question with heart function

[yoyohomieg5432]

in a situation where the levels of O2 are falling and CO2 is rising, my book says that vasoconstriction occurs, causing an increase in blood pressure. why would you want vasoconstriction? wouldn't this increase resistance and thus less blood would flow? it seems like you'd want vasodilation so you can maximize the blood flow to provide body with more oxygen?

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[HotHamH2O]

in a situation where the levels of O2 are falling and CO2 is rising, my book says that vasoconstriction occurs, causing an increase in blood pressure. why would you want vasoconstriction? wouldn't this increase resistance and thus less blood would flow? it seems like you'd want vasodilation so you can maximize the blood flow to provide body with more oxygen?

Remember that vasoconstriction isn't systemic. In the case of your scenario, the vasoconstriction is pulmonary in order redirect blood flow to the alveoli with a higher O₂ content. It does seem odd because you would think that low oxygen levels should lead to an increased blood flow for an increase in gas exchange. But, the vasoconstriction redistributes the blood to better ventilated areas of the lung and increases total surface area.

Here's a good video on hypoxic pulmonary vasoconstriction
[YOUTUBE]http://www.youtube.com/watch?v=SJ1gu_WRx5o[/YOUTUBE]