Iron metabolism: haemoglobin synthesis

2021-05-07 11:21 PM

When red blood cells are destroyed, the haemoglobin from these cells is introduced into the monocyte-macrophage cells. The iron released and stored primarily in ferritin is used when needed for the formation of new haemoglobin.

Iron is essential not only for haemoglobin synthesis but also for other molecules in the body (e.g., myoglobin, cytochromes, cytochrome oxidase, peroxidase and catalase), so it is important to understand the iron mechanism used in the body. body. The total amount of iron in the body is about 4-5 grams, 65% in haemoglobin, about 4% in myoglobin, 1% in heme-containing compounds that catalyse intracellular oxidation reactions, 0.1% binds with transferrin, 15-30% bound to ferritin, is reserved for later use in the intermuscular and hepatic parenchymal inter-retinal system.

Transporting and storing iron

The figure shows the transport, storage and metabolism of iron in the body. After being absorbed from the small intestine, iron is transferred to plasma and attached to β-protein, apo transferrin, to be transferred and transported in the bloodstream. Iron is loosely linked to the drive and can be released to any tissue in the body. Excess iron is stored in the liver parenchyma and less in the retinal system of bone marrow endothelial cells.

Figure. Transporting and metabolizing iron

In the cytoplasm. Iron binds apoferritin to form ferritin. Apoferritin weighs about 460,000 Da and is bound to large amounts of iron in the root clusters; therefore, a molecule may have either large or small amounts of iron, which is called storage iron.

There is a smaller reserve of iron, insoluble in the form of hemosiderin, which is especially needed when excess iron exceeds apoferritin storage capacity. Hemosiderin is a large molecule that can be seen by microscopy, whereas ferritin is very small and dispersed, so it must be observed with a magneto scope.

When plasma iron levels are low, some of the iron in ferritin storage tanks is easily released and transported as plasma transferrin to areas of the body where it is needed. One characteristic of the transferrin molecule is that it strongly binds to the cell membrane receptors of erythroblasts (erythroblasts) in the bone marrow. Then, iron is introduced into the erythroblasts by endocytosis (phagocytosis). Transferrin delivers iron directly to the mitochondria (the mitochondria), where the heme is synthesized. In people who do not have an adequate amount of transferrin in the blood, a lack of iron transport into erythroblasts can cause severe hypochromic anaemia (hypo chromatic anaemia, that is, red blood cells much less haemoglobin than normal).

When red blood cells have lived for about 120 days and are destroyed, the haemoglobin from these cells is introduced into monocyte-macrophage (mononuclear phagocytes). The iron released and stored primarily in ferritin is used when needed for the formation of new haemoglobin.

Daily loss of iron. Men excreted about 0.6 mg of iron per day, mainly in the faeces. An additional amount of iron is lost when bleeding occurs. For women, menstrual blood loss causes long-term losses of iron stores with an average of about 1.3 mg/day.

Absorb iron from the intestine

Iron is absorbed from all sections of the digestive tract, mostly by the following mechanism. The liver secretes a moderate amount of apo transferrin into the bile, which flows through the bile ducts into the duodenum. Here, apo transferrin combines with free iron and is also present in a number of iron compounds, such as haemoglobin and meat-based myoglobin, two of the most important sources of dietary iron. This combination produces transferrin. The order in which it happens is, binds to receptors in the membranes of the intestinal epithelial cells. Then, by pinocytosis (humidifier), the molecular transferrin, carrying the iron door, is absorbed into the epithelial cells and then into the blood capillaries under these cells in the form of transferring plasma. Iron is absorbed from the gut very slowly, with a maximum rate of only a few milligrams per day. This means that even when large amounts of iron are present in food, only a small percentage can be absorbed.

Regulates total body iron by Controlling absorption. When the body becomes iron-saturated, basically all apoferritin in the storage area has been combined with iron, the rate of absorption of additional iron from the intestinal tract is drastically reduced. Conversely, when the stored iron has become depleted, the rate of absorption can be five times faster or more than the normal time. Thus, the total body iron is regulated mainly by varying the absorption rate.

Red blood cell life is about 120. When red blood cells are supplied from the bone marrow into the circulatory system, they typically circulate for an average of 120 days before being destroyed. Although mature, red blood cells do not have a nucleus, mitochondria, or endoplasmic reticulum. They have cytoplasmic enzymes that are capable of metabolizing glucose and form small amounts of adenosine triphosphate (ATP). These enzymes have the roles of (1) maintaining the mobility of the membrane, (2) maintaining the transmembrane transport of ions, (3) keeping the iron of haemoglobin in the cell as II iron. Non-ferrous iron and (4) prevent oxidation of proteins in red blood cells. Even so, the old red blood cells metabolic systems gradually become less active and the cells become more fragile, perhaps because the red blood cells are worn out.

When the red blood cell membrane becomes fragile, the cells rupture while passing some point in the cycle. Many people destroy red blood cells in the spleen, where they pass through the red marrow of the spleen. There, between the structural rafts of the red marrow, most cells must pass, only 3 micrometres wide, compared with 8 micrometres in diameter of RBC. When the spleen is removed, the number of abnormal old red blood cells circulating in the blood increases dramatically.

Destruction of Haemoglobin by macrophages. When red blood cells rupture and release haemoglobin, the haemoglobin is phagocytosed almost immediately by macrophages in many parts of the body, especially hepatic Kupffer cells and macrophages of the spleen and bone marrow. . Over the course of a few hours to a few days, macrophages release iron from haemoglobin and return it to the bloodstream, to be transported by transferrin either to the bone marrow producing new red blood cells or to the liver and other tissues to be stored as ferritin.

The porphyrin fraction of the haemoglobin molecule is metabolized by the macrophages, through a series of stages, into the bile pigment bilirubin, which is introduced into the bloodstream and then eliminated from the body by secretion through the liver into the bile.

 

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