HAEMOGLOBINHAEMOGLOBIN

The main function of the RBCs is to carry O2 to the tissues and to return carbon dioxide to the lungs. 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 Each haemoglobin molecule is composed of Iron (Haem) and globin composed of Iron (Haem) and globin (protein portion).(protein portion).

• Each globin part consists of four Each globin part consists of four polypeptide chains α2ß2.polypeptide chains α2ß2.

• The normal adult contains three types The normal adult contains three types of haemoglobin: Hb A, Hb F and Hb of haemoglobin: Hb A, Hb F and Hb A2.A2.

Normal Haemoglobins in adult blood.

Hb AHb FHb A2

Structureα2ß2 α2γ2 α2δ2

Normal %96-98 0.5-0.8 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 rate-limiting 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 gamma -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.

Absolute Values (Red cell indices):

PCV% x 10

Mean Cell Volume =--------------------

RBC count.

(MCV)

Mean Cell Haemoglobin = Hb (g/dl) x 10

RBC count

(MCH)

Mean Cell Haemoglobin Concentration =

Hbx 100

PCV (MCHC)

Red cell indices

•MCV (mean corpuscular volume)•The average volume of RBC

Hct= 10(fl)

RBC count (m/µL)e.g. Hct= 40%

RBC=5.0 (m /µL)MCV= 40/5.0 10 = 80 fl

NR= 80-96 fl

• MCH (mean corpuscular (or cell) hemoglobin)• The average content of Hb in average RBC. • It is directly proportional to the amount of Hb

and RBC size.

Hb

RBC count (m/µL)(m/µL) 10 (pg)MCH =

e.g. Hb = 14 g/dlRBC = 4 (m/µL)(m/µL)

MCH= 14/4 10 = 35 pg

NR= 27-32 pg

• MCHC (mean corpuscular hemoglobin concentration)• Express the average concentration of hemoglobin

per unit volume of RBC.• It defined as the ratio of the weight of hemoglobin

to volume of RBC.

Hb (g/dl)

Hct (%)

100 (%)MCHC=

e.g. Hb = 14 g/dlHct = 45 %

MCHC 14/45 100 = 31%

NR= 32-36%

Normal adult red cell valuesNormal adult red cell values::

MaleMale FemaleFemale

Haemoglobin (g/dl)Haemoglobin (g/dl)13.5-17.513.5-17.511.5-15.511.5-15.5

Haematocrite (PVC)Haematocrite (PVC)%40-52%40-5236-4836-48

Red cell count (x10 12/l)Red cell count (x10 12/l)4.5-6.54.5-6.53.9-5.63.9-5.6

Mean cell haemoglobin Mean cell haemoglobin (MCH pg)(MCH pg)

27-3427-34

Mean cell volume (MCV fl)Mean cell volume (MCV fl)8080 - -9595

Mean cell haemoglobin Mean cell haemoglobin concentration (MCHC g/dl)concentration (MCHC g/dl)

32-3632-36

Reticulocyte countReticulocyte count%0.5-2%0.5-2