RBC or Red blood cells are the most common type of blood cell (other then WBC and platelets) and the vertebrate organism's principal means of delivering oxygen (O2) to the body tissues—via blood flow through the circulatory system. RBCs take up oxygen in the lungs or gills and release it into tissues while squeezing through the body's capillaries.
Human erythrocytes are produced through a process named erythropoiesis, developing from committed stem cells/Bone Marrow to mature erythrocytes in about 7 days [Through the Erythropoiesis process erythrocytes are continuously produced in the red bone marrow of large bones, at a rate of about 2 million per second in a healthy adult. Just before and after leaving the bone marrow, the developing cells are known as reticulocytes; these comprise about 1% of circulating red blood cells]. When matured, in a healthy individual these cells live in blood circulation for about 100 to 120 days (and 80 to 90 days in a full term infant).