PATHOLOGY

Detailed explanation-1: -Blood is always red. Blood that has been oxygenated (mostly flowing through the arteries) is bright red and blood that has lost its oxygen (mostly flowing through the veins) is dark red. Anyone who has donated blood or had their blood drawn by a nurse can attest that deoxygenated blood is dark red and not blue.

Detailed explanation-2: -Veins, such as the ones on the back of your hands, are closer to your skin surface than your arteries, which makes it possible to see them. Venous blood appears blue through lighter skin because of a trick that light plays on us. Through light skin, some veins look blue.

Detailed explanation-3: -“Blood is not blue.” Well, at least in humans. Blue blood does flow through the veins of a few living things, including horseshoe crabs and octopuses. (The blood in those animals uses a copper-containing protein called hemocyanin to carry oxygen, which explains the blue color.)