Physiology · Blood, hemostasis and basic immunity
Body iron balance !
- Regulation
- Exam priority: medium
The body cannot get rid of extra iron, so it controls how much the gut absorbs. The liver hormone hepcidin is the gatekeeper.
Updated 2026-11-01
Also called: Iron homeostasis, Hepcidin
See it in 3D: Duodenum · Liver · Spleen · Hip bone
What it is
An adult holds about 3–5 g of iron, most of it in hemoglobin. There is no regulated way to excrete iron; daily losses through shed cells and bleeding are small, so balance is set at absorption in the duodenum. Hepcidin, made by the liver, closes the iron exit channel ferroportin in gut cells and macrophages, linking iron supply to stores, erythropoiesis and inflammation.
How it works, step by step
- Dietary Fe³⁺ is reduced to Fe²⁺ by a duodenal reductase (helped by vitamin C and gastric acid).
- Fe²⁺ enters the enterocyte through DMT1; heme enters by its own carrier and is broken down inside.
- Iron is stored as ferritin in the cell, or exported through ferroportin and oxidized to Fe³⁺ (hephaestin).
- Transferrin carries Fe³⁺ in plasma; marrow erythroblasts take it up through transferrin receptor 1.
- Splenic and hepatic macrophages digest old red cells and return iron to transferrin through ferroportin.
- The liver senses iron and inflammation and secretes hepcidin, which internalizes and degrades ferroportin.
- Iron not exported is lost when enterocytes are shed after 2–3 days (the 'mucosal block').
Reference values (labs vary)
| Parameter | Value | Note |
|---|---|---|
| Total body iron | ≈3–5 g | more in men |
| Serum ferritin | ≈20–300 ng/mL men, ≈15–150 ng/mL women | rises with inflammation |
| Transferrin saturation | ≈20–50 % | |
| Daily absorption | ≈1–2 mg | up to several-fold in deficiency |
Approximate values for a healthy adult at rest; each laboratory sets its own ranges.
Three iron patterns
| Pattern | Ferritin | Transferrin saturation / TIBC | Hepcidin |
|---|---|---|---|
| Iron deficiency | Low | Low saturation, high TIBC | Low |
| Anemia of inflammation | Normal or high | Low saturation, low or normal TIBC | High |
| Hereditary hemochromatosis | High | High saturation (often >45 %) | Inappropriately low |
Clinical notes
- In adults, iron deficiency means blood loss until proven otherwise: heavy menses or gastrointestinal bleeding.
- Ferritin is an acute-phase reactant: a normal value does not exclude iron deficiency during inflammation.
- Absorption falls with phytates, tannins (tea, coffee), calcium and acid suppression, and rises with vitamin C and meat.
Test yourself
Think of the answer, then tap the question to see it.
Why does chronic inflammation cause anemia even when iron stores are full?
IL-6 raises hepcidin, which degrades ferroportin; iron stays trapped in macrophages and enterocytes, so transferrin saturation falls and the marrow is short of iron.
Why does hereditary hemochromatosis cause iron overload?
HFE and related defects keep hepcidin inappropriately low, so ferroportin stays open and the duodenum keeps absorbing iron that the body cannot excrete.
Why is ferritin the best single test of iron stores, and when does it mislead?
Serum ferritin reflects stored iron, and a low value is specific for deficiency. Because it rises with inflammation, liver injury and cancer, a normal value can hide deficiency.
Where does most of the iron used by the marrow each day come from?
From macrophages recycling iron from old red cells (≈20–25 mg/day); diet adds only 1–2 mg to replace losses.
See it in 3D
The structures of Durgical's 3D anatomy where it happens.
Related topics
- Absorption of iron, calcium and vitamin B12
- Anemia physiology and compensation
- Erythropoiesis and erythropoietin
- The red cell life cycle and the spleen
Related conditions
- Iron deficiency anaemia
- Hereditary hemochromatosis
- Abnormal uterine bleeding
- Upper gastrointestinal bleeding
In Biochemistry
Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.
Sources: 18.3 Erythrocytes (OpenStax (Rice University), 2022); Iron Deficiency and Microcytic Hypochromic Anemia (StatPearls (NCBI Bookshelf), 2024); Ferritin Blood Test (MedlinePlus (U.S. National Library of Medicine), 2024); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 33). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).
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Representative model, for educational purposes only.