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 carries oxygen to the cells throughout the entire body, and clears the carbon dioxide from the cells to be expelled by the body via the lungs. If it didn't travel â¦ around the body, it wouldn't be able to move anything and the cells would not get the things they require and thus would die.