Ultrafiltration and Selective Reabsorption in the Nephron · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.
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How the nephron filters then reclaims

Science · The Human Body · ages 17-18
Name ______________________   Date ____________

  1. Which substance is largely retained by a healthy glomerular filtration barrier?

    • Dissolved urea
    • Dissolved glucose molecules
    • Most large plasma proteins

  2. What helps maintain high pressure in glomerular capillaries?

    • Arterial pressure and resistance to blood leaving
    • Active pumping of filtrate by cells lining the capsule
    • Contraction of the proximal tubule around the glomerulus

  3. Where and how does reabsorption of filtered glucose begin?

    • In the collecting duct by osmosis
    • In the glomerulus through its filtration slits
    • In the proximal tubule by co-transport

  4. At normal blood glucose levels, why does a routine urine glucose test usually give a negative result?

    • The filter blocks glucose before it reaches the tubule
    • The proximal tubule reabsorbs almost all filtered glucose
    • The capsule breaks down glucose before it can enter the proximal tubule

  5. Which comparison describes glomerular filtration and glucose entry into proximal tubule cells?

    • Filtration uses pressure; glucose entry uses sodium co-transport
    • Filtration uses carriers; glucose entry uses osmosis
    • Filtration uses sodium co-transport; glucose entry uses ATP-driven glucose pumps

  6. What directly drives glucose entry through a sodium-glucose co-transporter in a proximal tubule cell?

    • Blood pressure forcing glucose through the co-transporter
    • ATP breakdown by the sodium-glucose co-transporter itself
    • Sodium moving down its electrochemical gradient

  7. If filtered glucose arrives faster than the tubule's maximum reabsorption rate, some remains in the fluid that becomes urine.

    Circle one:   True   False

  8. A urine test detects glucose. Someone says this proves diabetes. Which response fits?

    • The result has more than one possible cause and cannot confirm diabetes alone
    • The result confirms diabetes without further blood measurements
    • The result rules out diabetes because glucose cannot pass the glomerular filter
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Answer key

For grown-ups. Fold this page away before handing over the rest.

How the nephron filters then reclaims W1-mt_vSKfoJN6zh-s1

  1. Most large plasma proteins · The healthy barrier retains most large plasma proteins. Urea and glucose enter the filtrate readily.
  2. Arterial pressure and resistance to blood leaving · Arterial blood supplies pressure, and resistance to outflow helps maintain glomerular pressure. Both arterioles affect this pressure.
  3. In the proximal tubule by co-transport · Sodium-glucose co-transport brings glucose from filtrate into proximal tubule cells. Glucose then leaves those cells towards blood.
  4. The proximal tubule reabsorbs almost all filtered glucose · The proximal tubule normally recovers almost all filtered glucose. The tiny amount reaching urine is usually below routine detection.
  5. Filtration uses pressure; glucose entry uses sodium co-transport · Net pressure drives glomerular filtration. Sodium-glucose co-transport brings glucose from filtrate into proximal tubule cells.
  6. Sodium moving down its electrochemical gradient · Sodium's movement down its electrochemical gradient drives coupled glucose entry. A separate pump uses ATP to maintain that gradient.
  7. True · Transport has a maximum rate. Glucose arriving above that rate cannot all be recovered, so some remains in the fluid that becomes urine.
  8. The result has more than one possible cause and cannot confirm diabetes alone · Diabetes can raise the filtered glucose load beyond transport capacity. Reduced tubular glucose transport can also cause urinary glucose, so this result alone is not diagnostic.
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