Prof. J.P.N. Mishra
There are an estimated 200 to 300 million molecules of haemoglobin in each RBC, which make an about 95 % of the dry weight of each cell. Each haemoglobin molecule is composed of four protein chains (Fig 1- 3). Each chain called a globin, is bounded to a red pigment, as a heme molecule. Each heme molecule contains an iron atom. Therefore one haemoglobin molecule contains four iron atoms. This structural fact enables one haemoglobin molecule to unite with four oxygen molecules to form oxyhemoglobin (a reversible reaction). Haemoglobin can also combine with carbon dioxide to form carbaminohemoglobin (also reversible). But in this reaction the structure of globin part of the haemoglobin molecule, rather than its heme part, makes the reaction possible (Fig. 1-3).
Fig. 1-12. Life cycle of red blood cells.
Blood of a man usually contains more haemoglobin than that of a women. In normal men, 100 ml of blood contains 12 to 16 gm of haemoglobin. The normal haemoglobin contents of women's blood is little less - specifically, in the range of 10 to 14 gm per 100 ml. This is due to Testosterone in the male that tends to stimulate erythrocyte production and cause an increase in RBC numbers. Increased level of haemoglobin in males is directly related to increased erythrocyte number.
Haemoglobin has multifaceted and significant functions. At one hand it carries oxygen and carbon dioxide and at other hand it constitutes important buffers of blood to maintain acid-base balance. It also mediates formation of numerous pigments of bile, stool, urine etc. These functions are among several constituents of metabolism, which is ultimately responsible for normal healthy state (Chaudhuri, 2001).
