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Iron Absorption & Role - An Overview Iron is an essential element of various metabolic processes in animals including DNA synthesis, electron transport, and oxygen transport. Unlike other minerals, iron levels in the body are controlled only by absorption. The mechanism of iron excretion is an unregulated process arrived at through loss in sweat, menstruation, shedding of hair and skin cells, and through rapid turnover and excretion of enterocytes. In the animal's body, iron exists mainly in erythrocytes as the heme compound haemoglobin, to a lesser extent in storage compounds (ferritin and hemosiderin) and in muscle cells as myoglobin. Iron also is found bound to proteins (hemoprotein) and in non-heme enzymes involved in oxidation-reduction reactions and the transfer of electrons (cytochromes and catalase). There are two types of absorbable dietary iron: heme and non-heme iron. Ÿ
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Heme iron, derived from haemoglobin and myoglobin of animal food sources (meat, seafood, and poultry), is the most easily absorbable form (15% to 35%) and contributes 10% or more of our total absorbed iron. Non-heme iron is derived from plants and iron-fortified foods and is less-well absorbed.
Despite its relative abundance in the environment and the relatively low daily iron requirements, iron is often a growth-limiting nutrient in the animal's diet. One reason for the lack of adequate iron absorption is that upon exposure to oxygen, iron forms
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Dr. Yogesh Paharia B.V.Sc , M.V.Sc ( Nutrition )
highly insoluble oxides which are unavailable for absorption in the gastrointestinal tract. Enterocytes contain apical membrane-bound enzymes whose activity can be regulated and which function to reduce insoluble ferric (Fe3+) to absorbable ferrous (Fe2+) ions. Iron absorption is a rapid process. Following the administration of a radioactive dose of iron into the l u m e n of t h e p rox i m a l s m a l l intestine, radioactivity usually appears in the circulation within 15 s, and within minutes, 60%–80% of the total amount ultimately absorbed is transferred into the body. This initial phase of rapid iron uptake is followed by a slower rate of transfer that continues for 12–48 h. It is likely that this iron was initially retained within enterocytes in ferritin. Some iron stored in ferritin, however, never makes it into the circulation since it is lost when mucosal cells are exfoliated at the end of their lifespans. 83 During iron deficiency, not only is the total amount of iron absorbed greater but also the fraction retained within the enterocyte is much smaller. Although iron deficiency is a relatively common problem, it is not the only extreme of the iron-balance spectrum that must be avoided. Iron overload can be par ticularly damaging to the heart, liver, and endocrine organs. Excess ferrous iron forms free hydroxyl radicals via the Fenton reaction that cause damage to tissues through oxidative reactions with lipids, proteins, and nucleic acids. Thus, dietary iron absorption and factors affecting bio
availability in the body are tightly regulated where possible. Cellular The absorption of most dietary iron occur s in the duodenum and proximal jejunum and depends heavily on the physical state of the iron atom. At physiological pH, iron exists in the oxidized, ferric (Fe3+) state. To be absorbed, iron must be in the ferrous (Fe2+) state or bound by a protein such as heme. The low pH of gastric acid in the proximal duodenum allows a ferric reductase enzyme, duodenal cytochrome B (Dcytb), on the brush border of the enterocytes to convert the insoluble ferric (Fe3+) to absorbable ferrous (Fe2+) ions. The gastric acid production plays a key role in plasma iron homeostasis. When protonpump inhibiting drugs such as omeprazole are used, iron absorption is greatly reduced. The duodenal pH-dependent process of iron absorption is inhibited or enhanced by certain dietary compounds. Ÿ
Inhibitors of iron absorption include Phyate which is a compound found in plant-based diets that demonstrate a dosedependent effect on iron absorption. Polyphenols are found in black and herbal tea,
Poultry Planner | Vol. 22 | No.07 | September - 2020
