L11: Absorption Of Iron And Gastrointestinal Disease Flashcards
Why is iron important
Oxygen transport
Electron transport by cytochromes
Regulation of enzymes
Cell cycle control
Can iron be actively excreted
No so the process of iron has to be tightly regulated for balance
What happens when erythrocytes become old
Engulfed by macrophages
Haem is Brocken to biliverdin then to bilirubin to produce bile
What is the major organ for iron storage
Liver
How can iron be lost in females
Menstruation (periods)
What are dietary iron
Inorganic
Haem
What form is iron in within inorganic
Ferric (fe3+)
Is ferric iron absorbed well
No because it has to be reduces to ferrous iron (fe2+)
Is haem absorbed well
Yes
Where is most of the iron absorbed in the body
Duodenum
How is iron absorbed in enterocytes
1) fe3+ is reduced to fe2+ by Dcytb enzyme and acid in the stomach
2) fe2+ is absorbed by DMT1
3) in the cell fe2+ is used in the cell or stored in the cell by binding to ferritin so iron does not drive free radicals (gives damage)
4) or fe2+ can be effluxed out of the enterocyte into the blood
5) FPN effluxes fe2+ out
6) fe2+ is oxidised to fe3+ to hephaestin
7) fe3 becomes bound to transferrin so iron is inert
How is circulating iron absorbed in a non-enterocyte cell
1) transferrin bound iron is taken in by a transferrin receptor
2) cells express transferrin receptor on the cell surface to take in iron
How is haem iron absorbed into enterocytes
1) HCP1 takes in haem iron into the cell
2) haem iron is then Brocken down by HO-1 enzyme to release biliverdin and free iron (can become bound to ferritin or used)
What happens when HO-1 releases biliverdin from haem iron
Biliverdin is catalysed by biliverdin reductase to give bilirubin
What does build up of bilirubin give
Jaundice
Which major hormone regulates iron levels
Hepcidin
Which organ is hepcidin produced in
Liver
What is the action of hepcidin
Inhibit iron absorption
How does hepcidin inhibit iron absorption
Hepcidin binds on the iron efflux transporter Fpn to block iron efflux
What happens when there is high levels of iron
High Iron is sensed by protein called TfR2, HFE, HJV on hepatocytes
Hepcidin is produced by hepatocytes
Hepcidin binds to FNP1 on enterocytes to block iron absorption
Hepcidin binds to FNP1 on other cells to block iron absorption
What happens when there is low levels of iron
Hepcidin production is suppressed
What happens to hepcidin in infection and inflammation
IL-6 stimulates hepcidin transcription
Hepcidin acts on FNP1 on enterocytes to block iron absorption
Hepcidin acts on FNP1 on macrophages (that recycle iron) so iron is trapped within the macrophage
Why is hepcidin switched on in infection and inflammation
Bacteria needs iron to live
Stopping iron efflux limits the damage of bacteria
What can infection and inflammation result in
Anaemia of an chronic disease
