How does hypoxia differ from hypoxemia?

Hypoxia is a condition characterized by a deficiency in the amount of oxygen reaching the tissues, and it can occur for various reasons. It can be classified into generalized hypoxia, affecting the entire body, and localized hypoxia, which affects only specific tissues or regions. For example, an area of tissue may experience hypoxia due to a blockage in blood flow, even if the overall oxygen levels in the bloodstream are sufficient. This distinction is critical because it emphasizes that hypoxia can arise from factors beyond just blood oxygen levels.

In contrast, hypoxemia specifically refers to low oxygen levels in the blood. It is the measurable condition where the partial pressure of oxygen in the arterial blood is below normal. Hypoxemia can lead to tissue hypoxia, but not all hypoxia is caused by hypoxemia; other causes include carbon monoxide poisoning or anemia, where the blood's ability to carry oxygen is compromised without necessarily involving low oxygen levels in the lungs.

This understanding clarifies why the choice stating that hypoxia includes both generalized and localized deficiencies is valid, as it captures the broader spectrum of oxygen deficiency in tissues, distinguishing it from hypoxemia, which is strictly a blood-related issue.