Hemoglobin
Hemoglobin is a vital protein found in red blood cells (erythrocytes) responsible for transporting oxygen throughout the body. Composed of four polypeptide chains—two alpha and two beta—hemoglobin also contains heme groups that include iron, which gives red blood cells their characteristic color. In healthy adults, hemoglobin levels typically range from 12–16 grams per deciliter in women and 14–18 grams in men. While a small percentage of oxygen is carried by plasma, hemoglobin is the primary transporter, binding with oxygen in the lungs to form oxyhemoglobin and delivering it to tissues and organs.
Red blood cells have a lifespan of 80 to 120 days, after which they are destroyed and their hemoglobin is broken down into heme and globin, with iron either recycled for new red blood cell production or stored in the body. Anemia, a condition characterized by low hemoglobin levels, can result from insufficient red blood cell production or increased destruction, leading to reduced oxygen delivery to tissues. Hemoglobin counts are typically assessed through complete blood count tests, providing valuable insights into an individual’s health. Interestingly, a rare variant known as "Haemoglobin Bonn" has been identified, which may affect oxygen measurement in clinical settings.
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Subject Terms
Hemoglobin
Hemoglobin, the principal carrier of oxygen inside the body, is found in the red blood cells. Red blood cells are called erythrocytes. Plasma also contributes to the distribution of oxygen. The quantity of hemoglobin generally found in a woman is 12–16 grams per decaliter of blood, and in men, the quantitative measurement is 14–18 grams per decaliter. A normal level for a woman is considered to be 13 to 14 grams per 100 ml, and 15 grams per 100 ml for men.
Hemoglobin is a molecule that is formed when red blood cells are manufactured. This takes place in the bone marrow. Within each red blood cell, there are around 280 million hemoglobin molecules. The word hemoglobin is a composite of two words: heme and globin, representing a nonprotein and protein, respectively. Hemoglobin may be written in its abbreviated form as HgB or Hb. Reference to hemoglobin and hematocrit is abbreviated as H and H.
Background
A hemoglobin molecule is made up of four protein chains. The chains are known as alpha or beta chains, with two of each. In addition to alpha and beta proteins, a hemoglobin molecule consists of heme, a specific nonprotein group found in hemoglobin. It consists of iron and protoporphyrin and is structured according to a complex ring comprising four groups or pyrols. These further contain four carbons and a nitrogen.
Structure of Heme and Globin. Heme is comprised of a ferrous atom (Fe++) and is placed at the center of the ring structure. There are double bonds that are not static but keep moving. Globin is a subunit of hemoglobin made up of a complex set of chains. The polypeptide chain of a hemoglobin molecule is formed around a heme group or pocket. There are four polypeptide chains. The structural format of hemoglobin subunits is a tetrahedral arrangement.
During different periods of life, the hemoglobin chain experiences changes. From embryo to fetus to adult, the dominant globin chain may differ. Although the tetramer aspect of globin polypeptide chains is constant, the embryonic and fetal stages produce different types of hemoglobin, until the adult hemoglobin HbA comes into effect.
Oxygen Transport. While plasma assists in a small section of oxygen transport in the bloodstream, hemoglobin performs the main work. The ratio is 2 percent oxygen carried by plasma as opposed to the majority 98 percent transported by hemoglobin. One iron atom or unit of hemoglobin iron carries one molecule of oxygen. Oxyhemoglobin is the term for oxygen and hemoglobin when they bind and are transported together. This occurs as a chemical reaction with the meeting of hemoglobin and oxygen. Structural changes to the hemoglobin take place as a result, with the iron of hemoglobin possessing a greater affinity to attracting oxygen.
Overview
Red Blood Cells. Erythrocyte is the term for a red blood cell. Thirty-three percent of the erythrocyte is made up of hemoglobin. As hemoglobin contains red pigment, the blood cells gain their red color. Whereas the primary function of red blood cells is to carry oxygen to body tissues and organs, white blood cells or leukocytes are blood cells that function as part of the immune system of the body.
Red blood cells are destroyed regularly, given the ability of the erythrocytes to last for 80 to 120 days. They are destroyed by macrophages (of the reticuloendothelial or macrophage system). This occurs at an extremely rapid rate, with between two and ten million red cells per second undergoing destruction. At the same time, new cells are regenerated. At the time that the red cells are being destroyed, the hemoglobin is released. When this occurs, it generates a breaking down of hemoglobin into heme and globin. A further breakdown takes place as the heme splits into iron and protoporphyrin. Protoporphyrin undergoes a change into bilirubin, associated with the liver and bile excretion. Iron, on the other hand, may experience two different routes or functions. New erythrocytes (red blood cells) may be formed from the iron. Alternatively, if the body possesses a high level of iron, the excess may be carried to the bone marrow, liver, or spleen. The iron may be stored in these body parts.
Iron. The significant component of hemoglobin is the protein that contains iron. All red blood cells possess this. The binding of oxygen in the lungs to the red blood cells, and then transporting these to body tissues and organs, is facilitated by the iron protein of hemoglobin.
Anemia is linked to a low level of hemoglobin. When insufficient red blood cells are formed, there may be a corresponding level of oxygen carried inside the body to the tissues requiring supply. The lack of blood cells or a heightened amount of blood cells being destroyed may contribute to a reading of anemia. A deficient production and supply of hemoglobin may likewise affect hemoglobin levels and cause anemia. When an individual has an iron deficiency, a lack of hemoglobin may cause each cell to be less developed. Thus, while there may be a normal amount of red blood cells, there may not be enough hemoglobin being produced.
Blood Count. When a blood test is required to gain a blood count reading, the amount of red blood cells per cubic millimeter must be ascertained. Additionally, the shape and size of the cells are measured and the amount of hemoglobin found in the cell is checked. A hemoglobin count is usually combined in a complete blood count test (CBC).
In 2008, a rare type of hemoglobin was discovered by scientists. Named "Haemoglobin Bonn" due to its discovery at the University of Bonn, this hemoglobin type optically presents as carrying little oxygen. Appearing as a possible health defect, scientists determined that the "Haemoglobin Bonn" distorts the oxygen level measurement.
Bibliography
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