BODY TISSUES 293 



and inorganic ions, and 67 per cent water. When the erythrocytes 

 are ruptured, or if the permeabiHty of the cell membranes is increased, 

 hemoglobin escapes and forms a homogeneous solution. Such blood 

 is said to be laked or hemolyzed. 



Erythrocytes are produced in the bone marrow and to a limited 

 extent in the spleen by a process called hemopoiesis. Nucleated 

 daughter cells are formed as buds on the large erythroblasts of the 

 bone marrow. After the cells are budded off they enter the general 

 circulation, gradually lose their nucleus, and accumulate hemoglobin. 

 The non-nucleated erythrocytes do not have a long life, estimates of 

 the average life span varying from 20 days to 125 days. Continuous 

 disintegration of aged erythrocytes occurs in the blood vessel walls 

 of the liver, giving rise to the bile pigments (page 470). 



The primary function of the erythrocytes is the transference of 

 oxygen from the limgs to rapidly metabolizing tissues. Hemoglobin is 

 the component of the red cell that is directly involved in this transfer. 



Hemoglobin is a conjugated protein consisting of the iron-contain- 

 ing pigment heme and the protein globin, a member of the histone 

 (page 114) class. The hemoglobin content of normal human blood 

 averages about 15.8 g./lOO ml. in the male and 13.8 g./lOO ml. in the 

 female. The hemoglobin content of the blood decreases after blood 

 losses from wounds or from impairment of the synthetic sites by 

 chemical poisoning, or by abnormal destruction of red cells, as in 

 spleen and liver misfunction. Anemias also develop as a result of 

 diets deficient in vitamins, iron, or copper. 



When the protein globin is removed, the iron-containing heme 

 remains. Heme is an iron derivative of protoporphyrin, an intensely 

 colored compound containing the porphyrin ring system (page 470). 

 The iron in reduced hemoglobin is in the ferrous state. In oxygenated 

 hemoglobin it is still in the ferrous state; the oxygen is assumed to be 

 loosely linked to the iron by a residual valence force. Four molecules 

 of heme tmitc ^vith 1 globin to form hemoglobin as shown below. 



heme heme 



\ . / 

 globin 



heme heme 



The linkages involve the ferrous ions of heme and histidyl components 

 of the globin moiety. Experiments have shown that each molecule 

 of hemoglobin is capable of transporting 4 molecules of oxygen. 



(heme)4globin + 4O2 ^ (heme 02)4globin 



