Tissue Fluid and Its Return to the Circulation · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.
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How tissue fluid leaves and returns

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

  1. Which group is mainly retained by an ordinary tissue capillary wall?

    • Most large plasma proteins
    • Dissolved glucose
    • Water and small sodium ions

  2. Which pressure favours movement of fluid out of a tissue capillary?

    • Plasma protein osmotic pressure
    • Hydrostatic pressure of capillary blood
    • Osmotic pressure inside circulating red blood cells

  3. A simplified model has hydrostatic pressure of 32 mmHg at the arterial end and 14 mmHg at the venous end. Opposing osmotic pressure is 22 mmHg at both ends. Where does it predict outward filtration?

    • Only at the venous end
    • Equally at both vessel ends
    • At the arterial end

  4. Plasma protein concentration falls. How can this contribute to oedema?

    • It raises hydrostatic pressure throughout the capillary
    • It weakens osmotic opposition to filtration
    • It reduces water permeability throughout the capillary

  5. In many tissues at steady state, which route returns net filtered tissue fluid to blood?

    • Through lymph vessels into venous blood
    • Through pores in red blood cells
    • Through the interior of neighbouring tissue cells

  6. Capillary hydrostatic pressure rises while other exchange conditions stay unchanged. What can happen?

    • Less filtration and tissue fluid
    • No filtration across the capillary wall
    • More filtration and possible oedema

  7. A hypothetical fluid-balance model filters 20 litres in one day. Of this, 17 litres return directly. No fluid accumulates and the rest returns through lymph. How many litres return through lymph?

    Answer: ______________

  8. A student says hydrostatic pressure rises along a capillary and drives inward flow. In a simplified model it falls from 36 to 18 mmHg, while opposing osmotic pressure stays at 25 mmHg. Which correction fits?

    • Pressure falls; the venous-end osmotic effect exceeds hydrostatic pressure
    • Pressure rises; hydrostatic pressure then pulls water into the blood
    • Pressure stays unchanged; the venous-end protein concentration falls to zero
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Answer key

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How tissue fluid leaves and returns W1-mt_0jw7uXpK3C-s1

  1. Most large plasma proteins · Ordinary tissue capillaries restrict most large plasma proteins. Water and small dissolved substances can cross.
  2. Hydrostatic pressure of capillary blood · Capillary hydrostatic pressure favours outward filtration. The osmotic effect of retained plasma proteins opposes it.
  3. At the arterial end · At the arterial end, 32 exceeds 22 mmHg, predicting outward flow. At the venous end, 14 is below 22 mmHg.
  4. It weakens osmotic opposition to filtration · Less plasma protein weakens osmotic opposition to filtration. Fluid may accumulate if lymph drainage cannot remove the additional net filtered fluid.
  5. Through lymph vessels into venous blood · Lymph vessels return net filtered tissue fluid to blood. Continuous venous-end reabsorption is not universal.
  6. More filtration and possible oedema · Higher capillary hydrostatic pressure favours more filtration. Oedema is possible if lymph drainage cannot remove the additional fluid.
  7. 3 · Lymph return in the stated model is 20 - 17 = 3 litres. These are hypothetical values, not universal daily measurements.
  8. Pressure falls; the venous-end osmotic effect exceeds hydrostatic pressure · Hydrostatic pressure falls in the stated model. At the venous end, 18 is below the opposing 25 mmHg, predicting inward flow.
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