What adaptation occurs in response to increased altitude over time?

When an individual is exposed to increased altitude over time, the body undergoes several physiological adaptations to cope with reduced oxygen levels. One of the key adaptations is the increase in capillary density.

At higher altitudes, the availability of oxygen decreases, which can lead to hypoxia (a deficiency in the amount of oxygen reaching the tissues). To counteract this, the body enhances its ability to transport and utilize oxygen. Increasing capillary density improves oxygen delivery to muscles and other tissues, allowing for better oxygen exchange and utilization. This adaptation supports overall performance and endurance as the body adjusts to the lower oxygen environment.

As for other options, decreased lung capacity does not occur; rather, lung function can adapt positively by optimizing gas exchange. Increased breathing frequency may happen initially in response to altitude, but it should normalize as the body acclimatizes. Decreased heart size is not a typical adaptation to high altitude; instead, the heart may actually increase in size or efficiency to meet the body's increased demand for oxygen. Thus, increased capillary density stands out as the significant and beneficial response to prolonged exposure to higher altitudes.