USMLE Step 1 Quiz
Practice Renal Physiology And Filtration in USMLE Step 1 with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.
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A 58-year-old man with diabetes and hypertension has eGFR 28 mL/min/1.73 m² and potassium 5.8 mEq/L. ECG shows peaked T waves. Which of the following interventions is most appropriate given the renal function test results?
This quiz focuses on Renal Physiology And Filtration, giving you a quick way to practice the rules, question types, and explanations that matter most for USMLE Step 1.
Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.
A 58-year-old man with diabetes and hypertension has eGFR 28 mL/min/1.73 m² and potassium 5.8 mEq/L. ECG shows peaked T waves. Which of the following interventions is most appropriate given the renal function test results?
Explanation: This question tests understanding of renal physiology and filtration mechanisms (USMLE Step 1). Renal filtration involves the glomerulus where blood pressure and oncotic pressure affect GFR. In this scenario, the patient's lab results and clinical presentation indicate hyperkalemia in CKD with cardiac effects. The correct answer (Choice A) is supported by stabilizing membranes and shifting potassium, appropriate for low eGFR and ECG changes. Choice B is incorrect because it assumes hyperkalemia is solely from dehydration, a common error when students overlook CKD's impaired potassium excretion. Teaching strategies include emphasizing the role of pressure dynamics in GFR regulation and practicing with clinical scenarios to apply physiological principles. Reinforce understanding of renal pathophysiology through case-based learning.
A 62-year-old woman with diabetes has persistent albuminuria and eGFR 42 mL/min/1.73 m². BP 156/94 mmHg. Which of the following interventions is most appropriate given the renal function test results?
Explanation: This question tests understanding of renal physiology and filtration mechanisms (USMLE Step 1). Renal filtration involves the glomerulus where blood pressure and oncotic pressure affect GFR. In this scenario, the patient's lab results and clinical presentation indicate diabetic CKD with proteinuria and hypertension. The correct answer (Choice A) is supported by reducing efferent tone to lower glomerular pressure, explaining the benefit in slowing CKD progression. Choice B is incorrect because it assumes NSAIDs improve GFR long-term, a common error when students overlook their risk in CKD. Teaching strategies include emphasizing the role of pressure dynamics in GFR regulation and practicing with clinical scenarios to apply physiological principles. Reinforce understanding of renal pathophysiology through case-based learning.
A 64-year-old woman with heart failure is treated aggressively with loop diuretics and has dizziness and oliguria. BP 88/54 mmHg. BUN 54 mg/dL, creatinine 2.0 mg/dL. FeNa 0.3%. What is the next step in managing this patient's renal dysfunction?
Explanation: This question tests understanding of renal physiology and filtration mechanisms (USMLE Step 1). Renal filtration involves the glomerulus where blood pressure and oncotic pressure affect GFR. In this scenario, the patient's lab results and clinical presentation indicate prerenal azotemia from overdiuresis in heart failure. The correct answer (Choice A) is supported by restoring volume to improve perfusion and GFR, explaining the patient's oliguria and low FeNa. Choice B is incorrect because it assumes converting to intrinsic failure with more diuretics, a common error when students overlook volume restoration in prerenal states. Teaching strategies include emphasizing the role of pressure dynamics in GFR regulation and practicing with clinical scenarios to apply physiological principles. Reinforce understanding of renal pathophysiology through case-based learning.
A 68-year-old man presents with 1 day of oliguria after vomiting and diarrhea. BP 92/56 mmHg, dry mucous membranes. BUN 68 mg/dL, creatinine 2.4 mg/dL, FeNa 0.4%, UA bland. Which mechanism best explains the patient's decreased GFR?
Explanation: This question tests understanding of renal physiology and filtration mechanisms (USMLE Step 1). Renal filtration involves the glomerulus where blood pressure and oncotic pressure affect GFR. In this scenario, the patient's lab results and clinical presentation indicate prerenal azotemia due to hypovolemia. The correct answer (Choice B) is supported by the principle of reduced renal perfusion decreasing glomerular hydrostatic pressure, explaining the patient's oliguria and elevated creatinine. Choice A is incorrect because it assumes prostaglandin excess causes afferent dilation, a common error when students overlook the role of decreased perfusion in prerenal states. Teaching strategies include emphasizing the role of pressure dynamics in GFR regulation and practicing with clinical scenarios to apply physiological principles. Reinforce understanding of renal pathophysiology through case-based learning.
A 57-year-old man has longstanding hypertension and now has progressive CKD. Which intervention is most appropriate to slow further decline in GFR?
Explanation: This question tests understanding of renal physiology and filtration mechanisms (USMLE Step 1). Renal filtration involves the glomerulus where blood pressure and oncotic pressure affect GFR. In this scenario, the patient's lab results and clinical presentation indicate hypertensive CKD progression. The correct answer (Choice A) is supported by controlling glomerular hypertension to preserve nephrons, explaining the benefit in slowing GFR decline. Choice B is incorrect because it assumes NSAIDs preserve GFR, a common error when students overlook their risks in CKD. Teaching strategies include emphasizing the role of pressure dynamics in GFR regulation and practicing with clinical scenarios to apply physiological principles. Reinforce understanding of renal pathophysiology through case-based learning.
A 9-year-old boy is brought to the pediatrician due to periorbital edema and swelling of his feet. Urinalysis reveals 4+ proteinuria. A diagnosis of minimal change disease is made. The significant loss of albumin in the urine leads to hypoalbuminemia, which alters the Starling forces governing glomerular filtration.
Which of the following changes in Starling forces across the glomerular capillary is the primary driver of the increased glomerular filtration rate sometimes seen in early nephrotic syndrome?
Explanation: In nephrotic syndrome, massive proteinuria leads to hypoalbuminemia, which decreases the plasma oncotic pressure within the glomerular capillaries. Glomerular filtration is determined by the balance of hydrostatic and oncotic pressures. A decrease in the glomerular capillary oncotic pressure, which normally opposes filtration, leads to an increased net filtration pressure and thus a higher GFR. Bowman's space oncotic pressure is normally negligible and would increase, not decrease, with proteinuria, opposing filtration.
A 5-year-old girl is diagnosed with an inherited disorder characterized by generalized dysfunction of the proximal convoluted tubule. Laboratory studies show glucosuria, aminoaciduria, and phosphaturia despite normal plasma concentrations of these substances.
This patient's condition is primarily caused by a defect in which of the following renal physiologic processes?
Explanation: The patient's presentation is consistent with Fanconi syndrome, a disorder of generalized proximal convoluted tubule (PCT) dysfunction. The PCT is responsible for reabsorbing the majority of filtered glucose, amino acids, phosphate, bicarbonate, and low-molecular-weight proteins. These substances are primarily reabsorbed via sodium-coupled cotransport mechanisms. A defect in these transporters leads to the wasting of these solutes in the urine.
A 24-year-old woman sustains a head injury in a car accident and subsequently develops polyuria and hypernatremia. A water deprivation test confirms a diagnosis of central diabetes insipidus. In this condition, the kidneys are unable to concentrate urine due to a lack of ADH.
In the absence of ADH, tubular fluid is most dilute in which segment of this patient's nephron?
Explanation: The thick ascending limb of the loop of Henle actively reabsorbs NaCl without water, making the tubular fluid hypotonic (dilute). This process continues in the distal convoluted tubule (DCT), which is also impermeable to water in the absence of ADH. Therefore, the fluid becomes even more dilute as it passes through the DCT. In the absence of ADH, the collecting duct remains impermeable to water, and this dilute fluid is excreted as urine. The fluid is most dilute at the end of the diluting segments, which culminates in the DCT and collecting ducts.
A 45-year-old woman is participating in a clinical trial to assess her kidney function. She is given a continuous infusion of para-aminohippuric acid (PAH) until a steady-state plasma concentration is reached. Urine and plasma samples are collected to calculate its clearance.
The clearance of PAH is used clinically to provide an estimate of which of the following renal parameters?
Explanation: Para-aminohippuric acid (PAH) is an organic acid that is both freely filtered by the glomerulus and avidly secreted by the proximal tubule. At low plasma concentrations, virtually all PAH that enters the kidney is removed from the plasma and excreted in the urine. Therefore, its clearance rate is approximately equal to the total renal plasma flow (RPF). Inulin or creatinine clearance is used to estimate GFR.
An 80-year-old man with severe osteoarthritis has been taking high doses of ibuprofen, a nonsteroidal anti-inflammatory drug (NSAID), for chronic knee pain. He presents to his physician with fatigue and is found to have an acute increase in his serum creatinine.
The renal dysfunction in this patient is most likely caused by the inhibition of prostaglandin synthesis, which leads to which of the following changes in renal vasculature?
Explanation: Prostaglandins (particularly PGE2 and PGI2) are local vasodilators that are important for maintaining renal blood flow, especially in states of reduced effective circulating volume (e.g., dehydration, heart failure, elderly). They preferentially dilate the afferent arteriole. NSAIDs like ibuprofen inhibit cyclooxygenase (COX) enzymes, blocking prostaglandin synthesis. This leads to unopposed constriction of the afferent arteriole, reducing renal blood flow and GFR, which can precipitate acute kidney injury.
A 22-year-old woman with type 1 diabetes mellitus presents with a 2-day history of polyuria and polydipsia. Her blood glucose is 450 mg/dL. A urinalysis is positive for glucose.
The presence of glucose in this patient's urine is best explained by which of the following mechanisms?
Explanation: Glucose is freely filtered at the glomerulus and is almost completely reabsorbed in the proximal convoluted tubule by sodium-glucose cotransporters (SGLT). These transporters have a finite capacity, known as the transport maximum (Tm). When the filtered load of glucose (GFR x plasma glucose concentration) exceeds the Tm (typically when plasma glucose is >200 mg/dL), the transporters become saturated, and the excess glucose is excreted in the urine, resulting in glucosuria.
A 48-year-old woman is diagnosed with an aldosterone-secreting adrenal adenoma (Conn's syndrome). She presents with hypertension, hypokalemia, and metabolic alkalosis.
The physiologic effects of excess aldosterone in this patient are mediated primarily through increased activity of which transporters in the principal cells of the collecting duct?
Explanation: Aldosterone is a mineralocorticoid that acts on the principal cells of the late distal tubule and collecting duct. It increases the expression and activity of the apical epithelial sodium channel (ENaC), leading to increased Na+ reabsorption. It also upregulates the basolateral Na+/K+-ATPase pump, which provides the driving force for Na+ reabsorption and K+ secretion. The resulting Na+ retention causes hypertension, and the enhanced K+ secretion leads to hypokalemia.
A 59-year-old woman is found to have a serum calcium level of 12.1 mg/dL. Further workup reveals a parathyroid adenoma causing primary hyperparathyroidism. Parathyroid hormone (PTH) has significant effects on renal tubular transport.
Which of the following sets of effects on renal tubular transport is most consistent with the action of PTH?
Explanation: Parathyroid hormone (PTH) acts to increase serum calcium and decrease serum phosphate. In the kidney, PTH has two major effects: 1) It inhibits the Na+/phosphate cotransporter in the apical membrane of the proximal tubule, leading to decreased phosphate reabsorption (phosphaturia). 2) It stimulates calcium reabsorption in the distal convoluted tubule by increasing the expression of the apical Ca2+ channel (TRPV5).
A 45-year-old man with a traumatic brain injury is being treated with an intravenous infusion of mannitol to reduce intracranial pressure. Shortly after the infusion begins, the nursing staff notes a significant increase in his urine output.
The diuretic effect of mannitol is primarily due to which of the following mechanisms?
Explanation: Mannitol is an osmotic diuretic. It is a sugar that is freely filtered at the glomerulus but is not reabsorbed by the renal tubules. As it remains in the tubular lumen, it increases the osmolarity of the tubular fluid. This osmotic force opposes the reabsorption of water, particularly in the proximal tubule and descending limb of the loop of Henle, leading to an increased volume of water remaining in the tubule and a subsequent increase in urine output.
A 25-year-old soldier is on a training exercise in the desert with limited access to water. After 12 hours, he is significantly dehydrated. His posterior pituitary is releasing maximal amounts of ADH in response to hyperosmolality.
Which of the following best describes the expected state of this soldier's free-water clearance (CH2O)?
Explanation: Free-water clearance (CH2O) is the rate at which solute-free water is excreted by the kidneys. It is calculated as V - Uosm/Posm * V, where V is urine flow rate. In a state of dehydration, high levels of ADH cause maximal water reabsorption in the collecting ducts, leading to the production of a small volume of highly concentrated urine (Uosm >> Posm). This results in a negative free-water clearance, indicating that the kidneys are conserving water and returning solute-free water to the body.
A 44-year-old man with severe chronic obstructive pulmonary disease (COPD) develops chronic respiratory acidosis with a PCO2 of 65 mm Hg. The kidneys begin to compensate for this acid-base disturbance over several days.
Which of the following represents the primary renal compensatory mechanism for chronic respiratory acidosis?
Explanation: In chronic respiratory acidosis, the kidneys compensate by increasing net acid excretion to generate new bicarbonate. This occurs through: 1) Enhanced H+ secretion by α-intercalated cells in the collecting duct, 2) Increased ammonia production from glutamine in the proximal tubule cells, which allows for greater buffering of secreted H+ and net acid excretion, and 3) Increased reabsorption of filtered bicarbonate. The generation of new bicarbonate through net acid excretion (particularly via the ammonia system) is the key mechanism that raises plasma bicarbonate levels to compensate for the respiratory acidosis.
A 67-year-old man with a history of atherosclerosis presents with new-onset, difficult-to-control hypertension. An abdominal bruit is heard on examination. Angiography confirms a high-grade stenosis of the right renal artery. This condition leads to a marked increase in renin and angiotensin II levels.
How does the elevated angiotensin II level in this patient help preserve the glomerular filtration rate in the affected kidney?
Explanation: Renal artery stenosis reduces perfusion pressure to the glomerulus, which would otherwise decrease GFR. The resulting activation of the renin-angiotensin-aldosterone system produces high levels of angiotensin II. Angiotensin II is a potent vasoconstrictor that has a greater effect on the efferent arteriole than the afferent arteriole. This preferential efferent constriction increases the resistance to blood outflow from the glomerulus, thereby raising the glomerular hydrostatic pressure and helping to maintain GFR despite the reduced renal blood flow.
A 68-year-old man with decompensated heart failure is administered intravenous furosemide. Within an hour, he experiences a significant increase in urine output. Furosemide is a potent diuretic that acts on a specific segment of the nephron to inhibit salt reabsorption.
This drug exerts its primary effect by inhibiting which of the following transport processes in the thick ascending limb of the loop of Henle?
Explanation: Furosemide is a loop diuretic that acts on the thick ascending limb (TAL) of the loop of Henle. Its mechanism of action is the inhibition of the Na+/K+/2Cl- cotransporter (NKCC2) on the apical membrane of TAL cells. By blocking this transporter, furosemide prevents the reabsorption of these ions, which disrupts the generation of the corticomedullary osmotic gradient and leads to a powerful natriuretic and diuretic effect.
A research study is conducted to evaluate the renal handling of a new drug, substance Y. The clearance of inulin, a substance that is freely filtered but not reabsorbed or secreted, is measured to be 120 mL/min. The clearance of substance Y is calculated to be 80 mL/min.
Based on these findings, which of the following best describes the net handling of substance Y by the renal tubules?
Explanation: The clearance of inulin is used to measure the glomerular filtration rate (GFR). In this case, GFR is 120 mL/min. The clearance of a substance represents the volume of plasma from which the substance is completely removed per unit time. If the clearance of substance Y (80 mL/min) is less than the GFR (120 mL/min), it means that less substance is being excreted in the urine than was filtered at the glomerulus. This indicates that there is net tubular reabsorption of substance Y.
A healthy volunteer consumes a large volume of isotonic saline. This volume expansion leads to an increased glomerular filtration rate and subsequently, an increased delivery of NaCl to the distal nephron.
The increased delivery of NaCl to the macula densa cells will trigger which of the following immediate responses as part of the tubuloglomerular feedback mechanism?
Explanation: The tubuloglomerular feedback (TGF) mechanism is a key component of renal autoregulation. The macula densa cells in the distal tubule sense the NaCl concentration in the tubular fluid. An increased delivery of NaCl, as would occur with an increased GFR, causes the macula densa to release adenosine and ATP. These paracrine factors act on the adjacent afferent arteriole, causing it to constrict. This constriction reduces glomerular blood flow and hydrostatic pressure, thereby returning the GFR back toward normal.