Which of the following best describes "hypoxia"?

Hypoxia refers specifically to a condition in which there is insufficient oxygen reaching the tissues of the body. This can occur at high altitudes where the partial pressure of oxygen is lower, making it more difficult for oxygen to enter the bloodstream. As a result, the organs and tissues do not receive the amount of oxygen they need to function properly, which can lead to symptoms such as fatigue, confusion, and even loss of consciousness if not addressed.

Understanding hypoxia is crucial for flight attendants, as they need to be aware of the potential for this condition at high altitudes and be able to recognize the signs and symptoms in themselves and passengers. The other options pertain to related aspects of altitude but do not accurately describe hypoxia itself. Excessive oxygen levels in the blood is not a typical concern in aviation settings at altitude. Increased heart rate may occur as a physiological response to lower oxygen levels but is not hypoxia itself. Dehydration can be an issue at high altitudes but does not directly relate to the lack of oxygen in tissues. Thus, insufficient oxygen reaching the tissues is the clearest and most appropriate description of hypoxia.