92 



GENERAL CONCEPTS 



100 -- 



75 



Per cent 

 of 



Ham.ocy.anin „ 

 Oxygenated 



25-- 



50 100 



Oxygen tension (pOJ in mm. Hg 



Figure 5.5. The effect of carbon dioxide tension (pCOa) on the delivery of oxygen 

 to tissues. The dotted line A indicates the amount of oxygen delivered as the pOo falls 

 from that of arterial blood to that of venous blood. The dotted line B indicates the extra 

 amount of oxygen delivered because the pC02 increases at the same time. 



involved marked changes not only in the morphology of the respiratory 

 organs, but also in the chemical properties of the heme proteins serving 

 as blood pigment. 



29. The Elimination of Wastes Other than Carbon Dioxide 



In the course of the metabolic processes by which cells utilize sub- 

 stances for energy and for growth and maintenance of the protoplasm, 

 wastes are produced which must be removed. The most important are 

 the nitrogenous wastes which result primarily from the deamination of 

 amino acids. These are of no further use to the animal and, being toxic, 

 would seriously interfere with metabolism if they accumulated. They 

 are removed from the blood and other body fluids of vertebrates by the 

 kidneys. The role of the vertebrate kidney, and of the excretory organs 

 of most other animals, is not limited to the elimination of nitrogenous 

 wastes, but includes the regulation of the volume of body fluids— i.e., 

 the water content of the body-and the regulation of the concentration 

 of salts, acids, bases and organic substances in the body fluids. The 

 cells of the body require a constant environment for their continued 

 normal functioning. The kidneys, by excreting certain substances and 

 conserving others, maintain the required constancy of the blood and 

 body fluids. The substances to be excreted are in solution, generally, 

 in the intracellular fluid, and the excretory process may involve simple 

 diffusion or active processes in which energy is expended. 



In most protozoa, the removal of wastes is accomplished by diffusion 

 through the cell membrane into the surrounding water where the con- 

 centration is lower. Protozoa living in fresh water have the additional 

 problem of ridding the body of the water which constantly enters the 



