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Questions and Answers

Which mechanism is responsible for the reabsorption of many solutes coupled to Na+?

  • Facilitated diffusion
  • Osmosis
  • Secondary active transport (correct)
  • Simple diffusion

    • What is the term used to describe the convoluted portion of the distal tubule?

  • Concentrating segment
  • Balancing segment
  • Diluting segment (correct)
  • Equilibrating segment

    • Where is the NKCC2 transporter located and what is its contribution?

  • Distal convoluted tubule, secretion of hydrogen ions
  • Descending limb of loop of Henle, reabsorption of sodium
  • Proximal tubule, reabsorption of water
  • Ascending limb of loop of Henle, reabsorption of sodium, potassium, and chloride (correct)

    • Which cells are responsible for the reabsorption and secretion in the late distal and cortical collecting ducts?

    <p>Intercalated cells, responsible for secretion</p> Signup and view all the answers

    Which transporter is responsible for transporting 90% of the glucose reabsorbed in the early proximal tubule?

    <p>SGLT2</p> Signup and view all the answers

    What is the main function of the thin descending limb of the Loop of Henle?

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

    Which transporter is inhibited by loop diuretics like furosemide in the thick ascending limb of the Loop of Henle?

    <p>NKCC2</p> Signup and view all the answers

    What is the main function of the early distal tubule?

    <p>Reabsorption of ~5% filtered NaCl</p> Signup and view all the answers

    Which cells in the late distal and cortical collecting tubules are responsible for secreting K+?

    <p>Principal cells</p> Signup and view all the answers

    What is the main function of type A intercalated cells in the collecting tubules/ducts?

    <p>Secrete H+ and reabsorb HCO3- in acidosis</p> Signup and view all the answers

    What is the main function of type B intercalated cells in the collecting tubules/ducts?

    <p>Secrete HCO3- and reabsorb H+ in alkalosis</p> Signup and view all the answers

    What is the main function of medullary collecting ducts?

    <p>Control water permeability</p> Signup and view all the answers

    What percentage of filtered Na+ is reabsorbed in the renal tubules?

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

    What is the main function of thick ascending limb of the Loop of Henle?

    <p>Reabsorb Na+, Cl-, K+, HCO3-, Ca++, Mg++</p> Signup and view all the answers

    What is the function of the Na-K ATPase in the basolateral membrane of the proximal tubule cells?

    <p>Transport Na+ out of the cell</p> Signup and view all the answers

    Which transporter facilitates the downhill diffusion of Na+ to drive the reabsorption of K+ in the thick ascending limb of the Loop of Henle?

    <p>NKCC2</p> Signup and view all the answers

    What are the primary active transporters involved in reabsorption from filtrate to interstitium and peritubular capillaries?

    <p>Na$^+$-K$^+$-ATPase and H$^+$-ATPase</p> Signup and view all the answers

    What is the main process coupled to passive water reabsorption?

    <p>Sodium reabsorption</p> Signup and view all the answers

    What limits the amount of material mediated transporters can transport?

    <p>Transport maximum (Tm)</p> Signup and view all the answers

    Where does reabsorption predominately occur?

    <p>Proximal tubule</p> Signup and view all the answers

    What is the site of action of osmotic diuretics?

    <p>Proximal tubule</p> Signup and view all the answers

    Which part of the nephron has urea transporters?

    <p>Inner medullary collecting duct</p> Signup and view all the answers

    What percentage of glucose is reabsorbed in the proximal tubule?

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

    What percentage of sodium is reabsorbed in the proximal tubule?

    <p>5-7%</p> Signup and view all the answers

    What affects water permeability at the proximal tubule and thin descending limb?

    <p>Osmotic diuresis</p> Signup and view all the answers

    What is the primary process that urea reabsorption is dependent on?

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

    What percentage of urea is reabsorbed in the inner medullary collecting duct?

    <p>50%</p> Signup and view all the answers

    What is the primary type of transport involved in sodium reabsorption?

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

    ADH binds to ______ receptors, increases cAMP, and activates protein kinases, inserting AQP2 channels into the luminal membrane

    <p>V2</p> Signup and view all the answers

    Tubules can increase reabsorption rates in response to increased tubular load to maintain Na+ and volume homeostasis in ______ tubules

    <p>distal</p> Signup and view all the answers

    Fractional excretion (FE) expresses solute excretion as a percentage of filtered load and is useful in determining altered tubular transport, not just ______

    <p>GFR</p> Signup and view all the answers

    Rate of urinary excretion of a substance can be affected by glomerular filtration, tubular reabsorption, and tubular ______

    <p>secretion</p> Signup and view all the answers

    Calculating FENA is useful in acute renal failure to determine if it is due to prerenal or ______ pathology

    <p>renal</p> Signup and view all the answers

    Study Notes

    Regulation of Na+ and H2O by ADH and Aldosterone

    • Tubular reabsorption in kidneys is large and highly selective, with 180 L of filtered water per day and high reabsorptive rates for water and ions under physiological control.
    • Reabsorption occurs through diffusion, mediated transport, and bulk flow, with substances moving through transcellular and paracellular routes.
    • Reabsorption from filtrate to interstitium and peritubular capillaries involves passive and active transport, with primary active transporters including Na+-K_-ATPase and H+-ATPase.
    • Sodium reabsorption uses both passive and active transport, with many substances coupled to sodium reabsorption via secondary active transport.
    • Passive water reabsorption by osmosis is coupled mainly to sodium reabsorption, with water permeability varying through different tubules.
    • Transport maximum (Tm) limits the amount of material mediated transporters can transport, leading to conditions like glucosuria in diabetes.
    • Urea reabsorption is dependent on the reabsorption of water and occurs via passive diffusion down its concentration gradient.
    • Reabsorption predominates in the proximal tubule, with variations in Na+ reabsorption and urea reabsorption favoring reabsorption as water is reabsorbed.
    • The proximal tubule is the site of action of osmotic diuretics, causing nonreabsorbed solutes to retain water in the lumen and be excreted.
    • Osmotic diuresis affects water permeability at the proximal tubule and thin descending limb, with examples including mannitol and untreated diabetes mellitus.
    • 65% of glucose and 5–7% of Na+ are reabsorbed in the proximal tubule, while 25% and 2.4% are reabsorbed in the loop of Henle and distal tubule, respectively.
    • The inner medullary collecting duct has urea transporters, with approximately 50% of filtered urea reabsorbed and 50% excreted.

    Regulation of Tubular Reabsorption in the Kidneys

    • Tubules can increase reabsorption rates in response to increased tubular load to maintain Na+ and volume homeostasis in distal tubules
    • Peritubular physical forces: increased arterial pressure raises peritubular capillary pressure; afferent and efferent arterioles reduce peritubular capillary hydrostatic pressure
    • Hormones like aldosterone, angiotensin II, and antidiuretic hormone (ADH) play a crucial role in controlling extracellular fluid (ECF) volume and sodium and water reabsorption
    • Sympathetic nervous system activation decreases Na+ and H2O excretion, increases tubular reabsorption by alpha-adrenergic receptors on tubular epithelium
    • Antidiuretic hormone (ADH) controls ECF osmolarity and is synthesized by the hypothalamus; its secretion is influenced by plasma volume changes
    • ADH binds to V2 receptors, increases cAMP, and activates protein kinases, inserting AQP2 channels into the luminal membrane
    • Rate of urinary excretion of a substance can be affected by glomerular filtration, tubular reabsorption, and tubular secretion
    • Fractional excretion (FE) expresses solute excretion as a percentage of filtered load and is useful in determining altered tubular transport, not just GFR
    • Calculating FENA is useful in acute renal failure to determine if it is due to prerenal or renal pathology
    • For a substance that is freely filtered, renal clearance is equal to GFR
    • Inulin can be used to estimate GFR, while plasma creatinine is a direct index of GFR but overestimates by ~10% and is used to determine the stages of renal failure
    • Clinical case questions related to hypernatremia, renal artery stenosis, potassium secretion, and maximum clearance rate are presented to test understanding of kidney function and regulation.

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    5.5 Renal Tubular Reabsorption and Secretion.pptx

    Description

    Explore the regulation of tubular reabsorption in the kidneys, including the roles of antidiuretic hormone (ADH) and aldosterone, as well as the influence of physical forces and hormones on sodium and water reabsorption. Test your understanding with clinical case questions related to kidney function and regulation.

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