0.2 mg/dl




Urine Flow Rate



What is his estimated renal blood flow?

  1. 200 mL/min
  2. 1,000 mL/min
  3. 1,500 mL/min
  4. 750 ml/min
  5. 3,000 mL/min

A 27-year-old female visits her doctor with the complaint of pain in her anterior neck that radiates to her ears for the past three weeks. She also mentions that she has been experiencing palpitations, muscle weakness, increased sweating and an increase in the frequency of defecation. Two months ago she says that she had a bad flu. She has had no such symptoms in the past. She neither consumes alcohol nor smokes cigarettes. On examination, the physician notices the patient to be garrulous and restless. There is presence of fine tremors in both hands. His pulse is 104/min and irregular, blood pressure is 140/80 mm Hg. The anterior neck is swollen, warm to touch and markedly tender on palpation. Thyroid function tests and a biopsy are ordered. The result of the biopsy is depicted in the picture below. Which of the following deviations from the normal is expected to be seen in her thyroid function tests?

  1. Normal Serum TSH, ↑ Total T4, Normal Free T4, Normal I131 Uptake
  2. ↓ Serum TSH, ↑ Total T4, ↑ Free T4, ↑ I131 Uptake
  3. ↓ Serum TSH, ↑ Total T4, ↑ Free T4, ↓ I131 Uptake
  4. Normal Serum TSH, ↓ Total T4, Normal Free T4, Normal I131 Uptake
  5. ↑ Serum TSH, ↑ Total T4, ↑ Free T4, ↑ I 131 Uptake
Physiology USMLE Step 1 Practice Question

Image by Nephron, License: CC BY-SA 3.0

A healthy 22-year-old male participates in a research study you are leading to compare the properties of skeletal and cardiac muscle. You conduct a three-phased experiment with the participant. In the first phase, you get him to lift up a 5 lbs weight off a table with his left hand. In the second phase, you get him to do 20 burpees, taking his heart rate to 150 bpm. In the third phase, you electrically stimulate his gastrocnemius with a frequency of 50 Hz. You are interested in the tension and electrical activity of specific muscles as follows: Biceps in phase 1, cardiac muscle in phase 2 and gastrocnemius in phase 3. What would you expect to be happening in the phases and the respective muscles of interest?

  1. Recruitment of small motor units at the start of experiments 1 and 2
  2. Increase of tension in experiments 2 and 3, with the same underlying mechanism
  3. Recruitment of large motor units followed by small motor units in experiment 1
  4. Fused tetanic contraction at the end of all three experiments
  5. Increase of tension in all phases

A 20-year-old healthy female volunteer is enrolled in a study on renal perfusion. Her medical history is unremarkable and she takes no medications. She denies smoking, drinking and drug use. Her family history is unremarkable. Examination reveals no abnormal findings. A drug which is known to very selectively act on a segment of the renal vasculature is administered and her glomerular filtration rate (GFR) and filtration fraction (FF) both increase. Which of the following could be the mechanism of action of the administered drug?

  1. Efferent arteriole constriction
  2. Renal artery constriction
  3. Efferent arteriole dilation
  4. Increased peritubular capillary permeability
  5. Afferent arteriole constriction

Mutations in the ATP2A1 gene results in loss of function of the calcium ATPase pump found in the membranes of sarcoplasmic reticulum in skeletal muscle in humans. This results in a rare disease characterized by muscle cramping and stiffening usually most severe after exercise or strenuous activity that is typically relieved after affected individuals rest for a few minutes. Which of the following is expected to be seen in such individuals?

  1. Muscle relaxation time: decreased, cytosolic calcium concentration: increased
  2. Muscle relaxation time: increased, cytosolic calcium concentration: increased
  3. Muscle relaxation time: increased, cytosolic calcium concentration: no change
  4. Muscle relaxation time: no change, cytosolic calcium concentration: decreased
  5. Muscle relaxation time: increased, cytosolic calcium concentration: decreased

35-year-old female volunteers for a study on respiratory physiology. Two pressure probes are placed as follows:

  • Probe A: between the parietal and visceral pleura
  • Probe B: within the cavity of an alveoli

The probes provide a pressure reading relative to atmospheric pressure. To obtain a baseline reading, she is asked to sit comfortably and breathe normally. Which of the following set of values will most likely be seen at the end of inspiration?

  1. Probe A: 0 mm HgrnrnProbe B: 0 mm Hg
  2. Probe A: 0 mm HgrnrnProbe B: -1 mm Hg
  3. Probe A: -4 mm HgrnrnProbe B: 0 mm Hg
  4. Probe A: -4 mm HgrnrnProbe B: -1 mm Hg
  5. Probe A: -6 mm HgrnrnProbe B: 0 mm Hg
  6. Probe A: -6 mm HgrnrnProbe B: -1 mm Hg

A 23-year-old man presents to the physician with nausea, vomiting, constipation, and abdominal pain for one day. Since that morning, he has also developed difficulty in swallowing and blurring of vision. He also complains of significant dryness of mouth and throat. When asked about his diet, he reports that he has been saving money by eating dented and old canned goods. On physical examination, his vital signs are stable. His neurologic examination reveals bilateral fixed dilated pupils, weakness of extraocular muscles, and weak gag reflex while sensations and gait are normal. Laboratory evaluation of his stool isolates a toxin produced by gram-positive, anaerobic, spore-forming bacilli. Which of the following mechanisms best explains the action of the toxin?

  1. Blockade of voltage-gated fast sodium channels in motor neurons
  2. Blockade of release of acetylcholine at neuromuscular junctions
  3. Inactivation of acetylcholinesterase at neuromuscular junctions
  4. Competitive antagonism of acetylcholine at postsynaptic receptors
  5. Prolonged depolarization of NM receptors

A 32-year-old woman comes to the doctor’s office for a regular health checkup. She does not have any complaints at this visit and mentions that she has started to train for an upcoming marathon and drinks a lot of electrolyte solution these days to keep herself hydrated. She has been trying to quit smoking for a few years now but has been unable to. She has hypercholesterolemia which is controlled by a low-calorie diet. Family history is significant for hypertension in both of her parents. Her father died of heart attack a few years ago. Her vitals are heart rate: 55/min, respiratory rate: 16/min, temperature: 37.6 °C (99.68 °F) and blood pressure: 120/88 mm Hg. Physical exam findings are within normal limits. A routine ECG is done and is shown below.  The abnormal wave seen on her ECG tracing represents which of the following mechanical events?

  1. Ventricular depolarization
  2. Period between ventricular depolarization and repolarization
  3. Ventricular repolarization
  4. Atrial depolarization
  5. Atrial repolarization
Physiology USMLE Step 1 Practice Question

Image: by James Heilman,, License: CC BY-SA 4.0

A 5-year-old girl swallows a marble while playing and is rushed to the hospital by her mother. Her mother is very concerned after she started to cough violently and made 'funny breathing' sounds for a few minutes. Her pulse is 100/min and respirations are 28/min. Physical examination reveals a girl in no obvious distress and breathing comfortably. Auscultation reveals diminished breath sounds over the lower right lung field and a mild expiratory wheeze in the same area. The examination is otherwise unremarkable. A chest X-ray shows a round foreign body about 1x1 cm in the lower portion of the right inferior lobe. Which of the following changes is expected in the blood flow through the affected part of the lung?

  1. Increased due to arterial vasodilation
  2. Increased due to active hyperemia
  3. Unchanged due to autoregulation
  4. Unchanged due to decreased surfactant
  5. Decreased due to arterial vasoconstriction
  6. Decreased due to local inflammation

A healthy 22-year-old male volunteers for a study on lung function. He has no history of lung disease or allergies and does not smoke. His pulmonary blood flow is measured in the various labeled segments of the lungs while standing. Then the volunteer, still standing, is given very low continuous airway pressure and the blood flow measured again. Which set of findings below are expected in the second measurements as compared to the first?

  1. Reduced blood flow in zone 1
  2. Increased blood flow in zone 1
  3. Increased blood flow in zone 2
  4. Reduced blood flow in zone 3
  5. Increased blood flow in zone 3
Physiology USMLE Step 1 Practice Question

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