C. Systemic arterioles respond to a decrease in PO₂ by dilating, but pulmonary arterioles constrict in response to decreased PO₂.
Explanation:
In the arterioles, vasoconstriction is a response to high oxygen while vasodilation is a response to carbon dioxide and low pH. However, in the pulmonary arterioles, vasoconstriction occurs as a response to low oxygen and this mechanism is called hypoxic pulmonary vasoconstriction (HPV).
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