USMLE Step 1 Renal Practice Questions

Which segment of the nephron is responsible for reabsorbing the largest fraction of the filtered load of water and solutes (Na+, K+, Cl-, HCO3-, glucose, amino acids)?

• (A) Proximal convoluted tubule (PCT)
• (B) Thick ascending limb of Loop of Henle
• (C) Distal convoluted tubule (DCT)
• (D) Collecting duct

What is the primary mechanism by which Angiotensin II increases blood pressure?

• (A) Vasoconstriction of arterioles and stimulation of aldosterone release
• (B) Vasodilation of arterioles and inhibition of ADH release
• (C) Increased glomerular filtration rate (GFR) only
• (D) Stimulation of renin release

Which hormone directly stimulates the insertion of aquaporin-2 (AQP2) channels into the apical membrane of principal cells in the collecting duct?

• (A) Antidiuretic hormone (ADH / Vasopressin)
• (B) Aldosterone
• (C) Atrial natriuretic peptide (ANP)
• (D) Parathyroid hormone (PTH)

What is the effect of Atrial Natriuretic Peptide (ANP) on the kidney?

• (A) Increases GFR and decreases Na+ reabsorption
• (B) Decreases GFR and increases Na+ reabsorption
• (C) Increases ADH release
• (D) Stimulates aldosterone secretion

In which segment of the nephron does parathyroid hormone (PTH) primarily stimulate calcium reabsorption?

• (A) Distal convoluted tubule (DCT)
• (B) Proximal convoluted tubule (PCT)
• (C) Thick ascending limb of Loop of Henle
• (D) Collecting duct

The calculation of Renal Plasma Flow (RPF) typically uses the clearance of which substance?

• (A) Para-aminohippuric acid (PAH)
• (B) Inulin
• (C) Creatinine
• (D) Glucose

What is the main function of the countercurrent multiplication mechanism involving the Loop of Henle?

• (A) Generation of a hypertonic medullary interstitium
• (B) Secretion of potassium
• (C) Reabsorption of glucose
• (D) Regulation of acid-base balance

Which diuretic class inhibits the Na+-Cl- cotransporter in the distal convoluted tubule?

• (A) Thiazide diuretics (e.g., hydrochlorothiazide)
• (B) Loop diuretics (e.g., furosemide)
• (C) Potassium-sparing diuretics (e.g., spironolactone)
• (D) Osmotic diuretics (e.g., mannitol)

Glomerular Filtration Rate (GFR) is defined as:

• (A) The volume of plasma filtered from the glomerular capillaries into Bowman's capsule per unit time
• (B) The volume of urine produced per unit time
• (C) The percentage of renal plasma flow that is filtered
• (D) The maximum rate of glucose reabsorption

What drives the filtration of plasma across the glomerular capillaries?

• (A) Net balance of hydrostatic and oncotic pressures (Starling forces)
• (B) Active transport of water
• (C) Action of ADH
• (D) Presence of fenestrated capillaries only

Which segment of the nephron is the principal site for secretion of potassium under normal and high potassium loads?

• (A) Collecting duct (principal cells)
• (B) Proximal convoluted tubule (PCT)
• (C) Thick ascending limb of Loop of Henle
• (D) Distal convoluted tubule (DCT)

How is glucose reabsorbed in the proximal convoluted tubule?

• (A) Secondary active transport coupled to Na+ (SGLT)
• (B) Primary active transport (ATPase)
• (C) Passive diffusion
• (D) Facilitated diffusion only

What is the effect of constriction of the afferent arteriole on GFR and RPF?

• (A) Decreases GFR and decreases RPF
• (B) Increases GFR and increases RPF
• (C) Increases GFR and decreases RPF
• (D) Decreases GFR and increases RPF

Which mechanism allows the kidney to maintain a relatively constant GFR despite fluctuations in systemic arterial blood pressure (autoregulation)?

• (A) Myogenic response and tubuloglomerular feedback (TGF)
• (B) Renin-angiotensin-aldosterone system (RAAS)
• (C) Sympathetic nervous system stimulation
• (D) Action of ADH

Fanconi syndrome is characterized by generalized dysfunction of which nephron segment, leading to impaired reabsorption of multiple solutes?

• (A) Proximal convoluted tubule (PCT)
• (B) Thick ascending limb
• (C) Distal convoluted tubule (DCT)
• (D) Collecting duct

What is the primary stimulus for renin release from juxtaglomerular (JG) cells?

• (A) Decreased renal perfusion pressure (detected by JG cells)
• (B) Increased NaCl delivery to the macula densa
• (C) Increased sympathetic stimulation (beta-1 receptors)
• (D) Increased plasma potassium concentration

Which substance's clearance represents the minimum possible urine osmolarity the kidney can produce?

• (A) Free water clearance (CH2O)
• (B) Osmolar clearance (Cosm)
• (C) Inulin clearance (GFR)
• (D) PAH clearance (RPF)

What is the function of the vasa recta in the kidney?

• (A) Maintain the medullary osmotic gradient (countercurrent exchange)
• (B) Filter blood to form ultrafiltrate
• (C) Secrete renin
• (D) Reabsorb glucose

Diabetes insipidus (either central or nephrogenic) results in the inability to:

• (A) Concentrate urine
• (B) Dilute urine
• (C) Reabsorb glucose
• (D) Secrete potassium

Which part of the nephron is responsible for secreting hydrogen ions (H+) and generating 'new' bicarbonate, particularly important in compensating for acidosis?

• (A) Collecting duct (alpha-intercalated cells)
• (B) Proximal convoluted tubule
• (C) Thick ascending limb
• (D) Macula densa

What is the filtration fraction (FF)?

• (A) The fraction of renal plasma flow (RPF) that is filtered across the glomerulus (FF = GFR / RPF)
• (B) The fraction of cardiac output going to the kidneys
• (C) The fraction of filtered water that is reabsorbed
• (D) The fraction of filtered Na+ that is excreted

Which diuretic works by blocking epithelial sodium channels (ENaC) in the principal cells of the collecting duct?

• (A) Amiloride or Triamterene (Potassium-sparing diuretics)
• (B) Spironolactone (Potassium-sparing diuretic)
• (C) Furosemide (Loop diuretic)
• (D) Hydrochlorothiazide (Thiazide diuretic)

What is the effect of severe sympathetic stimulation (e.g., during hemorrhage) on renal blood flow and GFR?

• (A) Decreases RBF and decreases GFR significantly
• (B) Increases RBF and increases GFR
• (C) Decreases RBF but maintains GFR via efferent constriction
• (D) No significant effect

Urea recycling contributes to which important renal process?

• (A) Maintaining the hypertonicity of the inner medullary interstitium
• (B) Reabsorbing glucose in the PCT
• (C) Secreting potassium in the collecting duct
• (D) Transporting PAH into the tubule

Acute Tubular Necrosis (ATN) most commonly affects which parts of the nephron due to their high metabolic activity and toxin exposure?

• (A) Proximal convoluted tubule and thick ascending limb
• (B) Glomerulus
• (C) Distal convoluted tubule
• (D) Collecting duct

Which force favors filtration across the glomerular capillaries?

• (A) Glomerular capillary hydrostatic pressure (P_GC)
• (B) Bowman's capsule hydrostatic pressure (P_BC)
• (C) Glomerular capillary oncotic pressure (π_GC)
• (D) Bowman's capsule oncotic pressure (π_BC)

What is the primary role of beta-intercalated cells in the collecting duct?

• (A) Secrete bicarbonate (HCO3-) and reabsorb H+
• (B) Secrete H+ and reabsorb HCO3-
• (C) Reabsorb Na+ and secrete K+
• (D) Reabsorb water

Which condition would lead to an increase in renin secretion?

• (A) Hemorrhage leading to hypotension
• (B) High dietary salt intake
• (C) Administration of an ACE inhibitor
• (D) Volume expansion

The macula densa cells are sensitive to the concentration of which substance in the tubular fluid of the distal tubule?

• (A) Sodium chloride (NaCl)
• (B) Glucose
• (C) Potassium (K+)
• (D) Urea

What is the effect of aldosterone on acid-base balance?

• (A) Promotes H+ secretion by alpha-intercalated cells
• (B) Promotes HCO3- secretion by beta-intercalated cells
• (C) Inhibits H+ secretion
• (D) Has no direct effect on H+ or HCO3- transport

Erythropoietin (EPO), a hormone essential for red blood cell production, is primarily synthesized by which cells in the kidney?

• (A) Interstitial fibroblasts in the cortex
• (B) Juxtaglomerular (JG) cells
• (C) Podocytes
• (D) Mesangial cells

A patient has a GFR of 120 mL/min and a plasma glucose concentration of 150 mg/dL (normal < 100 mg/dL, Tm for glucose ~375 mg/min). What is the approximate rate of glucose filtration?

• (A) 180 mg/min
• (B) 120 mg/min
• (C) 375 mg/min
• (D) 0 mg/min

In the context of the previous question (Filtered Load = 180 mg/min, Tm = 375 mg/min), what is the rate of glucose excretion?

• (A) 0 mg/min
• (B) 60 mg/min
• (C) 180 mg/min
• (D) 375 mg/min

Which ion's reabsorption in the thick ascending limb drives the reabsorption of other cations (like Ca2+ and Mg2+) via the paracellular pathway?

• (A) Sodium (Na+) and Chloride (Cl-) reabsorption creating a lumen-positive potential
• (B) Potassium (K+) secretion
• (C) Bicarbonate (HCO3-) reabsorption
• (D) Phosphate reabsorption

Where in the nephron does ADH exert its primary effect on urea permeability?

• (A) Medullary collecting duct
• (B) Proximal convoluted tubule
• (C) Thin descending limb of Loop of Henle
• (D) Distal convoluted tubule

Which force opposes glomerular filtration?

• (A) Glomerular capillary oncotic pressure (π_GC) and Bowman's capsule hydrostatic pressure (P_BC)
• (B) Glomerular capillary hydrostatic pressure (P_GC) only
• (C) Systemic arterial pressure
• (D) Renal plasma flow

What metabolic abnormality is commonly associated with the use of loop diuretics like furosemide?

• (A) Hypokalemia and metabolic alkalosis
• (B) Hyperkalemia and metabolic acidosis
• (C) Hypocalcemia
• (D) Hypernatremia

The ability of the kidney to produce concentrated urine depends critically on:

• (A) Hypertonic medullary interstitium and ADH action on the collecting duct
• (B) High glomerular filtration rate
• (C) Secretion of urea in the PCT
• (D) Absence of aldosterone

What percentage of the filtered water is typically reabsorbed by the end of the proximal convoluted tubule?

• (A) 65-70%
• (B) 10-20%
• (C) 99%
• (D) 50%

Which enzyme, located in juxtaglomerular cells, catalyzes the conversion of angiotensinogen to angiotensin I?

• (A) Renin
• (B) Angiotensin-converting enzyme (ACE)
• (C) Carbonic anhydrase
• (D) Na+/K+-ATPase