The oxygen molecule from the atmosphere enters due to inhalation. Most of these molecules are bonded to the hemoglobin protein and are delivered to the blood through an exchange system. Some of these compounds disintegrate in the bloodstream's plasma. The release of bound oxygen to maintain dissolved oxygen levels results from the decrease in dissolved oxygen in the plasma.
Hemoglobin's affinity for oxygen reduces as blood plasma's pH drops (or turns more acidic). This is because H+ ions bind to hemoglobin amino acids more frequently as blood plasma gets more acidic. The Bohr effect is a name for this. As plasma pH rises (=becomes more basic; alkaline), the situation changes.
