What is stimulated in tissues when the concentration of oxygen decreases?

When the concentration of oxygen decreases in tissues, the body responds by promoting the release of oxygen from hemoglobin. This process is governed by the oxygen-hemoglobin dissociation curve, which illustrates how hemoglobin's affinity for oxygen changes with varying levels of oxygen saturation and other factors such as pH and carbon dioxide levels.

In hypoxic conditions, where oxygen concentration is low, hemoglobin tends to release its bound oxygen more readily to meet the metabolic demands of tissues. The presence of elevated carbon dioxide and protons (lower pH) in the tissues further facilitates this release, enhancing oxygen delivery where it is most needed.

This reaction is critical in ensuring that oxygen is supplied to cells for aerobic metabolism, especially when they require more energy due to increased activity or other physiological demands. By understanding this key physiological response, it becomes clear why the correct answer revolves around the concept of hemoglobin releasing oxygen when faced with decreased oxygen availability.