Iron is an essential trace element in human body, which is widely distributed in human body. Almost all tissues contain iron, with the highest content in liver and spleen and the highest content in lung. Iron is an important component of hemoglobin, an important element for transporting and exchanging oxygen in blood, a component of many enzymes and an activator of oxidoreductase. The physiological classification of iron is as follows: \ x0d \ x0d \ (1) Relationship between iron and enzymes: Iron participates in the synthesis of hemoglobin, myoglobin, cytochrome and cytochrome enzymes, and activates the activities of amber dehydrogenase and xanthine oxidase. The function of red blood cells is to transport oxygen. Each red blood cell contains about 280 million hemoglobin, and each hemoglobin molecule contains 4 iron atoms. The iron atoms in these hemoglobin are important components that really carry and transport oxygen. Myoglobin is where muscles store oxygen. Each myoglobin contains a heme, which can provide or supplement the deficiency of blood oxygen transmission during muscle exercise. \ x0d \ x0d \ cytochrome enzyme is an indispensable substance in the complex redox process in the body. With it, the electron transfer can be completed, and the hydrogen atoms removed by hemoglobin from the lungs and the oxygen transported can generate water in the trihydroxy acid cycle to ensure the metabolic needs of the body, and at the same time, energy can be released in the process to supply the needs of the body. Harmful substances such as hydrogen peroxide produced in the oxidation process can be destroyed by iron-containing catalase and peroxide, resulting in detoxification. \x0d\\x0d\(2) Iron participates in energy metabolism and hematopoietic function: Because iron exists in various forms in human body, its physiological functions are quite extensive. \ x0d \ x0d \ For example, hemoglobin can transport oxygen, myoglobin can store oxygen, cytochrome can transport electrons, and iron combined with various enzymes can decompose peroxides, detoxify and inhibit bacteria, and participate in the tricarboxylic acid cycle to release energy. The energy release effect of iron is related to the amount of iron accumulated in mitochondria of cell membrane. The more iron accumulated in mitochondria, the more energy released. \ x0d \ x0d \ Iron also affects the synthesis of protein and deoxyribonucleic acid, and participates in hematopoiesis and vitamin metabolism. Many studies have shown that the synthesis of deoxyribonucleic acid in the liver will be inhibited, the development of the liver will be slowed down, mitochondria and microparticles in hepatocytes and other cells will be abnormal, and the content of cytochrome C will be reduced, which will lead to the reduction of protein's synthesis and energy, and then anemia and height and weight dysplasia will occur. \ x0d \ x0d \ In addition, iron deficiency can also cause metabolic disorder of inorganic salts and vitamins in the body. \x0d\\x0d\(3) Iron and immune function: Iron participates in hematopoiesis, forms hemoglobin and myoglobin, and participates in oxygen carrying and transportation. Iron is also the active center of many enzymes. Both iron excess and iron deficiency will increase the chance of infection, because the growth and reproduction of microorganisms also need the presence of iron. \x0d\\x0d\ experiments show that the bactericidal ability of neutrophils decreases and the function of lymphocytes is damaged when iron deficiency occurs, and the immune function can be improved after iron supplementation. \x0d\\x0d\ In the process of phagocytosis of bacteria by neutrophils, it is necessary to rely on superoxide dismutase to kill bacteria, and this enzyme system can't play a role in iron deficiency. \x0d\\x0d\(4) Relationship between iron and other elements: The utilization of iron is blocked and the absorption of iron by intestine is inhibited in lead poisoning. The intracellular concentrations of copper and zinc in patients with iron deficiency anemia decreased and increased after iron supplementation. Oral cadmium in experimental mice can inhibit the absorption of iron in intestine, reduce serum ferritin and cause small cell hypochromic anemia, which can only be corrected by intravenous iron supplementation. \x0d\\x0d\ Small cell hypochromic anemia appears in uremia patients undergoing long-term hemodialysis, which can only be corrected by intravenous iron supplementation, which may be related to aluminum overload in serum and red blood cells. When the human body is short of copper, it not only reduces the absorption of iron, but also hinders the utilization of iron. \ x0d \ x0d \ In addition, iron deficiency will also affect the absorption of zinc. \x0d\\x0d\(5) Absorption, distribution and excretion of iron in human body: Iron is mainly absorbed by digestive tract through duodenum, and can also be absorbed by stomach and small intestine. Fe (II) is more easily absorbed than Fe (III), but most of the iron in food is Fe (III), so it must be reduced to Fe (II) in the stomach and duodenum to be fully absorbed. The absorbed bivalent iron is reoxidized to trivalent iron in intestinal mucosal epithelial cells, and stimulates duodenal mucosal cells to form a special protein-ferritin, which combines with trivalent iron to form ferritin. Iron in ferritin is decomposed into bivalent iron, which quickly enters the blood circulation, and the residual ferritin is still stored in intestinal mucosal cells. There are many factors affecting iron absorption, and both gastric acid and bile can improve iron absorption.