Red blood cells, also known as erythrocytes, are an essential component of blood that carry oxygen from the lungs to the rest of the body and transport carbon dioxide back to the lungs to be exhaled. They are produced in the bone marrow and typically live for about 120 days before being removed from circulation by macrophages in the spleen and liver. The main function of red blood cells is to deliver oxygen to the bodys tissues, where it is used to produce energy. Red blood cells contain a protein called hemoglobin, which allows them to carry oxygen. Certain conditions within the body, such as a lack of oxygen or blood cells, can trigger the production of more red blood cells. Red blood cell donations are important to help patients who cannot produce enough red blood cells. Foods rich in iron, vitamins B-2, B-12, and B-3, and folate are needed to build healthy red blood cells.