As well as specific receptors for iron, transferrin has specific receptors for sites on the developing normoblast and RE cell. Once bound to the cell membrane, the transferrin changes shape and releases the iron. It then returns to the portal circulation to bind more iron. The iron is moved into the developing red cell by a process similar to pinocytosis called ropheocytosis. Iron storage Iron is stored as either ferritin or hemosiderin.
Ferritin is water soluble and a very small amount is dissolved in the plasma.
The more ferritin stored the more dissolved in the plasma. Ferritin is not visible by light microscopy, nor is it stained by the Prussian Blue reaction. It is preferentially used before hemosiderin, probably because it is soluble. The protein shell has been altered and as a result it is water insoluble. It can be seen by light microscopy as gold-brown granules and is demonstrated by the Prussian Blue stain.