Friday's Big Fat Kidney Quiz

 

This 35 question renal quiz is designed for medical students and covers key concepts in kidney structure, function, and pathophysiology. As always, you can answer anonymously, with immediate feedback, and can try again as often as you like.

A patient with long-standing autoimmune disease develops fatigue and haematuria. Blood tests show elevated creatinine and low complement levels. Which renal condition is most likely?

A. IgA nephropathy
B. Diabetic nephropathy
C. Lupus nephritis
D. Acute pyelonephritis
E. Minimal change disease

✅ Correct answer: C. Lupus nephritis. Lupus nephritis is a manifestation of systemic lupus erythematosus. It involves immune complex deposition in the glomeruli and often presents with low complement levels and renal impairment.

Which of the following features best distinguishes the descending limb of the loop of Henle?

A. Actively reabsorbs sodium
B. Is impermeable to water
C. Passively reabsorbs water
D. Actively secretes hydrogen ions
E. Reabsorbs glucose

✅ Correct answer: C. Passively reabsorbs water. The descending limb is permeable to water but not to solutes. As the filtrate moves down into the hypertonic medulla, water is passively drawn out, concentrating the filtrate.

A 22-year-old woman presents with dysuria and frequency. Midstream urine shows pyuria and bacteriuria and E.Coli is the suspected pathogen. What structural feature of uropathogenic E. coli helps it adhere to uroepithelium and cause infection?

A. Lipopolysaccharide
B. Flagella
C. P fimbriae
D. Beta-lactamase
E. Biofilm formation

✅ Correct answer: C. P fimbriae. P fimbriae are adhesins that enable E. coli to bind tightly to uroepithelial cells, resisting flushing by urine. This contributes to its pathogenicity in UTIs, especially pyelonephritis.

A 70-year-old man presents with reduced urine output and rising creatinine over 2 days. He has no previous creatinine result on record. Which of the following findings would suggest chronic kidney disease rather than acute kidney injury?

A. Elevated serum potassium
B. Oliguria
C. Normocytic anaemia
D. Nausea and vomiting
E. Elevated urea

✅ Correct answer: C. Normocytic anaemia. Normocytic anaemia is typical of chronic kidney disease due to reduced erythropoietin production over time and helps distinguish it from acute kidney injury, where red cell production is usually unaffected. Elevated potassium (A) and urea (E) can be seen in both acute and chronic kidney dysfunction and are not useful in differentiating the two. Oliguria (B) is more characteristic of acute kidney injury, especially with sudden drops in perfusion or obstruction, while patients with chronic kidney disease often maintain normal urine output. Nausea and vomiting (D) are nonspecific uraemic symptoms and can occur in both acute and chronic settings.

A 16-year-old presents with dysuria and suprapubic pain. Urine microscopy shows pyuria and bacteriuria. What is the most likely pathophysiological mechanism?

A. Glomerular immune complex deposition
B. Ascending infection from urethra
C. Reduced GFR due to dehydration
D. Crystal precipitation in tubules
E. Tubular ischaemia

✅ Correct answer: B. Ascending infection from urethra. Most urinary tract infections (especially cystitis) result from bacteria ascending from the urethra into the bladder. This is common in females due to a shorter urethra.

A 35-year-old has normal GFR but persistent metabolic acidosis with a normal anion gap. Which mechanism most likely explains this?

A. Impaired ammonium excretion
B. Excessive bicarbonate filtration
C. High aldosterone levels
D. Increased water reabsorption
E. Increased glomerular permeability

✅ Correct answer: A. Impaired ammonium excretion. In renal tubular acidosis, the kidneys cannot excrete acid (as ammonium), leading to a non-anion gap metabolic acidosis. GFR can remain normal.

A 52-year-old man with known heart failure and low blood pressure has a sudden drop in urine output. BP is 90/60 mmHg, and creatinine has doubled from baseline. Which of the following best describes this type of renal injury?

A. Intrinsic renal failure
B. Post-renal obstruction
C. Pre-renal acute kidney injury
D. Chronic kidney disease
E. Acute glomerulonephritis

✅ Correct answer: C. Pre-renal acute kidney injury. Low perfusion from hypotension reduces blood flow to the kidneys, causing pre-renal AKI. The kidneys themselves are structurally intact, and reversing the perfusion deficit often restores function.

Which of the following substances is normally not present in significant amounts in healthy urine?

A. Urea
B. Sodium
C. Potassium
D. Glucose
E. Creatinine

✅ Correct answer: D. Glucose. In healthy kidneys, glucose is filtered by the glomerulus and almost completely reabsorbed in the proximal tubule. Glucosuria usually indicates hyperglycaemia exceeding the renal threshold.

Why is serum urea a less reliable marker of kidney function than creatinine?

A. Urea is not filtered by the glomerulus
B. Urea is secreted into the tubules
C. Urea levels are unaffected by hydration
D. Urea is reabsorbed in the tubules
E. Urea is produced at a constant rate

✅ Correct answer: D. Urea is reabsorbed in the tubules. Unlike creatinine, which is mostly filtered and not reabsorbed, urea is partly reabsorbed in the tubules. This makes it more sensitive to hydration status and less specific for GFR.

A 60-year-old with long-standing hypertension presents with fatigue and poor appetite. Bloods show eGFR of 28 mL/min/1.73m² (reduced) and normocytic anaemia. What best explains his anaemia?

A. Vitamin B12 deficiency
B. Bone marrow infiltration
C. Reduced erythropoietin production
D. Iron loss in urine -> iron deficiency
E. Chronic haematuria -> blood loss

✅ Correct answer: C. Reduced erythropoietin production. In chronic kidney disease, the failing kidneys produce less erythropoietin, which is needed to stimulate red cell production. This leads to a normocytic normochromic anaemia.

A patient has bilateral renal artery stenosis. Which of the following is a likely consequence?

A. Decreased renin release
B. Increased sodium excretion
C. Systemic vasodilation
D. Secondary hyperaldosteronism
E. Increased glomerular pressure

✅ Correct answer: D. Secondary hyperaldosteronism. Reduced perfusion of the kidneys triggers renin release, activating the RAAS pathway. This leads to increased aldosterone, which promotes sodium and water retention, causing secondary hyperaldosteronism.

Which of the following findings suggests post-renal failure?

A. Enlarged kidneys on ultrasound
B. Frothy urine
C. Urinary red cell casts
D. Bilateral hydronephrosis
E. Normal urine output

✅ Correct answer: D. Bilateral hydronephrosis. Post-renal failure occurs due to obstruction after the kidneys (e.g. bladder outlet obstruction). Bilateral hydronephrosis on imaging indicates urine back-up from obstruction.

A 20-year-old man develops haematuria within 24 hours of an upper respiratory infection. Urine shows red cell casts and mild proteinuria. What is the most likely diagnosis?

A. Minimal change disease
B. IgA nephropathy
C. Lupus nephritis
D. Post-streptococcal GN
E. Diabetic nephropathy

✅ Correct answer: B. IgA nephropathy. IgA nephropathy often presents with haematuria shortly after mucosal infections (e.g., URTI). In contrast, post-streptococcal GN typically presents 1–2 weeks later.

Why does kidney disease often lead to metabolic acidosis?

A. Increased urea production
B. Excess bicarbonate reabsorption
C. Reduced acid excretion
D. Loss of chloride in urine
E. Inability to absorb water

✅ Correct answer: C. Reduced acid excretion. Healthy kidneys excrete hydrogen ions and regenerate bicarbonate. In kidney failure, this acid-handling capacity is impaired, leading to accumulation of acids and metabolic acidosis.

Which of the following most accurately reflects a key limitation of eGFR in clinical practice?

A. It cannot be used in older adults
B. It overestimates function in obese individuals
C. It underestimates function in muscular patients
D. It is unaffected by acute illness
E. It is more accurate than measured GFR

✅ Correct answer: C. It underestimates function in muscular patients. eGFR assumes average muscle mass. In muscular individuals, high creatinine levels may suggest impaired kidney function when in fact filtration is normal.

Which of the following substances is secreted into the renal tubule rather than reabsorbed?

A. Sodium
B. Glucose
C. Creatinine
D. Bicarbonate
E. Urea

✅ Correct answer: C. Creatinine. Creatinine is filtered by the glomerulus and also secreted by the tubules in small amounts. It is not reabsorbed, which is why it serves as a useful (though imperfect) marker of GFR.

Which of the following is reabsorbed in the proximal tubule and nearly completely cleared from the filtrate in a healthy individual?

A. Urea
B. Glucose
C. Potassium
D. Creatinine
E. Bicarbonate

✅ Correct answer: B. Glucose. In healthy individuals, glucose is freely filtered by the glomerulus and almost entirely reabsorbed in the proximal tubule via sodium-glucose co-transporters. Glucosuria occurs only if plasma glucose is excessively high.

Which of the following best describes the role of antidiuretic hormone (ADH) in the kidney?

A. Stimulates sodium reabsorption in the proximal tubule
B. Increases glomerular filtration
C. Promotes water reabsorption in the collecting duct
D. Inhibits aldosterone secretion
E. Promotes potassium secretion

✅ Correct answer: C. Promotes water reabsorption in the collecting duct. ADH binds to receptors in the collecting ducts, increasing water permeability via aquaporin channels. This allows water reabsorption and concentration of urine, particularly during dehydration.

A 25-year-old male is found to have microscopic haematuria following a sore throat 2 weeks ago. Which of the following best describes the underlying pathophysiology?

A. Tubular necrosis
B. Autoimmune attack on the basement membrane
C. Immune complex deposition in the glomerulus
D. Renal artery thrombosis
E. Ureteric obstruction

✅ Correct answer: C. Immune complex deposition in the glomerulus. Post-streptococcal glomerulonephritis is caused by immune complexes depositing in the glomerulus, triggering inflammation. It typically follows a streptococcal throat or skin infection.

Which of the following best describes the blood flow route into the glomerulus?

A. Peritubular capillaries → efferent arteriole → glomerulus
B. Renal vein → afferent arteriole → glomerulus
C. Afferent arteriole → glomerulus → efferent arteriole
D. Efferent arteriole → glomerulus → collecting duct
E. Glomerulus → Bowman's capsule → afferent arteriole

✅ Correct answer: C. Afferent arteriole → glomerulus → efferent arteriole. Blood enters the glomerulus via the afferent arteriole and exits through the efferent arteriole. This high-pressure system enables effective filtration into Bowman’s space.

A 4-year-old is brought in with swelling around the eyes, especially in the morning. Urine dipstick shows 4+ protein. Which of the following mechanisms best explains the oedema?

A. Sodium retention by the collecting ducts
B. Hypoalbuminaemia lowering plasma oncotic pressure
C. Increased hydrostatic pressure in the renal veins
D. Glomerular bleeding
E. Reduced water intake

✅ Correct answer: B. Hypoalbuminaemia lowering plasma oncotic pressure. Heavy protein loss in nephrotic syndrome causes hypoalbuminaemia. This reduces plasma oncotic pressure, allowing fluid to shift from blood vessels into interstitial spaces, causing oedema.

Which cell type lines the glomerular capillaries and plays a critical role in filtration?

A. Macrophages
B. Podocytes
C. Juxtaglomerular cells
D. Mesangial cells
E. Intercalated cells

✅ Correct answer: B. Podocytes. Podocytes are specialised epithelial cells that form part of the glomerular filtration barrier. Their slit diaphragms help prevent proteins and large molecules from entering the filtrate.

In a healthy nephron, where is the majority of filtered sodium reabsorbed?

A. Collecting duct
B. Distal tubule
C. Loop of Henle
D. Proximal tubule
E. Glomerulus

✅ Correct answer: D. Proximal tubule. Around 65–70% of filtered sodium is reabsorbed in the proximal tubule, along with water, glucose, and amino acids. This is a key site for bulk reabsorption.

A patient with chronic kidney disease is noted to have high serum potassium. Which of the following is the best explanation?

A. Increased aldosterone secretion
B. Reduced glomerular filtration
C. Increased potassium absorption in the gut
D. Decreased urea production
E. Excess insulin action

✅ Correct answer: B. Reduced glomerular filtration. Impaired kidney function reduces the ability to excrete potassium. This leads to hyperkalaemia, which is a common and potentially dangerous complication of kidney failure.

Which process contributes most to the concentration of urine in the loop of Henle?

A. Countercurrent multiplication
B. Active water secretion
C. Glomerular hydrostatic pressure
D. Aldosterone release
E. Tubular necrosis

✅ Correct answer: A. Countercurrent multiplication. The loop of Henle establishes a medullary concentration gradient through countercurrent multiplication. This allows the collecting duct to reabsorb water and produce concentrated urine when needed.

A patient presents with confusion. Bloods show: Na⁺ 140 mmol/L (normal), K⁺ 6.3 mmol/L (high), HCO₃⁻ 17 mmol/L (low), creatinine 320 μmol/L (elevated). Which acid–base disturbance is most likely?

A. Respiratory acidosis
B. Metabolic alkalosis
C. Metabolic acidosis
D. Respiratory alkalosis
E. Normal anion gap

✅ Correct answer: C. Metabolic acidosis. Impaired kidney function reduces acid excretion and bicarbonate regeneration. This leads to a high anion gap metabolic acidosis, often with elevated potassium.

What is the best explanation for high serum creatinine in kidney failure?

A. Increased dietary intake
B. Decreased glomerular filtration
C. Increased tubular reabsorption
D. Excess muscle breakdown
E. Increased liver production

✅ Correct answer: B. Decreased glomerular filtration. Creatinine is filtered by the glomerulus but not reabsorbed. In kidney failure, reduced GFR leads to accumulation of creatinine in the blood, making it a useful marker of renal function.

A 60-year-old with long-standing diabetes has microalbuminuria. What does this finding indicate?

A. Complete nephron loss
B. Early glomerular damage
C. Tubular necrosis
D. Bladder infection
E. Dehydration

✅ Correct answer: B. Early glomerular damage. Microalbuminuria is an early sign of diabetic nephropathy. It reflects subtle damage to the glomerular filtration barrier before overt proteinuria or a fall in eGFR is seen.

A person with dehydration is producing concentrated urine. Which part of the nephron is primarily responsible for this response?

A. Proximal tubule
B. Loop of Henle
C. Distal tubule
D. Collecting duct
E. Glomerulus

✅ Correct answer: D. Collecting duct. In response to ADH, the collecting ducts become permeable to water, allowing reabsorption down the medullary gradient. This concentrates the urine and conserves body water.

Why is it important to interpret eGFR in context of age and body size?

A. Creatinine is not produced in elderly people
B. eGFR is unaffected by muscle mass
C. Creatinine is secreted by the lungs
D. Lower muscle mass can underestimate renal function
E. eGFR overestimates function in young athletes

✅ Correct answer: D. Lower muscle mass can underestimate renal function. eGFR is estimated using serum creatinine, which is influenced by muscle mass. In elderly or frail individuals with low muscle mass, creatinine may appear low despite impaired kidney function.

Which of the following electrolyte transport processes occurs primarily in the thick ascending limb of the loop of Henle?

A. Passive water reabsorption
B. Bicarbonate secretion
C. Active reabsorption of sodium, potassium, and chloride
D. Potassium secretion
E. Calcium reabsorption via aquaporins

✅ Correct answer: C. Active reabsorption of sodium, potassium, and chloride. The thick ascending limb actively reabsorbs Na⁺, K⁺, and Cl⁻ via the Na⁺/K⁺/2Cl⁻ cotransporter (NKCC2). This segment is impermeable to water, helping to create the medullary concentration gradient essential for urine concentration.

Which of the following occurs in the distal nephron in response to aldosterone?

A. Inhibition of sodium reabsorption
B. Increased potassium reabsorption
C. Increased sodium reabsorption and potassium secretion
D. Decreased water permeability
E. Bicarbonate secretion into the tubule

✅ Correct answer: C. Increased sodium reabsorption and potassium secretion. Aldosterone acts on principal cells in the distal tubule and collecting duct to increase the activity of sodium channels (ENaC) and sodium-potassium pumps. This promotes sodium reabsorption and potassium secretion, helping regulate blood volume and potassium balance.

Which of the following best describes how parathyroid hormone (PTH) affects calcium and phosphate handling in the kidney?

A. Increases reabsorption of both calcium and phosphate
B. Decreases reabsorption of both calcium and phosphate
C. Increases calcium reabsorption and decreases phosphate reabsorption
D. Decreases calcium reabsorption and increases phosphate reabsorption
E. Has no significant effect on electrolyte handling in the kidney

✅ Correct answer: C. Increases calcium reabsorption and decreases phosphate reabsorption. PTH increases calcium reabsorption in the distal tubule while decreasing phosphate reabsorption in the proximal tubule. This helps raise serum calcium levels and lower phosphate, maintaining balance when serum calcium is low or phosphate is high.

A 65-year-old man with chronic kidney disease has a GFR of 18 mL/min/1.73m² (reduced)
. He is fatigued and has bone pain. Labs show: phosphate ↑, calcium ↓, PTH ↑. What is the most likely underlying mechanism for his bone pain?

A. Direct calcium loss in the urine
B. Reduced vitamin D activation by the kidney
C. Phosphate binding excess calcium in the gut
D. Increased intestinal calcium absorption
E. Elevated aldosterone increasing calcium loss

✅ Correct answer: B. Reduced vitamin D activation by the kidney. The kidney converts inactive vitamin D into calcitriol. In CKD, this step is impaired, leading to reduced calcium absorption from the gut and secondary hyperparathyroidism, which promotes bone resorption — the cause of renal osteodystrophy and bone pain.

A 28-year-old man presents with haemoptysis and haematuria. Urine shows red cell casts, and creatinine is elevated. Chest X-ray reveals pulmonary infiltrates. Which of the following best describes the pathogenesis of his condition?

A. Immune complex deposition in glomeruli
B. Direct infection of glomerular basement membrane
C. T-cell mediated injury to alveolar capillaries
D. Autoantibodies targeting type IV collagen in basement membranes
E. Deposition of amyloid in alveolar and glomerular vessels

✅ Correct answer: D. Autoantibodies targeting type IV collagen in basement membranes. Goodpasture’s syndrome is caused by anti-GBM antibodies that target type IV collagen in both glomerular and alveolar basement membranes. This leads to pulmonary haemorrhage and rapidly progressive glomerulonephritis with red cell casts and renal failure.

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