SDN Members don't see this ad. (About Ads) I was curious. I realize that if alveoli are poorly ventilated (low O2 and high CO2), arterioles constrict to shunt blood to better oxygenated areas and that high O2 and low CO2 in alveoli cause dilation of arterioles to allow for greater blood flow. I was curious about what signals cause bronchioles to dilate and constrict. For example, if tissues are highly metabolic and venous blood vessels are delivering more CO2 back to the alveoli, do bronchioles dilate to allow greater diffusion of CO2 out of the lungs? (thus, a signal such as epinephrine might trigger such effect on the bronchioles)...would this be correct? What other oxygen/CO2 conditions trigger constriction/dilation of bronchioles? Thanks.