MCH


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hemoglobin

 [he´mo-glo″bin]
the main functional constituent of the red blood cell, serving as the oxygen-carrying protein; it is a type of hemoprotein in which each molecule is a tetramer composed of four monomers held together by weak bonds. It consists of two pairs of polypeptide chains, the globins, each having an attached heme molecule composed of iron plus a protoporphyrin molecule. Symbol Hb.
Chemistry and Physiology.
The iron atom has a free valence and can bind one molecule of oxygen. Thus, each hemoglobin molecule can bind one molecule of oxygen. The binding of oxygen by one monomer increases the affinity for oxygen of the others in the tetramer. This makes hemoglobin a more efficient transport protein than a monomeric protein such as myoglobin. 

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 per cent saturated with oxygen. Venous blood is darker because it is only about 20 to 70 per cent 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 120-day life span of a red blood 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 can result, with high methemoglobin levels causing dyspnea and cyanosis.

A secondary function of hemoglobin is as part of the blood buffer system. The histidine residues in the globin chains act as weak bases to minimize the change in blood pH that occurs as oxygen is absorbed and carbon dioxide released in the lungs and as oxygen is delivered and carbon dioxide taken up from the tissues.

As erythrocytes 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.

The hemoglobin concentration of blood varies with the hematocrit. The normal values for the blood hemoglobin concentration are 13.5 to 18.0 g/100 ml in males and 12.0 to 16.0 g/100 ml in females. The normal mean corpuscular hemoglobin concentration, which is the concentration within the red blood cells, is 32 to 36 g/100 ml.
Variant and Abnormal Hemoglobins. There are six different types of globin chains, designated by the Greek letters α, β, γ, δ, ε, and ζ. The composition of a hemoglobin is specified by a formula such as α2β2, which indicates a tetramer containing two α chains and two β chains. The chains are coded by different genes, which are turned on and off during development in order to produce hemoglobins with the oxygen-carrying properties required at each developmental stage. In the first three months of embryonic development, when blood cells are produced in the yolk sac, embryonic hemoglobins such as Hb Gower (α2Aε2) or Hb Portland (ζ2γ2) are produced. As erythropoiesis shifts to the liver and spleen, the fetal hemoglobin Hb F (α2γ2) appears. When erythropoiesis shifts to the bone marrow during the first year of life, the adult hemoglobins Hb A (α2β2) and Hb A22δ2) begin to be produced.

Many abnormal hemoglobins arising from mutations have been discovered. Some have altered oxygen affinity, some are unstable, and in some the iron atom is oxidized, resulting in congenital methemoglobinemia. Some mutations result in a reduced rate of hemoglobin synthesis. All such conditions are known as hemoglobinopathies.

The most common hemoglobinopathy is sickle cell disease, caused by a mutation replacing the sixth amino acid in the β chain, normally glutamic acid, by valine. The variant hemoglobin α2βS2 is known as Hb S. Mutations resulting in reduced synthesis of one of the chains are called thalassemias. They can result from deletion of the gene for a chain or from a mutation in the regulatory gene that controls the synthesis of the chain.
The life cycle of red blood cells and the breakdown of hemoglobin. From Polaski and Tatro, 1996.
hemoglobin A1c hemoglobin A with a glucose group attached to the amino terminal of the beta chain; it is made at a slow constant rate during the 120-day life span of the erythrocyte. It accounts for 3 to 6 per cent of the total hemoglobin in a normal person and up to 12 per cent in persons with diabetes mellitus. Increased levels correlate with glucose intolerance in diabetics; with good diabetic control its level returns to normal range, so that periodic assays can be helpful in evaluating effective control of diabetes.
glycated hemoglobin (glycosylated hemoglobin) any of various hemoglobins with glucose attached nonenzymatically; the most common one is hemoglobin A1c. The percentage of hemoglobin that is glycosylated can be assessed over a long period of time as a gauge of blood sugar control; the normal range for a nondiabetic person is between 4 and 6 per cent.
mean corpuscular hemoglobin (MCH) the average hemoglobin content of an erythrocyte, conventionally expressed in picograms per red cell, obtained by multiplying the blood hemoglobin concentration (in g/dl) by 10 and dividing by the red cell count (in millions per ml): MCH = Hb/RBC.

MCH

Abbreviation for mean corpuscular hemoglobin.

MCH

mean corpuscular hemoglobin.

MCH

2 abbreviation for mean corpuscular hemoglobin.

MCH

Abbreviation for:
maternal and child health
mean corpuscular haemoglobin
melanin-concentrating hormone
methacholine
methylcyclohexanol
muscle contraction headache (tension headache, see there)

MCH

1. Maternal and Child Health.
2. Mean corpuscular hemoglobin A measurement of the Hb per individual erythrocyte Ref range 26-34 pg/red cell–SI.

MCH

Abbreviation for mean corpuscular hemoglobin.

Mch

Abbrev. for Master of Surgery.

Mean corpuscular hemoglobin (MCH)

A measurement of the average weight of hemoglobin in a red blood cell.

MCH

Abbreviation for mean corpuscular hemoglobin.

MCH,

MCH

mean corpuscular hemoglobin, an expression of the average hemoglobin content of a single cell in picograms, obtained by multiplying the hemoglobin in grams by 10 and dividing by the number of erythrocytes (in millions).
References in periodicals archive ?
The researchers also observed that test mice conditioned to develop cocaine cravings had increased amounts of MCH and dopamine in their nucleus accumbens.
Nationwide, nearly three in four pregnant women served by the MCH program have some source of third-party coverage, generally through Medicaid.
Unlike well-baby nurseries and NICU's, MCH clinics have not yet been investigated as a hearing screening context (Kennedy, Kimm, Cafarelli-Dees, Campbell & Thornton, 1998:1963).
The two analytes that entered the logistic regression model, using the stepwise selection procedure, were MCH and HbBarts.
In addition, Congress took advantage of the consolidation to substantially reduce funding for the new MCH block grant.
About the Multicultural Health National The MCH National conference is an opportunity for marketers, healthcare providers, media companies, government officials, policy makers and representatives from health companies to network and learn about industry trends, best practices and emerging policy.
The Stable Outlook reflects Fitch's expectation that MCH will continue to generate solid operating results in spite of weaker occupancy.
The MCH system has been losing ground and an increasing burden of health expenditure has fallen on pregnant women and local government.
Given its market position, MCH has an extensive medical staff (over 600) that represents numerous pediatric subspecialties and also has the largest pediatric residency program in the southeastern U.
Cynthia comes to MCH from Adirondack Health, a $90M network of rural facilities where, as Chief Operating Officer, she is responsible for leading all clinical inpatient and outpatient ancillary support services.
The role of MCH and family planning services in HIV/AIDS control: is integration the answer?