The circulatory system performs a transport function in the body of all warm-blooded animals, delivering nutrients and oxygen to the tissues. The transport of oxygen and carbon dioxide is carried out thanks to the red blood cells, which include an important substance - hemoglobin. In this article, we will consider the types and compounds of hemoglobin.
What is hemoglobin?
Hemoglobin is a component of red blood cells belonging to the group of proteins. It consists of 96% of the protein substance globin and 4% of a substance with a divalent iron atom - heme. 1 cell of its red blood cell contains about 280 million molecules, which forms the red color of the blood.
The main property of hemoglobin is the ability of iron to attach and split off gases, forming the movement of oxygen from the lungs to the tissues and carbon dioxide from tissues to the lungs. Thus, its role in the process of gas exchange in the body is indispensable.
The structure and types of hemoglobin in human blood
At different stages of the development of the human body, the composition of hemoglobin differs in the structure of the polypeptide chains. Depending on which polypeptide chains the hemoglobin structure contains, the types of hemoglobin in humans are as follows:
- Adult hemoglobin (HbA) is found in a dominant amount (about 98-99% of the total amount in the blood) in adults. HbA consists of 2 and 2 polypeptide chains. Each of the amino acid helices contains a heme component with an atom responsible for the affinity for the oxygen molecule. HbA has a lower ability to affinity with oxygen than other types of hemoglobin, but at the same time it is more resistant to fluctuations in pH and t.
- Fetal (HbF) is synthesized in the fetus even in the womb starting from 6-7 weeks of pregnancy, followed by its replacement with HbA. Already from 1 month of life, HbF synthesis slows down, the total blood volume increases, and HbA synthesis increases, which reaches the percentage of the blood composition of an adult by three years of a childβs life. Fetal hemoglobin from an adult differs in the composition of the globin chains; instead of a chain, a spiral type is present here. HbF, compared to HbA, has a lower degree of resistance to changes in blood pH and fluctuations in body temperature.
- Fetal (HbE). The primary form of respiratory protein is produced in the embryo even before the formation of the placenta (already in the first week of pregnancy) and lasts up to 6-7 weeks. The structure is distinguished by the presence of chains and ΞΆ types.
Pathological types of hemoglobin
In some cases, under the influence of genetic defects, an abnormal synthesis of hemoglobin cells occurs. Pathological types of hemoglobin from physiological ones differ in the composition of polypeptide bonds, or rather, their mutation.
As a result of DNA mutation, the synthesis of red blood cell components is carried out not with glutamine, but with valine amino acid. This βpersonnelβ substitution leads to the formation of a protein structure of type 2 with a βstickyβ area on the surface that can appropriate structures of its own kind. Thus, the polymerization of HbS molecules occurs and, as a result, the deposition of heavy and poorly transported red blood cells in blood vessels. This deviation is called sickle anemia.
Human hemoglobin levels
The content of protein respiratory structures in the blood in humans may vary depending on gender, age category, lifestyle and some other features, such as pregnancy.
Normal values ββof hemoglobin in the blood, not considered a pathological deviation:
- In men - 130-150 g / l.
- In women - 120-140 g / l.
- In children under the age of 100-140 g / l, and in the first month these values ββcan reach up to 220 g / l due to the increased concentration of fetal hemoglobin. In children from one year to 6 years old - 110-145 g / l, and from 6 years of age - 115-150 g / l, regardless of the gender of the child.
- During pregnancy, a decrease in the concentration of HbA to 110 g / l, which, however, is not considered anemia.
- In older people, the norm is considered to be a tendency to decrease by 5 units from the declared norm, depending on the patient's gender.
The age composition also differs in the composition of blood containing simultaneously different types of hemoglobin. For example, in an adult, the natural ratio is 99% HbA and up to 1% HbF. In children under one year of age, the percentage of HbF is significantly higher than in adults, which is explained by the gradual breakdown of the initial form of fetal hemoglobin.
Physiological forms
Since respiratory red pigment is continuously involved in gas exchange processes in the body, its main property is the ability to form compounds with molecules of various gases. As a result of such reactions, physiological types of hemoglobin are created, which are considered normal.
- Oxyhemoglobin (Hb) is a compound with an oxygen molecule. The process occurs in the respiratory system, in the alveoli of the lungs. Oxygenated red bodies stain red blood, which is called arterial and moves from the lungs to the tissues, enriching them with oxygen, which is necessary for oxidative processes.
- Deoxyhemoglobin (HbH) - restored hemoglobin is formed at the moment when the red bodies give oxygen to the tissues, but have not yet managed to take carbon dioxide from them.
- Carboxyhemoglobin (Hb) is formed by the removal of carbon dioxide from tissues and its removal to the lungs, completing the process of human breathing. Carboxyhemoglobin gives the venous blood a dark color - burgundy.
Pathological compounds
Red blood cells can attach not only the gases involved in the respiratory process, but also others, forming pathological types of hemoglobin, which are dangerous to human health and even life. These compounds have a low degree of decay, therefore, lead to oxygen starvation of tissues and serious respiratory disorders.
- Carbhemoglobin (HbCO) is an extremely dangerous compound in the blood of a person who has inhaled carbon monoxide. It blocks the ability of red bodies to transport oxygen to tissues. Even an insignificant concentration of carbon monoxide in the air of 0.07% can be fatal.
- Methemoglobin (HbMet) is formed by poisoning with nitrobenzene compounds, examples of which are aliphatic solvents of resins, esters, cellulose, which are widely used in the textile industry. When interacting with hemoglobin, nitrates transform the 2-valence iron contained in the heme into 3-valence iron, which also leads to hypoxia.
Diagnosis of hemoglobin
To identify the concentration of globin respiratory structures in human blood, qualitative and quantitative types of analyzes are performed. Hemoglobin is also tested for the amount of iron ions in it.
The main quantitative method for determining hemoglobin concentration today is colorimetric analysis. It is a study of the color saturation of a biological material when a special reagent is added to it.
Qualitative methods include blood testing for the content of the ratio of HbA and HbF types in it. A qualitative analysis also includes determining the amount of glycated hemoglobin molecules (compounds with carbon) in the blood - the method is used to diagnose diabetes.
Deviation of hemoglobin concentration from normal
HbA balance can vary both below and above the norm. In any case, this leads to negative consequences. With a decrease in HbA below the established norm, a pathological syndrome occurs, which is called "iron deficiency anemia". Expressed by lethargy, loss of strength, inattention. Negatively affects the nervous system, especially dangerous in childhood, as it is often the reason for the lag in psycho-motor development.
Elevated hemoglobin is not a separate disease, but rather a syndrome that indicates various pathologies, such as diabetes mellitus, pulmonary failure, heart disease, kidney disease, an excess of folic acid or B vitamins, oncology, etc.