Érythrocytes, commonly known as red blood cells, are the most abundant type of cells in the blood. Their primary function is to transport oxygen from the lungs to the body's tissues and return carbon dioxide from the tissues back to the lungs. They contain a protein called hemoglobin, which binds to oxygen and gives these cells their red color. These cells are produced in the bone marrow and have a lifespan of about 120 days. Once they age or become damaged, they are removed from circulation by the spleen and liver. Maintaining a healthy level of érythrocytes is essential for overall health and proper bodily function.