Why, when speaking of the resp sys, are Arteries blue indicating deoxygenated blood and veins red carrying oxygenated blood?
Because Arteries carry blood away fr the heart and in the case of the resp sys away fr the R side of the heart is carrying blood to the lungs to be reoxygenated. Veins carry blood to the heart and in this case O2 rich blood is taken to the L side of the heart to be pumped out to the body.