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Hypoxic pulmonary vasoconstriction
Make it clearer
The lung has a reflex that sounds backwards at first: it closes off vessels exactly where oxygen is missing. And it makes perfect sense.
The lung is full of alveoli, the little sacs where air and blood trade gases. If air is not reaching an alveolus, sending blood there does not accomplish much: there is no oxygen to pick up. So the lung does something smart: the arterioles in that area close down. This is called hypoxic pulmonary vasoconstriction, hypoxic because what triggers it is the lack of oxygen in the alveolus. The blood goes off to the areas that are getting air.
What squeezes the vessel is the smooth muscle in its wall. That muscle has potassium and calcium gates, the voltage-gated channels, which are very sensitive to low oxygen, and they are the ones that order the squeeze.
The problem shows up when the reflex stops being a one-off. If it turns chronic and exaggerated, the whole lung circuit stays squeezed and the pressure inside rises: that is pulmonary hypertension. The right ventricle, which is the one that pushes blood toward the lung, has to pump against that pressure, and in most cases it thickens, which is called hypertrophy.
In brief
Hypoxic pulmonary vasoconstriction is how the lung's arterioles respond to alveolar hypoxia.
When they constrict, they shift blood away from poorly ventilated areas toward those that are getting air.
The lung shuts off the tap where no air is arriving.
The smooth muscle of these arteries has voltage-gated potassium and calcium channels that are sensitive to low oxygen.
If the vasoconstriction becomes chronic and excessive, it can lead to pulmonary hypertension, and in most cases the right ventricle hypertrophies.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Pulmonary Vasoconstriction, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
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