Final answer:
At oxygen concentrations of 12-14%, the body enters a state of mild hypoxia, prompting increased oxygen pick-up by hemoglobin in red blood cells and potential stimulation of erythropoietin to raise red blood cell production to cope with lower oxygen availability.
Step-by-step explanation:
When the body experiences O₂ concentrations of 12-14%, it is typically considered a state of mild hypoxia. At these oxygen levels, the circulation picks up oxygen for cellular use more aggressively and tries to drop off carbon dioxide for removal from the body. Our red blood cells, which contain hemoglobin, tremendously amplify the capacity of our blood to carry oxygen. Although the concentration of dissolved O₂ in blood serum at body temperature is low, hemoglobin increases the overall oxygen capacity.
However, if concentration levels of O₂ were to drop in the environment or due to a medical condition, the body would respond by producing more erythrocytes (red blood cells) via the stimulation of erythropoietin (EPO), enhancing oxygen transport capacity and coping with the lower oxygen availability.
Mechanisms like the oxygen-hemoglobin saturation/dissociation curve help regulate the delivery of oxygen to varying tissues, which can have different metabolic rates. Therefore, even at lower environmental O₂ concentrations, our bodies have adaptive measures to ensure that tissues receive sufficient oxygen to maintain energy homeostasis. However, sustained low oxygen environments, such as high altitudes, may require additional acclimatization, such as increasing red blood cell count over time, to cope with the reduced oxygen availability.