Iron Metabolism Quiz

See Iron storage and recycling. Option D identifies the main reserve storage compartments: liver cells and tissue macrophages. Hepatocytes, the main functional cells of the liver, store iron alongside macrophages in the liver, spleen and marrow. Macrophages recover iron when they engulf old red cells and either retain it or return it to the circulation. Ferritin keeps iron safely enclosed in a protein shell, while haemosiderin is a less readily mobilised aggregated storage form. Most total body iron is already in haemoglobin, but functional haemoglobin iron is distinct from the reserve stores asked about here.

Free plasma iron (C) is not a normal reserve because it can promote tissue-damaging reactions; circulating iron is mainly carried by transferrin. A confuses temporary retention in intestinal lining cells with permanent storage, since these cells are regularly shed. B describes myoglobin, which binds oxygen in muscle rather than providing the main reserve from which new red cells obtain iron. Renal tubular cells in E do not form an iron-excretion store; iron balance is controlled mainly through absorption, without a regulated pathway for actively eliminating excess.