Urine Concentration and Dilution Chapter 29
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Questions and Answers

What is the lowest osmolarity of urine that the kidneys can excrete?

  • 50 mOsm/L (correct)
  • 200 mOsm/L
  • 300 mOsm/L
  • 100 mOsm/L

    • What happens to the tubular fluid in the ascending loop of Henle and early distal tubule?

  • It becomes hypertonic
  • It becomes hypo-osmotic (correct)
  • It remains isosmotic
  • It becomes isotonic

    • What is necessary for forming a concentrated urine?

  • High level of ADH (correct)
  • Low osmolarity of the renal medullary interstitial fluid
  • Low level of ADH
  • High volume of urine production

    • What contributes to the buildup of solute concentration in the renal medullary interstitium?

    <p>Active transport of ions from the collecting ducts into the medullary interstitium and facilitated diffusion of urea from the inner medullary collecting ducts</p> Signup and view all the answers

    What happens to the tubular fluid in the late distal and collecting tubules and medullary collecting duct in the absence of ADH?

    <p>It becomes more hypo-osmotic</p> Signup and view all the answers

    What is the highest osmolarity of urine that the kidneys can excrete?

    <p>1400 mOsm/L</p> Signup and view all the answers

    What happens to the tubular fluid as it passes down the descending loop of Henle?

    <p>It becomes hypertonic</p> Signup and view all the answers

    What is necessary for the formation of dilute urine?

    <p>Low level of ADH</p> Signup and view all the answers

    What is the primary function of the Na/K/2Cl pump in the nephron?

    <p>Establish a 200-mOsm/L concentration gradient</p> Signup and view all the answers

    Which of the following is NOT a factor contributing to the preservation of high osmolarity in the renal medullary interstitium?

    <p>High blood flow in the medulla</p> Signup and view all the answers

    What is the purpose of the vasa recta in the renal medulla?

    <p>To facilitate countercurrent exchange and minimize solute loss</p> Signup and view all the answers

    What is the approximate percentage of total renal blood flow that goes to the medulla?

    <p>5%</p> Signup and view all the answers

    What is the result of large amounts of water being reabsorbed into the cortex rather than the medulla?

    <p>Minimized solute loss from the medullary interstitium</p> Signup and view all the answers

    What is the main benefit of the sluggish blood flow in the medulla?

    <p>Minimized solute loss from the medullary interstitium</p> Signup and view all the answers

    What is the primary function of the Na/K/2Cl pump in the nephron?

    <p>To establish a concentration gradient between the tubular lumen and interstitial fluid</p> Signup and view all the answers

    What is the effect of countercurrent exchange in the vasa recta?

    <p>To minimize the washout of solutes from the medullary interstitium</p> Signup and view all the answers

    What is the result of medullary blood flow being low?

    <p>To minimize the solute loss from the medullary interstitium</p> Signup and view all the answers

    What is the effect of large amounts of water being reabsorbed into the cortex rather than the medulla?

    <p>To preserve the high osmolarity of the renal medullary interstitial fluid</p> Signup and view all the answers

    What is the role of urea recirculation in the kidney?

    <p>To maintain the high osmolarity of the renal medullary interstitial fluid</p> Signup and view all the answers

    What is the countercurrent multiplier system responsible for?

    <p>Preserving the high osmolarity of the renal medullary interstitial fluid</p> Signup and view all the answers

    What is the function of ADH in the formation of concentrated urine?

    <p>To increase the permeability of the late distal tubules and collecting ducts to water</p> Signup and view all the answers

    What happens to the tubular fluid as it passes through the proximal tubules?

    <p>It remains isosmotic</p> Signup and view all the answers

    What is the purpose of urea recirculation in the renal medulla?

    <p>To facilitate the buildup of solute concentration in the renal medullary interstitium</p> Signup and view all the answers

    What is the result of the kidneys excreting highly concentrated urine?

    <p>Body fluid osmolarity is increased</p> Signup and view all the answers

    What is the role of the countercurrent multiplier system in the renal medulla?

    <p>To facilitate the buildup of solute concentration in the renal medullary interstitium</p> Signup and view all the answers

    What happens to the tubular fluid as it passes through the ascending loop of Henle?

    <p>It becomes hypotonic</p> Signup and view all the answers

    What is the primary function of the kidneys in regulating body fluid osmolarity?

    <p>To vary the relative proportions of solutes and water in the urine</p> Signup and view all the answers

    What is the maximum daily urine output of the kidneys when the body has excess water?

    <p>Up to 20 liter/day</p> Signup and view all the answers

    Study Notes

    Urine Concentration and Dilution

    • Normal kidneys can vary the relative proportions of solutes and water in the urine in response to various challenges.
    • The kidneys can excrete urine with an osmolarity as low as 50 mOsm/L (diluted urine) when there is excess water in the body and body fluid osmolarity is reduced.
    • The kidneys can excrete highly concentrated urine with an osmolarity of 1200 to 1400 mOsm/L when there is a deficit of water in the body and extracellular fluid osmolarity is high.

    Formation of Dilute Urine

    • Tubular fluid remains isosmotic in proximal tubules.
    • As fluid passes down the descending loop of Henle, water is reabsorbed by osmosis, and the tubular fluid becomes hypertonic.
    • Tubular fluid is diluted (hypo-osmotic) in the ascending loop of Henle and early distal tubule, regardless of whether ADH is present or absent.
    • Tubular fluid in late distal and collecting tubules and medullary collecting duct is further diluted (more hypo-osmotic) in the absence of ADH.

    Formation of Concentrated Urine

    • Two basic requirements for forming a concentrated urine are:
      • High level of ADH, which increases the permeability of the late distal tubules, cortical and medullary collecting ducts to water.
      • High osmolarity (high solute concentration) of the renal medullary interstitial fluid.

    High Osmolarity of the Renal Medullary Interstitial Fluid

    • Major factors that contribute to the buildup of solute concentration into the medulla include:
      • Active transport of Na ions and co-transport of K, Cl, and other ions out of the thick ascending limb of the loop of Henle (Countercurrent multiplier system).
      • Active transport of ions from the collecting ducts into the medullary interstitium.
      • Facilitated diffusion of urea from the inner medullary collecting ducts (urea recirculation).
      • Diffusion of only small amounts of water into the medullary interstitium—far less than the reabsorption of solutes.

    Preservation of High Osmolarity

    • Two special features of the renal medullary blood flow (vasa recta) that contribute to preserving high osmolarity into the medulla:
      • The vasa recta serve as countercurrent exchangers, minimizing the washout of solutes from the medullary interstitium.
      • Large amounts of water are reabsorbed into the cortex, rather than into the renal medulla.
      • Medullary blood flow is low (less than 5% of the total RBF), which is sufficient to supply the metabolic needs of the tissues but helps minimize solute loss from the medullary interstitium.

    Urine Concentration and Dilution

    • Normal kidneys can vary the relative proportions of solutes and water in the urine in response to various challenges.
    • The kidneys can excrete urine with an osmolarity as low as 50 mOsm/L (diluted urine) when there is excess water in the body and body fluid osmolarity is reduced.
    • The kidneys can excrete highly concentrated urine with an osmolarity of 1200 to 1400 mOsm/L when there is a deficit of water in the body and extracellular fluid osmolarity is high.

    Formation of Dilute Urine

    • Tubular fluid remains isosmotic in proximal tubules.
    • As fluid passes down the descending loop of Henle, water is reabsorbed by osmosis, and the tubular fluid becomes hypertonic.
    • Tubular fluid is diluted (hypo-osmotic) in the ascending loop of Henle and early distal tubule, regardless of whether ADH is present or absent.
    • Tubular fluid in late distal and collecting tubules and medullary collecting duct is further diluted (more hypo-osmotic) in the absence of ADH.

    Formation of Concentrated Urine

    • Two basic requirements for forming a concentrated urine are:
      • High level of ADH, which increases the permeability of the late distal tubules, cortical and medullary collecting ducts to water.
      • High osmolarity (high solute concentration) of the renal medullary interstitial fluid.

    High Osmolarity of the Renal Medullary Interstitial Fluid

    • Major factors that contribute to the buildup of solute concentration into the medulla include:
      • Active transport of Na ions and co-transport of K, Cl, and other ions out of the thick ascending limb of the loop of Henle (Countercurrent multiplier system).
      • Active transport of ions from the collecting ducts into the medullary interstitium.
      • Facilitated diffusion of urea from the inner medullary collecting ducts (urea recirculation).
      • Diffusion of only small amounts of water into the medullary interstitium—far less than the reabsorption of solutes.

    Preservation of High Osmolarity

    • Two special features of the renal medullary blood flow (vasa recta) that contribute to preserving high osmolarity into the medulla:
      • The vasa recta serve as countercurrent exchangers, minimizing the washout of solutes from the medullary interstitium.
      • Large amounts of water are reabsorbed into the cortex, rather than into the renal medulla.
      • Medullary blood flow is low (less than 5% of the total RBF), which is sufficient to supply the metabolic needs of the tissues but helps minimize solute loss from the medullary interstitium.

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    Description

    This quiz covers the kidney's ability to regulate urine concentration and dilution in response to changes in body fluid osmolarity. Learn about the range of urine osmolarity and how it adapts to excess or deficit of water in the body.

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