3. Physiology
        3.4. General physiology
            3.4.6. Electrolytes
3.4.6.3. Iron

Iron

[Ref: KB2:p198-201]

Major forms of dietary iron

NB:

Absorption of iron

Absorption of iron ions into enterocyte

Involves both:

NB:

Absorption of haem into enterocyte

From enterocyte

Iron in enterocyte can then be stored in cell or transported into blood

Storage

Iron (in ferric form) binds to apoferritin
--> Ferritin
--> Stored in enterocyte

Transport into blood

--> Iron (now in ferric form) binds to transferrin in blood

From blood into body cells

Transferrin binds to transferrin receptors
--> Endocytosis
--> Iron release within the cell and transferrin returned intact to ISF

Role of gastric acid in iron absorption

Low pH is important because it facilitates two things

  1. Reduction of dietary iron (ferric form) to ferrous form (Fe2+)
    * Also promoted by presence of dietary ascorbic acid
  2. Formation of soluble chelates
    * Ferric iron can bind with some substances (e.g. certain amino acids) forming soluble chelates
pH and solubility

Regulation of iron store

Also see Iron distribution

Lost of iron from body

Loss is relatively minor and unregulated

Main loss is in faeces as desquamated epithelial cells of the gut
= 0.5 to 1g day

Regulation of absorption

Control of iron absorption occurs at the enterocytes
--> i.e. mucosal block (aka mucosal intelligence)
* Full details are not known

If iron store is low
--> Plasma level of transferrin is high and saturation is low
--> More iron is passed from ferritin in mucosal cells to transferrin in blood

If iron store is adequate
--> Normal saturation
--> Iron remain in the enterocyte
--> Iron is lost when the cell is shed

Thus,

Proteins related to iron transport

Ferritin

Transferrin

Haemosiderin

Role of liver

= Major site of ferritin storage

When there is a demand for iron

Other notes



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