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.
Let's review. Your blood travels to the lungs to pick up oxygen. It's propelled toward your lungs by the pumping action of the right ventricle of the heart. When the ventricle contracts, blood is pushed into the short pulmonary trunk before branching toward each lung through the right and left pulmonary arteries.