Red blood cells (erythrocytes) transport oxygen and carbon dioxide throughout the body. Hemoglobin in red blood cells binds oxygen in the lungs and releases it in tissues. Factors like pH, carbon dioxide levels, and 2,3-BPG affect hemoglobin's affinity for oxygen. Sickle cell anemia and thalassemias are genetic disorders affecting hemoglobin and red blood cells. Bilirubin is produced from hemoglobin breakdown; jaundice occurs when bilirubin levels are elevated due to issues with production, conjugation, or excretion of bilirubin.