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HAEMOGLOBIN Normal iron metabolism: The primary function of the RBC is oxygen and CO2 transport. In order to achieve this function, they contain the specialized protein, HAEMOGLOBIN. Each red cell contains approximately 640 million haemoglobin molecules. Each haemoglobin molecule is composed of Iron (Haem) and globin (protein portion). Each globin part consists of four polypeptide chains ά 2 ß 2. The normal adult contains three types of haemoglobin: Hb A, Hb F and Hb A2. Iron is absorbed by duodenum and jejunim Average total body iron content 3500-4000 mg. Approximately 2/3 found in hemoglobin, Iron is also stored in RE cells (BM, Spleen and liver) as hemosiderin and ferratin. Also iron found in myglobin and myeloperoxidase and in certain electron transfer. Iron is more stable in ferric state (Fe+++) than in ferrous state (Fe++). The main function of the RBCs is to carry O2 to the tissues and to return carbon dioxide to the lungs. Normal Haemoglobins in adult blood. Structure Normal (%) Hb A α2ß2 96-98 Hb F α2 γ2 0.5-0.8 5 Hb A2 α2 δ2 1.5-3.2 The major switch from fetal to adult haemoglobin occurs 3-6 months after birth. 65% of Hb is synthesized in the erythroblast and 35 % at the reticulocyte stage. Haem synthesis occurs largely in the mitochondria by a series of biochemical reactions commencing with the condensation of glycine and succinyle co-enzyme A under the action of the key ratelimiting enzyme Gamma aminolevulinic acid synthetase (ð ALA synthetase). Vitamin B6 is an essential cofactor in the reaction. Haemoglobin structure: The hemoglobin molecule is a tetramer composed of four globin chains, each of which contains a haem ring. Haem consists of a protoporphyrin ring into which a ferrous iron atom has been inserted. The initial reaction in the haem synthesis pathway is the combination of glycine and succinyl coenzyme A (CoA) to form 6 alpha -aminolevulinic acid (ALA), which is catalyzed by the enzyme aminolevulinic acid synthetase (ALA synthetase). Vitamin B6 is an essential cofactor in the reaction. The final step in the pathway is insertion of the ferrous iron atom into protoporphyrin. Defects in various enzymes in the haem synthesis pathway cause many diseases. Normal adult red cell values: Male Female. Haemoglobin (g/dl) 13.5-17.5 11.5-15.5 Haematocrite (PVC) % 40-52 36-48 Red cell count (x10 12/l) 4.5-6.5 3.9-5.6 Mean cell haemoglobin (MCH pg) 27-34 Mean cell volume (MCV fl) 80- 95 Mean cell haemoglobin concentration 30-35 (MCHC g/dl) Reticulocyte count % 0.5-2 Absolute Values (Red cell indices): PCV% x 10 -------------- 1- mean cell volume = 7 RBC count. 2- mean cell haemoglobin = Hb (g/dl) x 10 -----------------RBC count. 3- mean cell haemoglobin concentration = Hb (g/dl) x 100 ------------------RBC count. 8