Physiology
Basic Cellular
Haemoglobin A2 (HbA2) is made up of which of the following globin chains:
Answer:
Haemoglobin A2 (HbA2), a normal variant of adult haemoglobin, makes up about 1.5 - 3.5 % of total adult haemoglobin and consists of two α and two delta (δ) globin chains.Haemoglobin
Physiology / Basic Cellular / Blood and Blood Flow
Last Updated: 24th April 2019
Red blood cells contain the specialised protein haemoglobin which is responsible for carrying oxygen and carbon dioxide in the blood. Haemoglobin is composed of four polypeptide globin chains each with its own iron containing haem molecule.
Haemoglobin Synthesis
Haemoglobin synthesis occurs in immature red blood cells. Haem synthesis occurs largely in the mitochondria by a series of biochemical reactions commencing with the condensation of glycine and succinyl coenzyme A under the action of the key rate-limiting enzyme delta-aminolevulinic acid (ALA) synthase; ultimately protoporphyrin combines with iron in the ferrous (Fe2+) state to form haem. The globin chains are synthesised by ribosomes in the cytosol.
Haemoglobin Degradation
Red cells are destroyed by macrophages in the liver and spleen after ~ 120 days. The haem group is split from the haemoglobin and converted to biliverdin and then bilirubin. The iron is conserved and recycled to plasma via transferrin or stored in macrophages as ferritin and haemosiderin. An increased rate of haemoglobin breakdown results in excess bilirubin and jaundice.
Types of Haemoglobin
There are three types of haemoglobin in normal adult blood: haemoglobin A, A2 and F.
- Normal adult haemoglobin (HbA) makes up about 96 - 98 % of total adult haemoglobin, and consists of two alpha (α) and two beta (β) globin chains.
- Haemoglobin A2 (HbA2), a normal variant of adult haemoglobin, makes up about 1.5 - 3.5 % of total adult haemoglobin and consists of two α and two delta (δ) globin chains.
- Foetal haemoglobin (HbF) makes up about 0.5 - 0.8 % of total adult haemoglobin and consists of two α and two gamma (γ) globin chains.
| Hb | Structure | Normal adult % |
|---|---|---|
| HbA | α2β2 | 96 - 98% |
| HbA2 | α2δ2 | 1.5 - 3.5% |
| HbF | α2γ2 | 0.5-0.8% |
Foetal haemoglobin is the main Hb in the later two-thirds of foetal life and in the newborn until approximately 12 weeks of age. Foetal haemoglobin has a higher affinity for oxygen than adult haemoglobin.
![By OpenStax College [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons](https://primary-cdn.frcemsuccess.com/wp-content/uploads/2018/09/1904_Hemoglobin-1024x517.jpg)
Structure of Haemoglobin. (Image by OpenStax College [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons)
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
