Erythrocytes, or red blood cells (RBCs), are primarily responsible for carrying oxygen from the lungs to the body's tissues and transporting carbon dioxide from the tissues back to the lungs for expulsion. Hemoglobin, a protein within RBCs, facilitates oxygen binding. Carbon dioxide is transported through multiple mechanisms, including binding to hemoglobin or dissolving in plasma. Consequently, the principal role of red blood cells is the conveyance of oxygen and carbon dioxide.