What happens to arterioles in the setting of low PO2?

• A. They dilate to increase blood flow
• B. They constrict to shunt blood away from damaged areas
• C. They remain unchanged regardless of PO2 levels
• D. They enlarge to decrease vascular resistance

Answer: (B)

In the setting of low partial oxygen pressure (low PO2), arterioles constrict in a process known as hypoxic vasoconstriction. This physiological response is critical because it helps redirect blood flow away from poorly ventilated or damaged areas of the lung to regions that are better oxygenated. The goal of this mechanism is to optimize gas exchange and improve overall oxygen delivery to the tissues in the body, effectively prioritizing well-ventilated regions.

When oxygen levels are low, the body reacts by constricting the small blood vessels (arterioles) in the affected area. This reduces blood flow to those regions, minimizing the proportion of blood that is circulating through areas where oxygen cannot be adequately absorbed, thus enhancing the efficiency of pulmonary gas exchange in parts of the lung that still receive sufficient oxygen. This response is crucial during conditions such as respiratory distress or chronic lung diseases where some parts of the lung may experience lower oxygen levels.

The choices regarding dilation or unchanged states do not accurately reflect the body's adaptive mechanisms to low PO2 levels, while the idea of enlargement to decrease vascular resistance doesn't align with the physiological response to hypoxia. Therefore, arteriolar constriction in response to low oxygen is a well-established physiological principle that serves a