Erythrocyte damage such as osmotic shock, oxidative stress, or energy depletion promotes the generation of prostaglandin E2 by activating cyclooxygenase, which triggers a permeable Ca+2 cation channel. Ca+2 further promotes the transfer of Phosphatidylserine from the cell membrane inside to the outer by a scramblase. Macrophages recognize phosphatidylserine at the surface of the erythrocyte which engulfs and degrade the affected cells. Also, the revealing phosphatidylserine red cell may bind to the vascular wall, interfering with microvessels. Erythrocyte shrinkage and exposure to phosphatidylserine ("eryptosis") mimic apoptosis characteristics in nucleated cells which, however, involve many processes lacking in red cells. Several conditions cause premature eryptosis, thereby favoring anemia progress. Moreover, eryptosis may be a faulty mechanism for erythrocytes to avoid hemolysis. Phosphatidylserine has been considered the key marker of eryptosis and serves as the primary booster in the reticuloendothelial system to eliminate red blood cells by the macrophage.