The oxygen-carrying pigment that is present in red blood cells. Haemoglobin molecules, which are produced by bone marrow, are made up of 4 protein chains (2 alpha- and 2 betaglobin) and 4 haem (a red pigment that contains iron).
Oxygen from the lungs enters red blood cells in the bloodstream. The oxygen then combines chemically with the haem within the haemoglobin to form oxyhaemoglobin, which gives blood in the arteries its distinctive bright red colour and is carried around the body. In areas that need oxygen, the oxyhaemoglobin releases its oxygen and reverts to haemoglobin, giving blood in the veins its distinctive darker colour.Some defects in haemoglobin production result from a genetic disorder; such defects are subdivided into errors of haem production, known as porphyrias, and those of globin production, known as haemoglobinopathies. Other defects, such as some types of anaemia, have a nongenetic cause.
The colouring compound which produces the red colour of blood. Haemoglobin is a chromoprotein, made up of a protein called globin and the iron-containing pigment, haemin. When separated from the red blood corpuscles – each of which contains about 600 million haemoglobin molecules – it is crystalline in form.
Haemoglobin exists in two forms: simple haemoglobin, found in venous blood; and oxy-haemoglobin, which is a loose compound with oxygen, found in arterial blood after the blood has come into contact with the air in the lungs. This oxyhaemoglobin is again broken down as the blood passes through the tissues, which take up the oxygen for their own use. This is the main function of haemoglobin: to act as a carrier of oxygen from the lungs to all the tissues of the body. When the haemoglobin leaves the lungs, it is 97 per cent saturated with oxygen; when it comes back to the lungs in the venous blood, it is 70 per cent saturated. The oxygen content of 100 millilitres of blood leaving the lungs is 19·5 millilitres, and that of venous blood returning to the lungs, 14·5 millilitres. Thus, each 100 millilitres of blood delivers 5 millilitres of oxygen to the tissues of the body. Human male blood contains 13–18 grams of haemoglobin per 100 millilitres; in women, there are 12–16 grams per 100 millilitres. A man weighing 70 kilograms (154 pounds) has around 770 grams of haemoglobin circulating in his red blood corpuscles.
n. a substance contained within the red blood cells (*erythrocytes) and responsible for their colour, composed of the pigment haem (an iron-containing *porphyrin) linked to the protein globin. Haemoglobin has the unique property of combining reversibly with oxygen and is the medium by which oxygen is transported within the body. It takes up oxygen as blood passes through the lungs and releases it as blood passes through the tissues. Blood normally contains 115 to 180 g/l of haemoglobin. See also myoglobin; oxyhaemoglobin.
A1c see glycated haemoglobin.
The presence of blood pigment in the URINE caused by the destruction of blood corpuscles in the blood vessels or in the urinary passages. It turns urine a dark red or brown colour. In some people this condition, known as intermittent haemoglobinuria, occurs from time to time, especially on exposure to cold. It is also produced by various poisonous substances taken in the food. It occurs in malarious districts in the form of one of the most fatal forms of MALARIA: BLACKWATER FEVER. (See also MARCH HAEMOGLOBINURIA.)... haemoglobinuria
A form of haemoglobin that is bound to the sugar glucose. In most people, 3–8 per cent of haemoglobin is glycosylated. In people with diabetes mellitus, the level of glycosylated haemoglobin may be raised if treatment has not kept the blood glucose level within the normal range. Glycosylated haemoglobin levels indicate blood glucose levels over the preceding 3 months.... glycosylated haemoglobin
This forms a small proportion of the total HAEMOGLOBIN in the blood. It di?ers from the major component, HbA, in that it has a glucose group attached. The rate of synthesis of HbA1c is a function of the blood-glucose concentration, and since it accumulates throughout the life span of the red blood cell – normally 120 days – the concentration of HbA1c is related to the mean blood-glucose concentration over the past 3–4 months. It is thus a useful indicator of medium-term diabetic control (see DIABETES MELLITUS) – a good target range would be a concentration of 5–8 per cent. When interpreting the HbA1c level, however, it is important to remember that wide ?uctuations in blood-glucose concentration, together with ANAEMIA or a reduced ERYTHROCYTES life span, may give misleading results.... glycosylated haemoglobin (hba1c)
Abnormal HAEMOGLOBIN formation occurs in the haemoglobinopathies, which are hereditary haemolytic anaemias, genetically determined and related to race. The haemoglobin may be abnormal because: (1) there is a defect in the synthesis of normal adult haemoglobin as in THALASSAEMIA, when there may be an absence of one or both of the polypeptide chains characteristic of normal adult haemoglobin; or (2) there is an abnormal form of haemoglobin such as haemoglobin S which results in sickle-cell disease (see ANAEMIA). This abnormality may involve as little as one amino acid of the 300 in the haemoglobin molecule. In sickle-cell haemoglobin, one single amino-acid molecule – that of glutamic acid – is replaced by another – that of valine; this results in such a de?cient end product that the ensuing disease is frequently severe.... haemoglobinopathies
A complication of walking and running over long distances. It is due to damage to red blood cells in the blood vessels of the soles of the feet. This results in HAEMOGLOBIN being released into the bloodstream, which is then voided in the URINE – the condition known as HAEMOGLOBINURIA. No treatment is required.... march haemoglobinuria
(glycosylated haemoglobin) any derivative of haemoglobin in which a glucose molecule is attached to the haemoglobin molecule. The most abundant form of glycated haemoglobin is haemoglobin A1c (HbA1c), levels of which are significantly increased in diabetes. The percentage of the HbA molecules that become glycated is dependent on the general level of glucose in the plasma over the lifetime of the molecule (generally three months); this percentage is therefore used as the standard measure of the degree of control of *hyperglycaemia in a person with diabetes over this period. HbA1c values are now expressed in mmol per mol haemoglobin (mmol/mol) rather than as a percentage. The use of HbA1c as a screening tool for diabetes mellitus has become recognized.... glycated haemoglobin
(PNH) a type of acquired haemolytic *anaemia that results from an abnormality of the red blood cell membrane. It is due to a defect in the formation of glycosylphosphatidylinositol (GPI), whose role is to anchor proteins to the lipid framework of the membrane. This leads to increased *complement-mediated destruction of red blood cells, which results in the release of haemoglobin in the circulation and then in the urine, giving the latter a reddish colour. Some patients may develop blood clots.... paroxysmal nocturnal haemoglobinuria
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