Hemoglobin A is the most common type of hemoglobin found in healthy adults. It is a protein in red blood cells that carries oxygen from the lungs to the rest of the body and helps transport carbon dioxide back to the lungs for exhalation. Hemoglobin A consists of two alpha and two beta chains, which work together to bind oxygen efficiently. In individuals with certain medical conditions, such as sickle cell disease or thalassemia, the structure of hemoglobin can be altered, leading to different types like hemoglobin S or hemoglobin E. These variations can affect the ability of red blood cells to function properly, impacting overall health and oxygen delivery.