Which mechanism underlies acclimatisation to chronic high altitude?

1. Acclimatisation is the adjustment the respiratory system makes to chronic high altitude exposure. 2. The low partial pressure of oxygen leaves haemoglobin poorly saturated and tissue oxygen low. 3. Low tissue oxygen stimulates the kidneys to produce erythropoietin. 4. Erythropoietin stimulates the production of erythrocytes, so more circulate over time. 5. More red cells mean more haemoglobin, so more oxygen is carried even though each molecule is less saturated. 6. Neither lung volume nor alveolar thickness changes with altitude, so the first and third options describe adaptations that do not occur. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 22 "The Respiratory System", section 22.6 Modifications in Respiratory Functions_