Hemoglobin

hemoglobin /he·mo·glo·bin/ (he´mo-glo?bin) the oxygen-carrying pigment of erythrocytes, formed by developing erythrocytes in the bone marrow; a hemoprotein made up of four different polypeptide globin chains that contain between 141 and 146 amino acids. Hemoglobin A is normal adult hemoglobin and hemoglobin F is fetal hemoglobin. Many abnormal hemoglobins have been reported; the first were given capital letters such as hemoglobin E, H, M, and S, and later ones have been named for the place of discovery. Homozygosity for hemoglobin S results in sickle cell anemia, heterozygosity in sickle cell trait. Symbol Hb.

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fetal hemoglobin  that forming more than half of the hemoglobin of the fetus, present in minimal amounts in adults and abnormally elevated in certain blood disorders.

mean corpuscular hemoglobin  (MCH) the average hemoglobin content of an erythrocyte.

muscle hemoglobin  myoglobin.

reduced hemoglobin  that not combined with oxygen.

hemoglobin S  the most common abnormal hemoglobin, with valine substituted for glutamic acid at position six of the beta chain, resulting in the abnormal erythrocytes called sickle cells, and causing sickle cell anemia.

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he·mo·glo·bin (hm-glbn)

n. Abbr. Hb, Hgb

The red respiratory protein of red blood cells that transports oxygen as oxyhemoglobin from the lungs to the tissues, where the oxygen is readily released and the oxyhemoglobin becomes hemoglobin.

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Hemoglobin (Hb)

An iron-containing pigment of red blood cells composed of four amino acid chains (alpha, beta, gamma, delta) that delivers oxygen from the lungs to the tissues of the body.

Mentioned in: Anemias, Anoxia, Antianemia Drugs, Biliary Atresia, Blood Gas Analysis, Carbon Monoxide Poisoning, Coombs' Tests, Cyanosis, Erythroblastosis Fetalis, Haptoglobin Test, Hematocrit, Hemoglobin Test, Hemoglobinopathies, Iron Deficiency Anemia, Jaundice, Liposuction, Multiple Myeloma, Neonatal Jaundice, Platelet Function Disorders, Porphyrias, Sickle Cell Disease, Thalassemia, 2,3-Diphosphoglycerate Test

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hemoglobin,

n a protein-iron compound in red blood cells that carries oxygen from the lungs to body cells. The normal hemoglobin levels in the blood are 12 to 16 g/dL in women and 13.5 to 18 g/dL in men.

Hemoglobin.

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hemoglobin (hē´mōglōbin),

n the oxygen-carrying red pigment of the red blood corpuscles. It is a reddish, crystallizable conjugated protein consisting of the protein globulin combined with the prosthetic group, heme.

hemoglobin A (HBA),

n a normal hemoglobin. Also called
adult hemoglobin.

hemoglobin estimation,

n a determination of the hemoglobin content of the blood. By the Sahli method, 14 to 17 g/100 mL of blood is normal, and 15.1 Sahli units are taken as 100% for estimation of hemoglobin percentages.

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hemoglobin

an allosteric protein found in erythrocytes that transports molecular oxygen (O₂) in the blood. Symbol Hb.

Oxygenated hemoglobin (oxyhemoglobin) is bright red in color; hemoglobin unbound to oxygen (deoxyhemoglobin) is darker. This accounts for the bright red color of arterial blood, in which the hemoglobin is about 97% saturated with oxygen. Venous blood is darker because it is only about 20-70% saturated, depending on how much oxygen is being used by the tissues.

The affinity of hemoglobin for carbon monoxide is 210 times as strong as its affinity for oxygen. The complex formed (carboxyhemoglobin) cannot transport oxygen. Thus, carbon monoxide poisoning results in hypoxia and asphyxiation.

Another form of hemoglobin that cannot transport oxygen is methemoglobin, in which the iron atom is oxidized to the +3 oxidation state. During the life span of a red cell, hemoglobin is slowly oxidized to methemoglobin. At least four different enzyme systems can convert methemoglobin back to hemoglobin. When these are defective or overloaded, methemoglobinemia, in which high methemoglobin levels cause dyspnea and cyanosis, may result.

As red cells wear out or are damaged, they are ingested by macrophages of the reticuloendothelial system. The porphyrin ring of heme is converted to the bile pigment bilirubin, which is excreted by the liver. The iron is transported to the bone marrow to be incorporated in the hemoglobin of newly formed erythrocytes.

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hemoglobin A_1c

see glycosylated hemoglobin (below).

carcass hemoglobin tests

include hemoglobin extraction test, hemoglobin-pseudoperoxidase test. Used on suspect meat to determine if it has been properly bled out; poor bleeding is an indication of fever or septicemia.

hemoglobin concentration

varies with the hematocrit; determined by several methods. Assesses the oxygen-carrying capacity of blood.

cyanotic hemoglobin malformations

insufficient oxygenated hemoglobin is received in the peripheral capillary beds resulting in blue discoloration of tissues, and an incapacity of the body to maintain a life-sustaining level of activity.

glycosylated hemoglobin

hemoglobin A with a glucose moiety attached to the amino terminal valine of the beta chain. This type of hemoglobin is made at a slow constant rate during the life span of the erythrocyte. Increased levels correlate with glucose intolerance in diabetes. With adequate insulin treatment, levels return to the normal range and periodic assays can be helpful in evaluating effective control of diabetes mellitus. Called also hemoglobin A_1c.

glycosylated hemoglobin test

measurement of the percentage of hemoglobin A molecules that formed a stable ketoamine linkage between the amino terminal valine residue of the beta chain and a glucose moiety; used to assess diabetic control.

hemoglobin-oxygen dissociation curve

the incremental increase in oxygen saturation of the hemoglobin with each unit increase of the partial pressure of oxygen in the blood. Any factor that shifts the curve to the right will automatically reduce the concentration of O₂ held by the hemoglobin and increase the rate of its delivery to tissues.

urine hemoglobin

see hemoglobinuria.

hemoglobin variants

the globin part of hemoglobin is composed of a large number of amino acids and the hemoglobins are therefore susceptible to a great many variations. In humans a large number of variants have been identified but only a few in animals and none are deleterious. The identified ones are the three adult hemoglobin types, HbA, HbB and HbC. There is also an embryonic, HbE, and a fetal hemoglobin, HbF.