Iron Metabolism Notes PDF

# TRACE ELEMENTS ## IRON ### Dietary Sources: - The liver, heart, kidney, spleen, meat and egg yolk are very good sources of iron. - Molasses, dates, legumes, vegetables and whole cereals are good sources. ### Absorption: - variable and dynamic process - in the duodenum and upper jejunum - The am...

# TRACE ELEMENTS ## IRON ### Dietary Sources: - The liver, heart, kidney, spleen, meat and egg yolk are very good sources of iron. - Molasses, dates, legumes, vegetables and whole cereals are good sources. ### Absorption: - variable and dynamic process - in the duodenum and upper jejunum - The amount of iron absorbed compared to the amount ingested is typically low, but may range from 5%-35% ### Factors Influence Iron Absorption: - **Ascorbate and Citrate:** Increase iron uptake in part by increasing the solubility of the metal in the duodenum. - **Phytates in Wheat and Some Other Cereals and Tannins in (Non-herbal) Teas:** Decrease the solubility of iron; thus inhibiting its absorption. ### Mechanism: - A ferric reductase enzyme on the enterocytes' brush border and Duodenal Cytochrome b (DCYTB), reduces ferric Fe3+ to Fe2+. - Ferrous ions are transported across the enterocyte apical membrane by The Divalent Metal Transporter 1 (DMT1), (a proton coupled divalent ion transporter. - Iron effluxes from the enterocyte basolateral membrane through ferroportin and is oxidised by a membrane bound ferroxidase, hephaestin, yielding ferric ions that are then bound by plasma transferrin for distribution around the body via the blood. ### Regulation Of Iron Absorption: - **Principle Regulatory Mechanism:** Involves sensing of high body iron stores or low erythroid iron requirements by the liver, which produces an inhibitory peptide, hepcidin, that acts on the intestine to decrease iron absorption. - **Dcytb and DMT1 levels:** Are also affected, most likely in response to altered iron levels in enterocytes caused by hepcidin's action on iron efflux through ferroportin. ### Distribution And Functions: - The total iron in the body is about 4g. It is present in the body in the 2 forms: 1. **Functional Forms (75%)** - These are mostly in the form of *hemoproteins* such as *hemoglobin*. 2. **Nonfunctional Forms (25%)** - These are transport and storage forms of iron. - They are *non-hememetalloproteins*. - **Transferrin:** This is the *transport* form of iron in the blood plasma. - **Ferritin:** This is the chief *storage* form of iron in the tissues. It is present in the liver, kidneys, spleen, bone marrow, and intestinal mucosal epithelium. - **Hemosiderin:** This is present in iron stores when the body contains excess iron. - **Lactoferrin:** It is present in milk; it contains iron that is bound to a *glycoprotein*. It facilitates iron transport and storage in milk ### Blood Iron: 1. **In Red Cells:** The erythrocytes contain hemoglobin, which contains 3.4 mg of iron per gram. 2. **In Plasma:** - **Transferrin:** The plasma iron concentration is 50-150 µg/dL. Iron is carried by a glycoprotein, transferrin, which carries 2 atoms of ferric iron per molecule. - It is synthesized in the liver. - Low degree of transferrin saturation by ion facilitates iron release from the mucosal cells. - **Total Iron-Binding Capacity (TIBC):** Transferrin may carry up to 250-400 µg of iron per dL plasma. This means that, on the average, only about 30% of the TIBC is saturated. - **Unsaturated Iron-Binding Capacity (UIBC):** About 60-70% of transferrin is unsaturated. - **Iron Deficiency Anemia:** The plasma iron decreases while the TIBC tends to increase. - **Ferritin:** Plasma contains very low concentrations of ferritin, which is a very good index of iron storage. It decreases in iron deficiency and increases in hemosiderosis. ### Abnormalities Of Iron Metabolism: #### I. Iron Deficiency Anemia - **Characteristics:** Microcytic and hypochromic red blood cells. Excess menstrual flow or gastrointestinal bleeding. - **Treatment of Iron Deficiency Anemia Includes:** - Treatment of the cause of bleeding. - A preparation of iron (iron dextran) for intramuscular injection has been used in patients who cannot tolerate or absorb oral iron. - **Caution must be taken when iron is given parenterally because of the possibility of oversaturation of tissues with resultant production of hemosiderosis.** #### II. Iron Toxicity (Hemosiderosis or Hemochromatosis) - **The body is unable to excrete a large load of iron. Iron differs from most other minerals in that its quantity in the body is controlled by regulating its absorption rather than excretion.** ##### Causes: - In patients of aplastic or hemolytic anemia who have received many blood transfusions over a period of years. - Inherited anomaly of iron absorption, some persons has excessive ability to absorb iron which produces iron accumulation after many years. - Overdose of parenterally administered iron. - **In all above conditions, hemosiderin accumulates in different tissues, a condition known as hemosiderosis.** ### Hemochromatosis - **Hemosiderosis** with injury to involved tissues as manifested by cellular degeneration and **fibrosis**. - **Clinical manifestations:** Include *bronzed pigmentation of the skin, liver cirrhosis and pancreatic fibrosis, leading to diabetes mellitus (bronze diabetes)*. - **Serum iron** is elevated and **transferrin** becomes 70-90% saturated with iron. ## IODINE ### Dietary Sources: - The best sources are *seafood*. Vegetables and fruits grown near seaboard contain high concentrations of iodine. Iodized table salt is now available to prevent iodine deficiency. ### Absorption And Distribution: - *Organic iodine* is partly converted to *inorganic iodide* before absorption. Inorganic iodine ($I_2$) and iodide ($I^{-}$) are absorbed via skin, lungs and intestine. ### Distribution: 1. **Thyroid Gland (30%-50%)** - Concentrate iodide from the blood. *Thyroglobulin* contains iodide in the form of monoiodotyrosine (MIT), diiodotyrosine (DIT), triiodothyronine ($T_3$) and tetraiodothyronine or thyroxine ($T_4$), mostly the last two. 2. **Other tissues and body fluids (50%-70%)** - Iodide is partly in organic combination, $T_3$ and $T_4$ and *their metabolites*, and partly in the form of inorganic iodide (NaI and KI). Inorganic iodide markedly decreases in iodide deficiency. ### Functions: - Thyroid hormones. ### Excretion: 1. **In urine (70%)**: This is mainly in the form of *inorganic iodine*. - $T_3$ and $T_4$ are *not* present normally in urine being transported in conjugation with plasma proteins. 2. **In feces (30%):** This represents the *unabsorbed* iodine of diet and iodine excreted in saliva, bile and intestinal secretions. ### Iodine Deficiency: - Thyroid hypertrophy (*goiter*) occurs if iodine deficiency is prolonged.