Examination of mountain climbers who have spent a long time in a high-altitude region revealed increase of erythrocyte number (over 6 × 1012/l) and haemoglobin concentration (over 170 g/l). What mechanism caused this phenomenon?

Answer options

1. Improved ability of tissue for oxygen utilization
2. Intensified processes of anoxic energy production
3. Weakening of intracellular erythrocyte haemolysis
4. Weakening of erythrocyte haemolysis in bloodstream
5. Intensified production of erythropoietin by the kidneys