- This response is the opposite of that in other organs, where hypoxia causes vasodilation.
- Physiologically, this effect is important because local vasoconstriction diverts blood away from poorly ventilated, hypoxic regions of the lung and toward well-ventilated regions.
- Fetal pulmonary vascular resistance is very high because of generalized hypoxic vasoconstriction; as a result, blood flow through the fetal lungs is low. With the first breath, the alveoli of the neonate are oxygenated, pulmonary vascular resistance decreases, and pulmonary blood flow increases and becomes equal to cardiac output (as occurs in the adult).
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