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Renal and Fluid-Electrolyte Physiology

Urine Concentration and Dilution Practice Questions

20 free Urine Concentration and Dilution practice questions for the Physiology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.

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Question 1 of 20 Medium

The primary mechanism responsible for urine concentration in the kidney is the:

  1. A Bulk glomerular filtration at the corpuscle
  2. B Countercurrent multiplication system
  3. C Active distal tubular secretion
  4. D Pressure natriuresis in the medulla

Correct answer: Countercurrent multiplication system

Countercurrent multiplication in the loop of Henle creates a hyperosmotic medullary interstitium. This gradient allows water reabsorption and urine concentration.

Question 2 of 20 Medium

Which segment of the nephron is impermeable to water but actively transports sodium chloride?

  1. A Proximal convoluted tubule
  2. B Descending limb of loop of Henle
  3. C Ascending limb of loop of Henle
  4. D Collecting duct

Correct answer: Ascending limb of loop of Henle

The thick ascending limb actively reabsorbs sodium chloride but is impermeable to water. This property is essential for generating the medullary osmotic gradient.

Question 3 of 20 Medium

The descending limb of the loop of Henle is characterized by:

  1. A Active sodium reabsorption
  2. B Impermeability to water
  3. C High permeability to water
  4. D Active urea secretion

Correct answer: High permeability to water

The descending limb is highly permeable to water but not to solutes. Water exits into the hyperosmotic medulla, concentrating tubular fluid.

Question 4 of 20 Medium

Antidiuretic hormone (ADH) primarily increases water permeability in the:

  1. A Proximal tubule
  2. B Descending limb
  3. C Distal convoluted tubule
  4. D Collecting duct

Correct answer: Collecting duct

ADH acts on the collecting ducts to insert aquaporin-2 channels. This increases water reabsorption and concentrates urine.

Question 5 of 20 Medium

In the absence of ADH, the kidney produces urine that is:

  1. A Hypertonic
  2. B Isotonic
  3. C Hypotonic
  4. D Protein-rich

Correct answer: Hypotonic

Without ADH, collecting ducts are impermeable to water. Dilute, hypotonic urine is excreted.

Question 6 of 20 Medium

Which substance contributes significantly to the medullary osmotic gradient?

  1. A Glucose
  2. B Creatinine
  3. C Urea
  4. D Calcium

Correct answer: Urea

Urea contributes substantially to medullary hypertonicity, especially in the inner medulla. Urea recycling enhances urine concentration.

Question 7 of 20 Medium

Urea recycling mainly occurs between the:

  1. A Proximal tubule and loop of Henle
  2. B Ascending limb and distal tubule
  3. C Collecting duct and loop of Henle
  4. D Glomerulus and proximal tubule

Correct answer: Collecting duct and loop of Henle

Urea diffuses from the inner medullary collecting duct into the loop of Henle. This recycling maintains high medullary osmolality.

Question 8 of 20 Medium

The countercurrent exchanger function is performed by the:

  1. A Loop of Henle
  2. B Distal tubule
  3. C Vasa recta
  4. D Collecting duct

Correct answer: Vasa recta

The vasa recta preserves the medullary osmotic gradient. It allows passive exchange of water and solutes without washout.

Question 9 of 20 Medium

Which condition results from deficiency of ADH?

  1. A SIADH
  2. B Nephrotic syndrome
  3. C Diabetes insipidus
  4. D Acute glomerulonephritis

Correct answer: Diabetes insipidus

Diabetes insipidus occurs due to lack of ADH or renal resistance to it. This leads to excretion of large volumes of dilute urine.

Question 10 of 20 Medium

Central diabetes insipidus is caused by:

  1. A Renal insensitivity to ADH
  2. B Excess ADH secretion
  3. C Deficient ADH secretion
  4. D Excess aldosterone secretion

Correct answer: Deficient ADH secretion

Central diabetes insipidus results from inadequate ADH production or release. This prevents proper water reabsorption.

Question 11 of 20 Medium

Nephrogenic diabetes insipidus is characterized by:

  1. A Normal ADH with renal unresponsiveness
  2. B Deficient secretion of ADH from the pituitary
  3. C Excess ADH secretion causing water retention
  4. D Enhanced water reabsorption in collecting ducts

Correct answer: Normal ADH with renal unresponsiveness

In nephrogenic diabetes insipidus, ADH levels are normal. The kidneys fail to respond to ADH.

Question 12 of 20 Medium

Syndrome of inappropriate ADH secretion (SIADH) leads to:

  1. A Dilute urine with elevated plasma sodium levels
  2. B Concentrated urine and hyponatremia
  3. C Polyuria and progressive dehydration
  4. D Reduced circulating plasma volume

Correct answer: Concentrated urine and hyponatremia

Excess ADH causes increased water reabsorption. This results in concentrated urine and dilutional hyponatremia.

Question 13 of 20 Medium

Maximum urine concentration depends most on:

  1. A Glomerular filtration rate
  2. B Medullary osmotic gradient
  3. C Tubular secretion rate
  4. D Renal blood flow

Correct answer: Medullary osmotic gradient

A steep medullary osmotic gradient is essential for maximal urine concentration. It drives water reabsorption from the collecting ducts.

Question 14 of 20 Medium

Which hormone increases urea permeability in the inner medullary collecting duct?

  1. A Aldosterone
  2. B Renin
  3. C ADH
  4. D Angiotensin II

Correct answer: ADH

ADH increases urea transporter activity in the inner medullary collecting duct. This enhances urea recycling.

Question 15 of 20 Medium

During water deprivation, urine osmolality:

  1. A Decreases
  2. B Remains unchanged
  3. C Increases
  4. D Becomes isotonic to plasma

Correct answer: Increases

Water deprivation increases ADH secretion. This leads to increased urine concentration.

Question 16 of 20 Medium

Which factor reduces the kidney's ability to concentrate urine?

  1. A Persistently high circulating ADH levels
  2. B A fully intact and functional loop of Henle
  3. C Reduced medullary blood flow
  4. D Damage to the loop of Henle

Correct answer: Damage to the loop of Henle

Damage to the loop of Henle disrupts countercurrent multiplication. This impairs formation of the medullary gradient.

Question 17 of 20 Medium

Free water clearance is positive when urine is:

  1. A Hypertonic
  2. B Isotonic
  3. C Hypotonic
  4. D Protein-rich

Correct answer: Hypotonic

Positive free water clearance indicates excretion of water in excess of solute. This occurs when urine is dilute.

Question 18 of 20 Medium

Which nephron segment is responsible for fine-tuning urine dilution?

  1. A Proximal tubule
  2. B Thin descending limb
  3. C Thick ascending limb
  4. D Collecting duct

Correct answer: Collecting duct

The collecting duct adjusts water reabsorption under ADH control. It determines final urine concentration.

Question 19 of 20 Medium

Loop diuretics impair urine concentration by inhibiting:

  1. A Aquaporin channels
  2. B Na-K-2Cl transporter
  3. C Sodium-glucose cotransporter
  4. D Urea transporters

Correct answer: Na-K-2Cl transporter

Loop diuretics block the Na-K-2Cl transporter in the thick ascending limb. This disrupts the medullary osmotic gradient.

Question 20 of 20 Medium

The maximum concentrating ability of human kidneys produces urine osmolality of approximately:

  1. A About 300 mOsm/kg
  2. B About 600 mOsm/kg
  3. C About 900 mOsm/kg
  4. D About 1200 mOsm/kg

Correct answer: About 1200 mOsm/kg

Human kidneys can concentrate urine up to about 1200 mOsm/kg. This depends on intact countercurrent mechanisms and ADH action.

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