USMLE Step 1 study guide
USMLE Step 1 · Work through your exam, one topic at a time.
Step 1 is the first of the three examinations in the United States Medical Licensing Examination (USMLE) program, which is jointly owned by the Federation of State Medical Boards (FSMB) and the National Board of Medical Examiners (NBME). It assesses whether an examinee understands and can apply important concepts of the sciences basic to the practice of medicine, with special emphasis on principles and mechanisms underlying health, disease, and modes of therapy. The USMLE Step 1 study guide has 10 sections and about 3,442 words.
01General Principles of Foundational Science
Enzyme kinetics: Km is the substrate concentration at half-maximal velocity and varies inversely with affinity; Vmax reflects enzyme amount. Competitive inhibitors raise Km with unchanged Vmax; noncompetitive inhibitors lower Vmax; mixed inhibitors alter both.
288 words, about 1 min02Behavioral Health & Nervous Systems/Special Senses
Learn the classic stroke syndromes. Lateral medullary (PICA): ipsilateral Horner syndrome, ataxia, facial pain/temperature loss, dysphagia, hoarseness, plus contralateral body pain/temperature loss.
316 words, about 2 min03Blood & Lymphoreticular/Immune Systems
Microcytic: iron deficiency (low ferritin, high TIBC, high RDW), thalassemia (normal or high ferritin, target cells, family history), anemia of chronic disease (low TIBC, high ferritin), lead poisoning (basophilic stippling). Macrocytic: B12 versus folate deficiency, distinguishing neurologic findings and methylmalonic acid.
318 words, about 2 min04Cardiovascular System
Map the cardiac cycle: S1 is atrioventricular valve closure, S2 semilunar closure; S3 reflects volume overload or early filling, S4 a stiff ventricle with an atrial kick. On the pressure-volume loop, end-diastolic volume tracks preload, end-systolic volume tracks afterload and contractility.
304 words, about 2 min05Endocrine System
Every endocrine axis follows the same pattern: hypothalamic releasing hormone, pituitary trophic hormone, target gland hormone with negative feedback. In primary target-gland failure the trophic hormone is elevated and the target hormone low; in secondary failure both are low.
292 words, about 1 min06Gastrointestinal System
Gastrin from antral G cells drives acid secretion; CCK from duodenal I cells drives gallbladder contraction and pancreatic enzyme secretion and relaxes the sphincter of Oddi; secretin from S cells drives pancreatic bicarbonate. Parietal cells secrete acid and intrinsic factor; chief cells secrete pepsinogen.
330 words, about 2 min07Musculoskeletal System, Skin & Subcutaneous Tissue
Osteoblasts form bone, express alkaline phosphatase, and secrete RANK ligand; osteoclasts resorb bone under RANK stimulation and are TRAP positive. PTH drives bone resorption indirectly, vitamin D increases gut calcium absorption, calcitonin inhibits osteoclasts, and estrogen restrains osteoclast activity.
644 words, about 3 min08Renal & Urinary System
The proximal tubule reabsorbs about 65 percent of filtered sodium and water isotonically, with brush-border and carbonic anhydrase activity. The thin descending limb is water permeable; the thick ascending limb uses the sodium-potassium-2-chloride cotransporter, is water impermeable, and dilutes urine (loop diuretic site).
294 words, about 1 min09Reproductive System
GnRH pulses drive LH and FSH. In the ovary, LH stimulates theca cells to make androgens and FSH stimulates granulosa cells to aromatize them into estradiol.
323 words, about 2 min10Respiratory System
Compliance is the change in volume per change in pressure; elastance is its reciprocal. Surfactant from type II pneumocytes lowers surface tension and prevents alveolar collapse per the law of Laplace, so premature infants develop respiratory distress with atelectasis.
333 words, about 2 min