E-content for hemoglobin
Assignments
1. Determine haemoglobin based on estimation of oxygen or carbon monoxide capacity or iron content.
2. Study the detailed structure of haemoglobin and related diseases
FAQs
1. Write a note on Haemoglobin
Hemoglobin (Hb) is an erythrocyte protein complex comprised of two sets of identical pairs of subunits, each of which bind an iron-prophyrin group commonly called heme. Generally containing two alpha or alpha-like globulin chains, the remaining subunits may be beta, gamma, delta or epsilon, or in the case of infants, fetal hemoglobin that is replaced during the first year of life.
2. Explain mechanism for haemoglobin action?
Haemoglobin carries oxygen from places of high oxygen pressure (lung) to places of low oxygen pressure (tissues), where it readily releases the oxygen. Haemoglobin also returns CO2 from the tissues to the lungs. Heme group of haemoglobin binds and releases oxygen or carbon dioxide in response to slight changes in local gas tension. Free oxygen or carbon dioxide bound by one heme group facilitates subsequent binding by the other heme groups in a given hemoglobin molecule. Subtle changes in pH also regulate hemoglobin affinity for free gases, resulting in a high level of hemostatic control.
3. What is hemoglobin complexes, mention some of them.
Hemoglobin can combine with other substances besides oxygen, some normally and some abnormally. Some of these commonly encountered complexes are carbaminohemoglobin, carboxyhemoglobin, methemoglobin, sulfhemoglobin, and cyanmethemoglobin.
4. Add a note on carboxyhemoglobin.
When hemoglobins combine with carbon monoxide (CO), carboxyhemoglobin is formed. Hemoglobin has a much greater affinity for CO than for oxygen. Therefore, it readily combines with CO even when CO is present in low concentrations. Fortunately the formation of carboxyhemoglobin is reversible, so, once CO is removed from the blood, the hemoglobin combines with oxygen.
5. Write a short note on methemoglobin. Methemoglobin is an abnormal Hb in which iron is oxidized from its ferrous to ferric state. Therefore, it is incapable of carrying oxygen. Normally it is present in low concentrations, but its formation increases in the presence of certain chemicals or drugs. The formation of methemoglobin is reversible.
6. Describe briefly sulfhemoglobin.
This is an abnormal Hb complex formed by the action of some drugs and chemicals such as sulfonamides. Once it is formed, it is irreversible and remains in the carrier RBC. It is incapable of transporting oxygen.
7. Explain cyanmethemoglobin (hemoglobin-cyanide).
This is formed by the action of a chemical called cyanide (for example. Potassium cyanide, KCN). The combination is reversible. Hemiglobincyanide is the methemoglobin bonded to cyanide ions.
8. Why cyanmethemoglobin method is the most accurate method.
To measure accurately the total Hb in the blood, it is essential to prepare a stable derivative that will contain all the a Hb forms (complexes) that are present in the blood. All forms of circulating hemoglobin are readily converted to hemoglobin-cyanide (cyanmethemoglobin), except for sulfhemoglobin which is normally not present in the blood. Therefore, the cyanmethemoglobin method is the most accurate method for the determination of hemoglobin. 9. Write a note on discovery of cyanmethemoglobin method.
The original cyanmethemoglobin technique was proposed by Stadie in 1920. This method used separated alkaline ferricyanide and cyanide reagents. A single reagent was introduced by Drabkin and Austin in 1935. In 1958 the National Research Council (NRC) recommended adoption of the cyanmethemoglobin procedure based on field trials conducted by the Army Medical Department. In 1966 the International Committee on Standardization in Hematology approved the proposal that all clinical laboratories should adopt this method exclusively.
10. Explain in detailed the principle of cyanmethemoglobin method.
Whole blood is diluted in cyanmethemoglobin reagent. This reagent hemolyzes the erythrocytes which releases hemoglobin into the solution. The ferrous ions (Fe2+) of the hemoglobin molecules are oxidized by potassium ferricyanide to ferric ions (Fe3+). This oxidation results in the formation of methemoglobin. Methemoglobin combines with the cyanide ions (CN-) to form cyanmethemoglobin, a stable compound. When measured spectrophotometrically at 540 nm, the absorbance of cyanmethemoglobin follows Lambert-Beer's law and is directly proportional to the concentration of hemoglobin in the blood. A reference (standard) curve is prepared using cyanmethemoglobin standard solutions of known hemoglobin concentrations. An unknown hemoglobin concentration may be calculated from the measured absorbance, read from a standard calibration curve, or read directly from the instrument scale of specialized instruments. The color intensity measured at 540 nm is proportional to the total hemoglobin concentration.
11. Mention normal hemoglobin (Hb) values.
Normal Hb values are
Adults
Males-13.0 – 18.0 g/dl
Females-11.0 – 16.0 g/dl
Children
At birth=13.6 – 19.6 g/dl
At one year=11.3 – 13.0 g/dl
10 – 12 years=11.5 – 14.8 g/dl
12. Mention the significance of hemoglobin measurement.
Measurements of hemoglobin values are associated with a variety of conditions ranging from anemias (low Hgb), erythrocytosis (high Hgb), thalassemias (aberrant chain synthesis), and sickling disorders (abnormal complex shape). Anaemia is the most common nutritional deficiency in India. It cannot be diagnosed clinically as the symptoms and signs are not sensitive or specific. Diagnosis of anaemia is made on the basis of Hb estimation. Objectives
Upon completion of this practical, students should be able to: To understand brief composition of hemoglobin To Learn different types of haemoglobin complexes To know discovery of cyanmethemoglobin method To learn principle behind cyanmethemoglobin method To study practical demonstration for colorimetric determination of haemoglobin To know significance and normal values of hemoglobin
MCQs
1. Hemoglobin (Hb) is an erythrocyte protein complex comprised of
2 alpha and 2 beta chains 1 alpha and 1 beta chains 2 alpha and 1 beta chains 1 alpha and 2 beta chains
2. Haemoglobin contain
Fe++ Cu++ Mg++ None of the above
3. Heme binds and releases oxygen or carbon dioxide in response to slight changes in
Concentration of oxygen local gas tension none of the above Both A and B
4. Which haemoglobin complex is irreversible
Carboxyhemoglobin
Methemoglobin
Sulfhemoglobin cyanmethemoglobin.
5. When hemoglobins combine with carbon monoxide (CO) Carboxyhemoglobin Methemoglobin Sulfhemoglobin cyanmethemoglobin.
6. Which is an abnormal Hb in which iron is oxidized from its ferrous to ferric state Carboxyhemoglobin Methemoglobin Sulfhemoglobin cyanmethemoglobin.
7. This is an abnormal Hb complex formed by the action of some drugs and chemicals
Carboxyhemoglobin Methemoglobin Sulfhemoglobin cyanmethemoglobin.
8. This haemoglobin complex is formed by the action of a chemical called cyanide
Carboxyhemoglobin Methemoglobin Sulfhemoglobin cyanmethemoglobin.
9. All forms of circulating hemoglobin are readily converted to hemoglobin- cyanide (cyanmethemoglobin), except for ------which is normally not present in the blood.
Carboxyhemoglobin Methemoglobin Sulfhemoglobin cyanmethemoglobin.
10. Which method is the most accurate method for the determination of hemoglobin.
Carboxyhemoglobin Methemoglobin Sulfhemoglobin cyanmethemoglobin.
Glossary
Absorbance- A measure of the capacity of a substance to absorb light of a specified wavelength. It is equal to the logarithm of the reciprocal of the transmittance.
Anemia – A condition in which there is a deficiency of red cells or of haemoglobin in the blood, resulting in pallor and weariness.
Hematology-The branch of medicine involving study and treatment of the blood.
Irreversible- Not able to be undone or altered Oxidation- The process or result of oxidizing or being oxidized.
Polycythemia- An abnormally increased concentration of haemoglobin in the blood, either through reduction of plasma volume or increase in red cell numbers. It may be a primary disease of unknown cause, or a secondary condition linked to respiratory or circulatory disorder or cancer.
Sickle cell anemia- A severe hereditary form of anaemia in which a mutated form of haemoglobin distorts the red blood cells into a crescent shape at low oxygen levels. It is commonest among those of African descent.
Thalassemia- Any of a group of hereditary haemolytic diseases caused by faulty haemoglobin synthesis, widespread in Mediterranean, African, and Asian countries.
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