User:LambGirlToTheSlaughter/Blue blood (nobles)

Sangre azul or blue blood is a term used internationally, especially in the West, to refer to people descended from or belonging to noble families, either royal or aristocratic.

This term was originally used to refer to clarity of the skin color of “los privilegiados,” who didn’t do physical labor or suffer inclement weather, while the peasants and craftsmen, with long working days, had darker skin. Veins seen through pale skin have a bluish tint. Ladies were very careful not to be exposed too much to the sun. The more pale and thin the skin was, the more attractive it was for the gentlemen who could make out the bluish veins in the beautiful feminine busts, reminding them of precious and delicate marble. The archetype of “el príncipe azul” or the blue prince, often present in children's stories, seems to have the same origin. Royal people whose blood was type O were called “de sangre azul” or blue blooded because they could donate to all of the other blood types, but could only receive their own blood type. Anyone could receive royal blood, but not everyone could give blood to the royals.

In biology, the usual diagram of the circulatory system has the color red in the arteries and the color blue in the veins, by analogy with hemoglobin, red pigment for the iron responsible for the transport of oxygen. In some animal species, the pigment for the blood in hemolymph (a circulatory liquid equivalent to the blood in mollusks and arthropods) contains hemocyanin that instead of iron, contains copper; it is found in most mollusks and some arthropods, and is dark blue.