Tubular Reabsorption: Mechanisms and Selectivity
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Questions and Answers

Which of the following accurately describes the relationship between creatinine excretion and GFR in a healthy individual?

  • Creatinine excretion rate is inversely proportional to GFR.
  • Creatinine excretion rate is directly proportional to GFR. (correct)
  • Creatinine excretion rate is independent of GFR.
  • Creatinine excretion rate is significantly higher than GFR.

    • What is the main reason why creatinine is a useful marker for assessing GFR?

  • It is secreted in large quantities by the tubules.
  • It is completely cleared from the plasma by glomerular filtration. (correct)
  • It is readily reabsorbed by the tubules.
  • It is an essential nutrient required for cellular function.

    • According to the passage, how can you estimate changes in GFR using creatinine measurements?

  • By measuring the rate of creatinine secretion by the tubules.
  • By comparing the creatinine concentration in urine and plasma. (correct)
  • By studying the rate of creatinine reabsorption by the tubules.
  • By analyzing the amount of creatinine excreted in urine.

    • Assuming a substance is completely cleared from the plasma, what does this suggest regarding its excretion?

    <p>It is excreted entirely through tubular secretion. (C)</p> Signup and view all the answers

    If the rate of creatinine excretion is less than the rate of glomerular filtration, what does this suggest?

    <p>Tubular reabsorption of creatinine. (D)</p> Signup and view all the answers

    What does active transport move solutes against?

    <p>Electrochemical gradient (B)</p> Signup and view all the answers

    What is an example of a pump involved in active transport?

    <p>Sodium-potassium ATPase (D)</p> Signup and view all the answers

    What primarily influences sodium transport in the proximal tubule?

    <p>Concentration gradient and time (B)</p> Signup and view all the answers

    How is secondary active transport primarily mediated?

    <p>Ion gradients (B)</p> Signup and view all the answers

    What effect does aldosterone have on transport maximums?

    <p>It increases transport maximums (B)</p> Signup and view all the answers

    What role do tight junctions play in epithelial cells?

    <p>Holding cells together (B)</p> Signup and view all the answers

    How does water permeability in the distal tubules compare to that in the proximal tubule?

    <p>Lower in the distal tubules (C)</p> Signup and view all the answers

    What occurs during venous reabsorption?

    <p>Hydrostatic and colloid osmotic pressures allow solute transfer (B)</p> Signup and view all the answers

    What substance greatly increases the water permeability in distal and collecting tubules?

    <p>Antidiuretic hormone (ADH) (D)</p> Signup and view all the answers

    What happens to sodium during secondary active transport involving glucose?

    <p>Sodium is absorbed along with glucose (C)</p> Signup and view all the answers

    What occurs to solute concentrations inside the tubule when solutes are transported out?

    <p>They decrease, allowing more reabsorption (D)</p> Signup and view all the answers

    What primarily mediates the transport of solutes across tubular capillary walls?

    <p>Hydrostatic and colloid osmotic pressures (C)</p> Signup and view all the answers

    What is the effect of the sodium-potassium ATPase pump on intracellular sodium concentration?

    <p>Decreases intracellular sodium concentration (C)</p> Signup and view all the answers

    Which segment of the nephron exhibits low water permeability due to tight junctions?

    <p>Loop of Henle (D)</p> Signup and view all the answers

    What primarily dictates the rate of transport in the proximal tubule?

    <p>Tubular flow rate (A)</p> Signup and view all the answers

    What happens to sodium when there are higher concentrations in the tubular lumen?

    <p>More sodium is reabsorbed (B)</p> Signup and view all the answers

    What components are needed to calculate net filtration pressure?

    <p>Capillary pressure, interstitial hydrostatic pressure, capillary colloid pressure, and interstitial fluid colloid pressure (B)</p> Signup and view all the answers

    Which of the following describes how an increase in arterial pressure affects peri tubular capillary reabsorption?

    <p>It decreases reabsorption by raising peri tubular capillary hydrostatic pressure (D)</p> Signup and view all the answers

    What is the result of increased resistance in afferent arterioles on peri tubular capillary pressure?

    <p>Decreases peri tubular capillary hydrostatic pressure (B)</p> Signup and view all the answers

    Which pressure increases peri tubular capillary absorption according to the provided information?

    <p>Capillary colloid osmotic pressure (B)</p> Signup and view all the answers

    If capillary pressure is 13 and interstitial pressure is 6, what is the net filtration pressure component from these values?

    <p>7 (B)</p> Signup and view all the answers

    What overall effect does raising plasma protein concentration in systemic blood have?

    <p>Increases tubular capillary colloid osmotic pressure (B)</p> Signup and view all the answers

    The filtration coefficient is influenced by what two main factors?

    <p>Hydraulic conductivity and surface area of capillaries (C)</p> Signup and view all the answers

    A net reabsorption of ten occurs under which combination of pressures?

    <p>13 capillary pressure and 6 interstitial hydrostatic pressure, along with osmotic pressures (C)</p> Signup and view all the answers

    What is the primary action of Atrial Natriuretic Peptide (ANP)?

    <p>Decrease sodium and water reabsorption by renal tubules. (C)</p> Signup and view all the answers

    In congestive heart failure, what happens to the levels of ANP?

    <p>They increase dramatically. (B)</p> Signup and view all the answers

    What effect does sympathetic stimulation have on the kidneys?

    <p>Activates alpha adrenergic receptors. (B)</p> Signup and view all the answers

    What is renal clearance a measure of?

    <p>The volume of plasma cleared of a substance by the kidneys over time. (D)</p> Signup and view all the answers

    What is the role of parathyroid hormone in the renal system?

    <p>Increase reabsorption of calcium and magnesium. (B)</p> Signup and view all the answers

    What can be concluded about substances that are freely filtered but not reabsorbed or secreted?

    <p>Their urinary excretion rate equals the filtration rate. (D)</p> Signup and view all the answers

    Which statement about inulin is true in the context of GFR measurement?

    <p>It can be used as an indicator since it is not reabsorbed or secreted. (C)</p> Signup and view all the answers

    Creatinine is cleared from the body primarily through which process?

    <p>Glomerular filtration. (D)</p> Signup and view all the answers

    What is the process by which large molecules like proteins are reabsorbed from the tubular lumen?

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

    Which of the following substances is reabsorbed almost completely from the tubular lumen?

    <p>Glucose (A)</p> Signup and view all the answers

    What is the primary factor determining the amount of a substance filtered by the glomerulus?

    <p>The concentration of the substance in the plasma (D)</p> Signup and view all the answers

    Which of these factors can cause a large change in urinary excretion?

    <p>A small change in tubular reabsorption (C)</p> Signup and view all the answers

    What is the mechanism by which substances are reabsorbed from the tubular lumen back into the blood?

    <p>Active or passive transport (B)</p> Signup and view all the answers

    What is the role of the brush border in protein reabsorption?

    <p>It helps to bind proteins to the tubular epithelium (A)</p> Signup and view all the answers

    What is the role of the renal interstitium in tubular reabsorption?

    <p>It provides a pathway for the reabsorption of substances (B)</p> Signup and view all the answers

    Which of the following is NOT a characteristic of tubular reabsorption?

    <p>Always involves active transport (D)</p> Signup and view all the answers

    Study Notes

    Tubular Reabsorption

    • Reabsorption in the proximal tubule, especially, involves pinocytosis for large molecules like proteins
    • Proteins are digested into amino acids, then reabsorbed via the basal lateral membrane
    • This process requires energy, considered active transport
    • Filtration is non-selective, meaning substances not bound to proteins are filtered
    • The amount filtered depends on plasma concentration
    • Tubular reabsorption is highly selective, some substances (glucose, amino acids) are reabsorbed almost completely, while others (sodium, chloride) vary based on body needs
    • Waste products (urea) are poorly reabsorbed and excreted in large amounts
    • Reabsorption mechanisms include transcellular (across cells) and paracellular (between cells) pathways, require movement from tubular lumen to renal interstitial fluid, then blood
    • Mechanism is controlled independently for different substances, allowing selective reabsorption and secretion
    • Active transport moves solutes against gradients, needing energy; an example is the sodium-potassium ATPase pump
    • Sodium-potassium ATPase moves sodium out of the cell & potassium into, against their electrochemical gradients
    • Secondary active transport couples with an existing gradient (e.g., sodium gradient); glucose and amino acids are examples using sodium-coupled transport
    • Concentration gradients drive passive movement, important for solute reabsorption, e.g., glucose

    Epithelial Cells and Transport Mechanisms

    • Epithelial cells are bound by tight junctions, allowing for transcellular (through cells) and paracellular (between cells) transport paths
    • Primary active transport moves substances against electrochemical gradients (e.g., sodium potassium pump) utilizing ATP, and is crucial for establishing gradients
    • Secondary active transport couples with existing gradients (e.g., sodium gradient); examples include glucose and amino acid transport.
    • Filtration and reabsorption create strong concentration gradients that are essential for driving substances across the membranes of the tubule and interstitial fluid
    • The concentration of solutes within tubular fluid and the renal interstitium influences the direction, mechanism, and rate of solute transport, crucial for maintaining homeostasis

    Transport Maximum and Regulation

    • Transport maximum (Tm) is the theoretical upper limit for reabsorption of specific substances (e.g., glucose) by the tubules
    • Exceeding the transport maximum results in the excretion of that substance, e.g., glucose in urine
    • Sodium reabsorption mechanisms greatly exceed the sodium filtration rate
    • Rate of sodium reabsorption is influenced by gradient and time, not a maximum
    • This is in contrast to substances whose reabsorption is determined by others factors
    • Hormonal regulation (e.g., aldosterone) greatly affects sodium reabsorption (and other important mechanisms)

    Water and Solute Reabsorption

    • Water reabsorption is highly regulated and occurs predominantly through aquaporins (water channels) in the cell membranes and tight junctions
    • Water reabsorption is significant along the proximal tubules and descending loop of Henle
    • Water permeability in different parts of the nephron varies, crucial for water re-absorption and urine concentration
    • Chloride reabsorption is often linked to sodium and thus passively driven by electrical gradients
    • Urea reabsorption is lower than chloride, and its concentration increases with continued water reabsorption
    • Waste products (creatinine) are not reabsorbed

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    Related Documents

    Renal Tubular Reabsorption and Secretion PDF

    Description

    This quiz explores the intricate processes of tubular reabsorption, focusing on the proximal tubule's role in reabsorbing essential molecules like amino acids and glucose. It covers active transport mechanisms, the selectivity of reabsorption, and how various substances are filtered and processed in the kidneys. Test your understanding of these vital renal functions!

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