Iron Metabolism Flashcards
State three biological processes that are reliant on iron.
oxygen transport, DNA synthesis, electon transport
(a) Dietary iron can exist in two forms: ____________.
(b) Which is more readily absorbed?
(a) heme iron [found in animal products] and non-heme iron [found in plant-based foods]
(b) Heme iron is more readily absorbed.
Briefly explain the haem pathway of iron absorption.
✓ Haem is absorbed into enterocyte as intact metalloprotein through specific receptors. It is taken up by enterocytes (intestinal cells) via a specific receptor known as the heme carrier protein 1 (HCP1) or heme transporter.
✓ Once inside the enterocyte, the heme molecule is broken down by the enzyme heme oxygenase.
✓ Heme Oxygenase: This enzyme cleaves the heme ring to release ferrous iron (Fe²⁺), biliverdin, and carbon monoxide.
✓ The released ferrous iron can then be utilized by the body, stored as ferritin within the enterocyte, or exported into the bloodstream via ferroportin.
[Diagram 1] [Diagram 2] [Diagram 3]
Outline the non-haem pathway of iron absorption.
(1) Non-heme iron exists in both ferric (Fe³⁺) and ferrous (Fe²⁺) forms. Ferric iron must be reduced to ferrous iron before absorption.
(2) This reduction is faciliated by duodenal cytochrome B reductase (DcytB) on the apical surface of enterocytes, with the help of reducing agents like vitamin C and the acidic environment provided by stomach HCl.
(3) Ferrous iron is then transported into enterocytes via the divalent metal transporter 1 (DMT1).
Explain the role of hephaestin in iron metabolism.
Hephaestin is a transmembrane protein that is primarily expressed in the enterocytes of the small intestine, particularly in the villi where iron absorption occurs.
It acts as a copper-dependent ferroxidase, converting ferrous iron (Fe²⁺) to ferric iron (Fe³⁺). This oxidation is crucial because ferric iron is the form that can be transported in the bloodstream. [Diagram 1] [Diagram 2]
List three biochemicals that enhance the absoption of non-heme iron.
ascorbic acid (vitamin C), amino acids, organic acids, simple sugars, cysteine
List three biochemicals that inhibit the absoption of non-heme iron.
phosphates, polyphenols, phytates, calcium, zinc, tanin
Further notes:
What are phytates?
Phytates, also known as phytic acid, are naturally occurring compounds found in plant seeds. They serve as the primary storage form of phosphorus in many plants.
Found in: Phytates are present in a variety of plant-based foods, including grains, legumes, nuts and seeds.
Anti-nutrient properties: Phytates are often referred to as “anti-nutrients” because they can bind to essential mineral such as iron, zinc, calcium, and magnesium, reducing their absorption in the digestive tract.
Hepcidin is a key hormone in the regulation of iron homeostasis, often referred to as the “master iron regulator”. Where is it produced?
liver
Explain the mechanism of action of hepcidin.
➤ Hepcidin exerts its effects by binding to ferroportin, the only known iron exporter located on the surface of enterocytes, macrophages, and hepatocytes.
➤ When hepcidin binds to ferroportin, it triggers the internalization and degradation of ferroportin. This process reduces the amount of iron released into the bloodstream from these cells.
What effect does hepcidin have on intestinal iron absorption?
Hepcidin decreases the absorption of dietary iron from the intestine by degrading ferroportin on enterocytes.
How does hepcidin affect iron recycling?
Hepcidin reduces the release of iron from macrophages that recycle iron from senescent red blood cells.
How does erythropoietic activity influence hepcidin levels?
Increased erythropoietic activity, such as during anemia or hypoxia, decreases hepcidin levels to allow more iron to be available for red blood cell production.
What triggers the production of hepcidin?
What is the primary protein responsible for transporting iron in the plasma?
transferrin
In what form does transferrin bind to iron?
Ferric form (Fe3+)
