(1) The circulating fluid (plasma) and suspended formed elements, such as red blood cells, white blood cells and platelets in the vascular system of humans and other vertebrates.
(2) A functionally similar fluid flowing in the bodies of many animals (e.g. hemolymph in insects).
In humans and other vertebrates, the blood is pumped through the body by the heart, and appears bright-red when hemoglobin is oxygenated. Its major functions include the following:
Word origin: Old English blōd, Proto-Germanic *blodam, of uncertain origin.