Loading…
Especially relevant to University of Oxford and University of Cambridge.
Say your answer out loud first, then jot down the key points you made. Writing it helps you spot gaps — and it's what the AI feedback reads.
0 words
Applying gas exchange, partial pressures and homeostatic control to an unfamiliar scenario.
A structure to build your own answer on — not a script.
Clarify the physics
Oxygen fraction (~21%) is unchanged; total atmospheric pressure falls, so the partial pressure of oxygen falls.
Gas exchange
Lower partial pressure gradient → less oxygen diffuses into blood → lower haemoglobin saturation → hypoxaemia.
Immediate response
Peripheral chemoreceptors detect low oxygen → increased ventilation and heart rate → feeling breathless.
Consequence
Hyperventilation blows off CO2 → respiratory alkalosis, which limits the drive to breathe.
Acclimatisation
Kidneys excrete bicarbonate; erythropoietin → more red blood cells over weeks; other changes at cellular level.
A strong but not perfect answer. Read the notes to see why it works — then make your own version with your experiences.
The first thing I'd clarify is that the air at the top of a mountain still contains about 21% oxygen1. The difference is that atmospheric pressure is much lower, so the partial pressure of oxygen — effectively how hard oxygen is being 'pushed' into the lungs — is lower.
That matters because oxygen moves from the alveoli into the blood by diffusion, down a partial pressure gradient. With a smaller gradient, less oxygen enters the blood, haemoglobin is less saturated, and tissues receive less oxygen.
The body detects this through chemoreceptors — I think mainly the ones in the carotid arteries2 — which sense low oxygen and increase the rate and depth of breathing. The heart rate also rises. That's why people feel breathless: their body is trying to compensate.
But breathing faster also blows off more carbon dioxide, which makes the blood more alkaline. Since CO2 is normally a strong stimulus to breathe, losing it limits how much further breathing can increase — so there's a tension between the two3.
If someone stays at altitude, over days the kidneys excrete more bicarbonate to correct the alkalosis, allowing breathing to increase further. Over weeks, the kidneys release more erythropoietin, which stimulates red blood cell production, so the blood can carry more oxygen. I believe there are also changes in how readily haemoglobin releases oxygen to the tissues.
That's why athletes train at altitude — to increase their red cell mass — though I'd guess the benefit depends4
Real interviews are won and lost here. Answer each one aloud.