Final answer:
In the human body, red blood cells are replaced every four months. Bone remodeling is a continuous process, and the head of the femur may be completely replaced every six months. The process of replacing blood elements, including red blood cells and bone mass, is called hemopoiesis or hematopoiesis.
Step-by-step explanation:
In the human body, red blood cells are replaced approximately every four months. These cells are made in the red marrow of bones, with each red blood cell having a lifespan of about 120 days. After their lifespan is completed, they are broken down in the liver and spleen. Minerals such as iron extracted from the hemoglobin molecules in red blood cells are recycled in the bone marrow and used to produce new hemoglobin for new red blood cells.
Bone remodeling is also a continuous process, with a percentage of bone mass being recycled every week. Specifically, the head of the femur may be completely replaced about every six months, while other areas like the shaft of the bone change more slowly. The process of creating new blood elements, called hemopoiesis or hematopoiesis, is crucial for replacing the formed elements of blood that live only a short time.