366 - Multicellular Animals, Especially Man 



K-Hb0 2 + H-HC0 3 , and HHC0 3 ;=>H,0 



4- C0 2 — to indicate the stabilization of the 

 2 carrier and the simultaneous freeing of 

 C0 2 for diffusion into the alveoli of the lung. 



At the tissues, however, another trigger is 

 provided by the coming in of C0 2 and the 

 concurrent formation of carbonic acid, 

 HHC0 3 . This provides extra H+ ion for 

 the conversion of K-HbCX. to the less stable 

 form, HHbO L ., which then liberates free 2 . 

 Simultaneously, however, C0 2 is bound as 

 bicarbonate. Thus we may write: C0 2 -\- 

 H 2 0^±HHC0 3 and H-HCO, + KHb0 2 

 5±KHC0 3 + HHb0 2 and H-Hb0 2? ^ 

 H-Hb + 2 — to indicate the whole series of 

 reactions. The net effect, however, is to bind 

 C0 2 and to liberate 2 at the proper mo- 

 ment. Meanwhile, however, the pH situation 

 is stabilized by rapid exchanges of the H + 

 ion. Truly the hemoglobin molecule has 

 been cunningly evolved to subserve the essen- 

 tial functions of respiration, both external 

 and internal. Moreover, a special enzyme, 

 carbonic anhydrase, has been evolved to 

 speed up, by a factor of some 1300, the 

 C0 2 + H 2 *£ H • HC0 3 reaction. 



In summary, the chemical reactions which 

 liberate COo from the bicarbonates are 

 coupled with the oxygenation of hemoglobin. 

 Just as the pouring in of C0 2 at the tissues 

 favors the liberation of 2 at the proper 

 time, so the coming in of 2 fosters the free- 

 ing of C0 2 at the lungs. Another main factor 

 in the decomposition of the bicarbonates in 

 the lungs, of course, is the reduction of the 

 C0 2 concentration as this gas escapes into 

 the avleolar spaces. Very small changes in 

 the concentration of the gases in the blood in 

 the different capillary regions act upon these 

 chemical equilibria and determine the bind- 

 ing or freeing of each gas at the proper time 

 and in the proper place. 



ASPHYXIA 



Any failure in the delivery of oxygen to 

 the tissues, or in the usage of oxygen by the 

 tissues, produces asphyxia in greater or lesser 



degree. Accordingly the causes of asphyxia 

 may reside in the lungs, in the circulatory 

 system, or in the tissue cells. 



Pulmonary asphyxia may result from a 

 blocking of the bronchial passages, by water, 

 as in drowning, or by an exudate of tissue 

 fluid, as in pneumonia. When air cannot 

 reach a large proportion of the alveoli, the 

 quantity of oxygen absorbed and distributed 

 by the blood is correspondingly restricted. 

 Giving the patient pure oxygen helps — by 

 augmenting the oxygen absorbed by the 

 functioning alveoli; and in drowning, of 

 course, an artificial ventilation of the lungs 

 should be used if the asphyxia has abolished 

 the normal respiratory movements. In asthma, 

 there is a spasmic contraction of the muscles 

 in the walls of the bronchi and bronchioles, 

 which narrows these passages so drastically 

 that they cannot conduct adequate air to the 

 lungs. 



Curtailment of the circulation — due to dis- 

 orders of the heart or blood vessels — like- 

 wise curtails the delivery of oxygen to the 

 tissues. Carbon monoxide (CO), however, acts 

 upon the circulation in a different way. Car- 

 bon monoxide, which is present in illuminat- 

 ing gas and in the exhaust fumes of gasoline 

 motors, acts by blocking the capacity of 

 hemoglobin to combine with oxygen. Hemo- 

 globin unites with CO much more readily 

 than with 2 ; and the resulting cherry-red 

 compound, HbCO, has no afnnitv for oxvgen. 

 In carbon monoxide asphyxia, therefore, the 

 victim does not "turn blue," but appears 

 "flushed" due to the color of carbon-monoxyl 

 hemoglobin. Resuscitation from CO asphyxia 

 may be effected by artificial respiration, using 

 an augmented oxygen supply — if available. 

 Free Hb begins to be restored as soon as CO 

 is removed from the alveolar air; and this 

 restoration occurs more readily when the 

 2 pressure of the alveolar air is increased. 

 In anemia, all the available hemoglobin may 

 be oxygenated, but the amount of hemo- 

 globin is so low that the blood does not carry 

 enough oxygen to the tissues. 



Respiratory poisons, such as cyanide, act 



