Final answer:
Red blood cells are produced in the bone marrow and have a lifespan of around 120 days, after which they are broken down by macrophages.
Step-by-step explanation:
Red blood cells (RBC), also known as erythrocytes, are formed in the red marrow of bones such as the long bones, rib bones, skull, and vertebrae. In adults, the formation of RBCs is primarily restricted to the pelvis, cranium, vertebrae, sternum, and the ends of the long bones like the femur and humerus. The production of RBCs, also referred to as hemopoiesis or hematopoiesis, is a continuous process as the red blood cells have a lifespan of only about 120 days, or approximately four months. Once they have reached the end of their lifespan, erythrocytes are destroyed by macrophages primarily located within the bone marrow, liver, and spleen.