The Absorption of Iron and Intestinal Disease Flashcards
Which ion is ferrous iron and which is ferric?
ferrous = 2+ ferric = 3+
Where is dietary iron absorbed by?
What is it transported around the blood with/
duodenal enterocytes
transferrin
Where can iron by transported to and what does it do in each place?
bone marrow - added to Hb with RBC’s
liver/spleen - storage
muscle - stored in myoglobin
cells - utilises iron for enzymes, and other cellular functions
There are no mechanisms in the body to remove iron, although a few milligrams are lost daily in: - - - - -
blood - menstruation faeces - cells urine - cells skin - cells sweat - more in athletes
What are the two types of dietary iron?
inorganic iron = Fe3+
haem = Fe2+
Both forms of dietary iron are found highly bound to food proteins and are firstly released from them and kept soluble by …….. …… and ………
gastric acid
pepsin
How does haem enter the enterocyte?
What happens to it then?
via the transporter HAEM CARRIER PROTEIN (HCP1).
it is subsequently degraded by haem oxygenase to liberated Fe2+
What has to happen to inorganic iron before it can absorbed by enterocytes? Why?
How does it then enter the enterocyte?
Fe3+ is non-absorbable
It needs to be reduced to Fe2+, this is achieved by DcytB (ferric reductase). This can also be aided by gastric acid.
It enters the enterocyte via the transporter DMT1 (divalent metal transporter-1)
What 3 things does the Fe2+ do once inside the enterocyte?
stored as ferritin (Fe3+)
used by the cell
converted to Fe3+ by hephaestin, transported out by ferroportin, incorporated into transferrin
What effect does hepcidin have on iron levels?
When is it produced?
it decreases them
released when iron is high
Where does hepcidin act?
What effects does hepcidin have?
It internalises and degrades ferroportin so the iron cannot be transported out of the cells.
Ferroportin is found on, and hence hepicidin acts on:
- macrophages, enterocytes, hepatocytes
What is hepcidin synthesis suppressed by?
When is hepcidin synthesis induced?
- iron deficiency, anaemia, hypoxaemia, accelerated erythropoesis
- high iron stores, inflammation
Describe the basis of anaemia of chronic inflammation
During inflammation interleukin-6 levels are raised
This is a stimulator for hepcidin synthesis
Ferroportin transporters are degraded
Iron transport is decreased.
Iron levels decrease
Describe how hypoxaemia leads to increased iron levels.
Low O2 surpasses hepcidin synthesis
There is an increased uptake of dietary iron, iron is released from hepatocytes and macrophages
What 2 things occur when iron levels are low?
- hepcidin levels low, so ferroportin is rich on the basolateral surface to permit more iron release
- DMT1 is rich on the apical surface to permit more iron absorption
