Blood group antigens are carbohydrates that are attached to proteins or lipids. An antigen is a substance foreign to the body that causes an immune response. An immune response occurs when antibodies, which are proteins in your immune system, are summoned to attack an antigen.
Blood that reaches the lungs travels throughout a network of small blood vessels, where oxygen moves into the blood and carbon dioxide moves out of the blood, according to the National Heart, Lung and Blood Institute.
The lungs are two organs that pass oxygen into every red blood cell carried through their capillaries; a major organ of the respiratory system, where the exchange of oxygen and carbon dioxide in the bloodstream takes place; expands to suck in air and shrinks to squeeze air out.