Biochemistry · MU Pleven

64. Iron Metabolism. Role of Ferritine and Transferrine. Regulation.

Covers why iron matters in haem proteins and enzymes, then follows its path from dietary absorption in the duodenum through enterocyte export to transport by transferrin. It explains the storage role of ferritin and its link to hemosiderin, and how hepcidin regulates ferroportin under high and low iron, inflammation, erythropoiesis and hypoxia. The closing section sets out clinical patterns of iron deficiency anaemia, anaemia of chronic disease and hereditary haemochromatosis, with their ferritin, transferrin and serum iron findings.

Inside: 2 sections · 4 labelled pictures · 13 flashcards · 3 min

Topic 64 of 76 in the MU Pleven syllabus for Biochemistry (Medicine, Year 2). The free AceMed note covers it in 2 sections, about 450 words (3 min of reading), with 13 flashcards.

In this note

  1. Iron Metabolism. Role of Ferritine and Transferrine. Regulation.
  2. Iron Metabolism and Its Regulation

Iron Metabolism and Its Regulation

  • Iron is essential mainly because it’s needed for hemoglobin, myoglobin, and many enzymes (cytochromes, catalase, peroxidases). It acts as a reversible electron carrier, switching between Fe²⁺ (ferrous) and Fe³⁺ (ferric) states.
  • The body contains about 3–4 g of iron, and because there is no regulated excretion, the body prioritizes regulation of absorption rather than elimination.

Absorption of Iron

  • Iron from the diet appears in two main forms: – Heme iron (from meat; easily absorbed). – Non-heme iron (from plants; less efficiently absorbed).
  • Absorption occurs mainly in the duodenum. Non-heme Fe³⁺ must be reduced to Fe²⁺ before absorption (via ferrireductase and Vitamin C).
  • Inside enterocytes, Fe²⁺ can: – Be stored temporarily as ferritin, or – Be exported into the bloodstream through ferroportin (the only known iron exporter).
  • Once iron leaves the enterocyte, it is oxidized back to Fe³⁺ (by hephaestin or ceruloplasmin) and binds to transferrin for transport.

Transferrin

  • Transferrin is the main iron transport protein in plasma.

It keeps iron in soluble and non-reactive form, preventing free iron from generating free radicals (via Fenton reaction).

  • Transferrin delivers iron to: – Bone marrow (for hemoglobin synthesis). – Muscle (myoglobin). – Liver and macrophages (storage).
  • Cells express transferrin receptors. When iron is needed, receptor expression increases, pulling more transferrin-bound iron into the cell via receptor-mediated endocytosis.

Ferritin

  • Ferritin is the main intracellular iron storage protein.

It safely stores iron in a soluble, non-toxic form.

  • If iron stores become excessive, ferritin aggregates into hemosiderin, which is less accessible for release.
  • Serum ferritin reflects body iron stores and is clinically used to diagnose: – Low ferritin → iron deficiency. – High ferritin → inflammation or iron overload.

Regulation of Iron: Role of Hepcidin

  • The key regulator of iron metabolism is hepcidin, a hormone produced by the liver.
  • Hepcidin inhibits ferroportin, preventing iron export from: – Intestinal mucosal cells, – Macrophages, – Liver stores.
  • When hepcidin levels are high, iron becomes trapped inside cells, leading to low blood iron.
  • When hepcidin levels are low, ferroportin remains open, and iron is released into circulation, increasing serum iron.

When Hepcidin Increases

  • High iron stores
  • Inflammation (IL-6 induces hepcidin) → This causes the anemia of chronic disease, where iron is present but locked in storage.

When Hepcidin Decreases

  • Iron deficiency
  • Increased erythropoiesis (bone marrow needs iron for RBCs)
  • Hypoxia → This allows more iron absorption and release to support RBC production.

Clinical Importance

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