Final answer:
Erythrocytes circulate for approximately 120 days before being removed from the bloodstream by macrophages in the bone marrow, liver, and spleen. The hemoglobin from the degraded erythrocytes undergoes further processing called cleavage of the methane bridge.
Step-by-step explanation:
Erythrocytes, or red blood cells, have an average lifespan of 120 days in the circulation. After this time, they are removed from the bloodstream by macrophages located in the bone marrow, liver, and spleen. The hemoglobin from the degraded erythrocytes is further processed through cleavage of the methane bridge to form choleglobin, an iron pyrrole complex. This process occurs primarily in the spleen, liver, and bone marrow.