Gas exchange: maintaining diffusion gradients
הוצג| English | משמעות |
|---|---|
| ventilation/ˌventɪˈleɪʃn/ | אוורור |
| perfusion/pəˈfjuːʒn/ | הזרמה |
What would explain this observation?
- An exchange surface can be very thin yet fail to deliver enough oxygen when ventilation 通气 or blood flow falls.
Build the model
- Gas exchange occurs by diffusion across a surface.
- Large area, short diffusion distance and maintained concentration gradients support transfer.
- Ventilation refreshes the external medium; perfusion 灌注 carries gases to and from the exchange surface.
- ventilation: Movement of air or water over an exchange surface.
- perfusion: Blood flow through tissue or an exchange surface.
What maintains an oxygen gradient across the lung exchange surface?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
Ventilation refreshes alveolar air and blood flow carries oxygen away, so both sides of the surface keep the partial-pressure gradient steep. Stopping blood flow would let equilibration flatten it, and a longer path would slow diffusion.
Match each technical term to its precise meaning.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Distinguish movement of the whole medium from diffusion across the membrane.
- Ventilation and perfusion work together, while haemoglobin helps transport oxygen in blood.
- A change in breathing rate alone does not measure oxygen uptake.
In the lab: Use an approved model or published respiratory data. Compare exchange surface area, diffusion path and flow. For human demonstrations use voluntary resting measurements; do not induce breathlessness or hyperventilation.
Which two habits make the investigation or model in this case more defensible?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: tidal volume is 0.50 L and breathing rate is 12 breaths/min.
- Minute ventilation = 0.50 × 12 = 6.0 L/min.
- This includes dead-space ventilation and is not identical to alveolar ventilation.
Your turn: Tidal volume is 0.60 L and breathing rate is 10 breaths/min. Find minute ventilation.
Tidal volume is 0.60 L and breathing rate is 10 breaths/min. Find minute ventilation.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
The result is 6 L/min. Known: tidal volume 0.60 L; breathing rate 10 breaths per minute. Use minute ventilation = tidal volume x rate. Ventilation = 0.60 x 10 = 6 litres per minute. Alveolar ventilation is lower once dead space is subtracted.
Check the conclusion and its limits
- Air entering the lungs is not all exchanged with blood.
- Oxygen and carbon dioxide diffuse in opposite net directions because their own gradients differ.
Not true: Minute ventilation directly equals oxygen uptake. Ventilation moves air into the lungs; oxygen uptake is what crosses into the blood. Dead-space air never reaches the exchange surface, and uptake depends on diffusion and blood flow, so the two quantities differ.
- Gas exchange occurs by diffusion across a surface.
- Distinguish movement of the whole medium from diffusion across the membrane.
- Watch for: air entering the lungs is not all exchanged with blood.
Write from a minute ventilation of 12 litres per minute
- Tidal volume is 0.80 L and the breathing rate is 15 breaths per minute.
- Find minute ventilation. It includes dead space.
Ventilation moves air into the lungs; oxygen uptake is what crosses into the blood.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
True. Ventilation moves air into the lungs; oxygen uptake is what crosses into the blood. Dead-space air never reaches the exchange surface, and uptake depends on diffusion and blood flow, so the two quantities differ.
Movement of air or water over an exchange surface: write the technical term.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
ventilation means Movement of air or water over an exchange surface.
Tidal volume is 0.80 L and breathing rate is 15 breaths per minute. What is the minute ventilation, and why is it not the same as alveolar ventilation?
0.80 times 15 is 12. Dead-space air is moved but does not all meet the exchange surface.
What is the minute ventilation?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
0.80 times 15 is 12 litres per minute, and dead space is still included.