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.
Blood under lower pressure moves more slowly. Slower moving blood has more time to exchange carbon dioxide for oxygen while passing through the lungs. The same is true when bl â¦ ood is passing through capillaries.