Renal Physiology: Glomerular Filtration and Tubular Reabsorption
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Questions and Answers

What is the formula for urinary excretion rate?

  • Filtration rate - Reabsorption rate + Secretion rate (correct)
  • Filtration rate + Reabsorption rate + Secretion rate
  • Reabsorption rate - Filtration rate + Secretion rate
  • Filtration rate + Secretion rate - Reabsorption rate

    • What is the assumed condition for the filtration calculation of a substance?

  • The substance is only filtered through the glomerulus
  • The substance is freely filtered and not bound to plasma proteins (correct)
  • The substance is not freely filtered
  • The substance is bound to plasma proteins

    • What is the main difference between GFR and tubular reabsorption?

  • One is active and the other is passive
  • One is selective and the other is non-selective (correct)
  • One is complex and the other is simple
  • One is fast and the other is slow

    • What is required for a substance to be reabsorbed?

    <p>It must be transported across the tubular epithelial membranes into the renal interstitial fluid</p> Signup and view all the answers

    What type of transport is involved in reabsorption?

    <p>Both passive and active transport</p> Signup and view all the answers

    What percentage of the filtered load of sodium and water is normally reabsorbed?

    <p>About 65%</p> Signup and view all the answers

    Which substances are reabsorbed in the proximal tubule?

    <p>Glucose, amino acids, sodium, and water</p> Signup and view all the answers

    What is the characteristic of reabsorption in the proximal tubule?

    <p>High capacity for active and passive reabsorption</p> Signup and view all the answers

    What is the main function of the paracellular pathway in the proximal tubule?

    <p>Reabsorption of glucose and amino acid</p> Signup and view all the answers

    What is the purpose of secretion of H+ in the proximal tubule?

    <p>To remove excess hydrogen ions from the blood</p> Signup and view all the answers

    What determines the transport maximum (Tm) for substances in the proximal tubule?

    <p>All of the above</p> Signup and view all the answers

    What is the significance of the threshold for glucose in the proximal tubule?

    <p>It is the amount of glucose above which it starts to appear in the urine</p> Signup and view all the answers

    In which part of the nephron do the epithelial cells have much tighter junctions?

    <p>Distal parts of the nephron</p> Signup and view all the answers

    What is the characteristic of the thin descending segment of the loop of Henle?

    <p>Highly permeable to water and moderately permeable to solutes</p> Signup and view all the answers

    What is the function of the aldosterone hormone in the nephron?

    <p>To increase the transport maximum for sodium reabsorption</p> Signup and view all the answers

    What is the main difference between the transport of glucose and sodium in the proximal tubule?

    <p>Glucose exhibits a transport maximum, while sodium does not</p> Signup and view all the answers

    What is the primary function of reabsorption in the kidney?

    <p>To reabsorb essential nutrients and ions</p> Signup and view all the answers

    What determines the amount of a substance filtered by the kidneys?

    <p>The glomerular filtration rate (GFR)</p> Signup and view all the answers

    What is the main difference between glomerular filtration and tubular reabsorption?

    <p>Filtration is non-selective, while reabsorption is selective</p> Signup and view all the answers

    What is the primary mechanism of reabsorption in the proximal tubule?

    <p>Active transport</p> Signup and view all the answers

    What is the main function of the proximal tubule?

    <p>To reabsorb essential nutrients and ions</p> Signup and view all the answers

    What is the effect of a small change in glomerular filtration or tubular reabsorption?

    <p>A large change in urinary excretion</p> Signup and view all the answers

    What is the significance of the coordinated regulation of glomerular filtration and tubular reabsorption?

    <p>To avoid large fluctuations in urinary excretion</p> Signup and view all the answers

    What is the characteristic of tubular reabsorption in the proximal tubule?

    <p>High capacity for active and passive reabsorption</p> Signup and view all the answers

    What is the primary function of the paracellular pathway in the proximal tubule?

    <p>Reabsorption of sodium and chloride</p> Signup and view all the answers

    Which substances are reabsorbed in the first half of the proximal tubule?

    <p>Glucose and amino acid</p> Signup and view all the answers

    What is the purpose of the secretion of H+ in the proximal tubule?

    <p>To regulate tubular fluid pH</p> Signup and view all the answers

    What determines the transport maximum for substances in the proximal tubule?

    <p>Electrochemical gradient and time</p> Signup and view all the answers

    What is the characteristic of the transport of glucose in the proximal tubule?

    <p>Active transport with a transport maximum</p> Signup and view all the answers

    What is the function of the thin descending segment of the loop of Henle?

    <p>Reabsorption of water and urea</p> Signup and view all the answers

    What is the effect of aldosterone on sodium reabsorption in the distal parts of the nephron?

    <p>Increases sodium reabsorption</p> Signup and view all the answers

    What is the significance of the threshold for glucose in the proximal tubule?

    <p>It is the plasma concentration of glucose below which glucose is not reabsorbed</p> Signup and view all the answers

    Study Notes

    Kidney Function and Reabsorption

    • Urinary excretion rate is calculated as Filtration rate - Reabsorption rate + Secretion rate
    • Filtration of a substance is calculated as GFR × plasma concentration (e.g., Filtration of Glucose = 180 L/day × 1 g/L = 180 gr/day)

    Importance of Reabsorption

    • Small changes in glomerular filtration or tubular reabsorption can cause large changes in urinary excretion
    • Changes in tubular reabsorption and glomerular filtration are closely coordinated to avoid large fluctuations in urinary excretion

    Types of Transport

    • Active transport: primary active, secondary active
    • Passive transport: diffusion (simple, facilitated), osmosis, pinocytosis

    Reabsorption and Secretion in Proximal Tubule (PT)

    • Normally, 65% of filtered load of sodium and water, and a slightly lower percentage of filtered chloride are reabsorbed
    • Reabsorbs all filtered glucose and amino acids
    • High capacity for active and passive reabsorption through transcellular and paracellular pathways
    • Reabsorption of glucose and amino acid especially in the first half of PT
    • Reabsorption of Na in 3 steps
    • Reabsorption of Cl especially in the 2nd half of PT
    • Secretion of organic acids and bases, including bile salts, oxalate, catecholamines, and hydrogen

    Transport Maximum (Tm)

    • Tm for substances that are actively reabsorbed or secreted
    • Example: Glucose transport system in the proximal tubule (GFR × plasma glucose = 125 ml/min × 1 mg/ml = 125 mg/min)
    • Threshold for Glucose: ~ 250 mg/min
    • Tm for glucose: ~ 375 mg/min
    • Substances that are passively transported do not exhibit a Tm
    • Substances that are actively transported but do not exhibit a Tm, such as reabsorption of Na in PT

    Kidney Function and Reabsorption

    • Urinary excretion rate is calculated as Filtration rate - Reabsorption rate + Secretion rate
    • Filtration of a substance is calculated as GFR × plasma concentration (e.g., Filtration of Glucose = 180 L/day × 1 g/L = 180 gr/day)

    Importance of Reabsorption

    • Small changes in glomerular filtration or tubular reabsorption can cause large changes in urinary excretion
    • Changes in tubular reabsorption and glomerular filtration are closely coordinated to avoid large fluctuations in urinary excretion

    Types of Transport

    • Active transport: primary active, secondary active
    • Passive transport: diffusion (simple, facilitated), osmosis, pinocytosis

    Reabsorption and Secretion in Proximal Tubule (PT)

    • Normally, 65% of filtered load of sodium and water, and a slightly lower percentage of filtered chloride are reabsorbed
    • Reabsorbs all filtered glucose and amino acids
    • High capacity for active and passive reabsorption through transcellular and paracellular pathways
    • Reabsorption of glucose and amino acid especially in the first half of PT
    • Reabsorption of Na in 3 steps
    • Reabsorption of Cl especially in the 2nd half of PT
    • Secretion of organic acids and bases, including bile salts, oxalate, catecholamines, and hydrogen

    Transport Maximum (Tm)

    • Tm for substances that are actively reabsorbed or secreted
    • Example: Glucose transport system in the proximal tubule (GFR × plasma glucose = 125 ml/min × 1 mg/ml = 125 mg/min)
    • Threshold for Glucose: ~ 250 mg/min
    • Tm for glucose: ~ 375 mg/min
    • Substances that are passively transported do not exhibit a Tm
    • Substances that are actively transported but do not exhibit a Tm, such as reabsorption of Na in PT

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    Description

    Learn about the processes of glomerular filtration, tubular reabsorption, and secretion in the kidney, including the importance of reabsorption and how to calculate filtration rates.

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