Iron moves primarily by being bound to the protein transferrin in the bloodstream. Greater than 95% of iron in plasma is attached to transferrin, which acts as its circulating transport. Transferrin then delivers the iron to various cells, especially erythrocyte precursors (erythroid progenitor cells) in the bone marrow, where it is used to produce red blood cells (RBCs).
Here's a more detailed breakdown:
- Absorption: Iron is absorbed from the diet in the small intestine.
- Entry into Circulation: Once absorbed, iron enters the bloodstream.
- Binding to Transferrin: In the plasma, iron (specifically ferric iron, Fe3+) binds to transferrin. Each transferrin molecule can bind two iron atoms.
- Transportation: Transferrin carries iron throughout the body.
- Delivery to Cells: Transferrin delivers iron to cells that have transferrin receptors on their surface. The transferrin-iron complex binds to these receptors.
- Cellular Uptake: The complex is then internalized into the cell via endocytosis.
- Iron Release: Within the cell, iron is released from transferrin.
- Utilization or Storage: The iron is then used for various cellular processes (e.g., hemoglobin synthesis in red blood cell precursors) or stored as ferritin or hemosiderin.
In essence, transferrin acts as the dedicated iron delivery service within the body, ensuring that iron is transported safely and efficiently to where it's needed.
