po2 and pco2 effects on pulm and systemic circulation

[tarsuc]

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Po2 and Pco2
exert opposite effects on pulmonary and systemic circulation. pg613 fa.
can someone explain?

but pco2 effects in pulm and systemic arent opposite ?

 

[gettheleadout]

They must mean O2 and CO2 generate opposite effects relative to each other in both circulatory segments. Systemically, high PCO2 stimulates hypercapnic ventilatory drive, whereas (e.g. in the case of chronic pulmonary disease) low PO2 induces hypoxic ventilatory drive. In the pulmonary circulation, low PO2 stimulates hypoxic vasoconstriction, whereas high PCO2 also stimulates vasoconstriction (via low pH).

 

[tarsuc]

oh okay . got it now. thankss.

High pco2 causes vasoconstriction by action at the level of the central and peripheral chemoreceptors? (leading to inc symp)

Also do you the mechanism of hypoxic vasoconstriction in the lung? how does that occur?

 

[gettheleadout]

oh okay . got it now. thankss.

High pco2 causes vasoconstriction by action at the level of the central and peripheral chemoreceptors? (leading to inc symp)

Also do you the mechanism of hypoxic vasoconstriction in the lung? how does that occur?

Yeah, at low arterial pressures the high PCO2 sensed by the carotid and aortic chemoreceptors does effect sympathetic vasoconstriction to increase arterial pressure. As far as I know, the exact mechanism for hypoxic vasoconstriction isn't known, but it's presumed to be a direct effect of oxygen on the smooth muscle cells of the pulmonary vasculature.