LECTUEE X 

 RESPIRATION 



Respiration is the process by which the tissues gain oxygen 

 and give off impurities. This process is controlled by the res- 

 piratory center, a group of nerve cells located in the medulla, 

 a portion of the brain. Fibers from these cells form part of the 

 tenth cranial (vagus) nerve to the lungs and respiratory 

 muscles. This respiratory nerve mechanism is stimulated by the 

 presence of C0 2 in the blood, or by lack of oxygen ; whereas, it 

 is inhibited (restrained) by oxygen and thus the needed rate 

 of respiration is maintained. Apparently, the plain simple pur- 

 pose of respiration is twofold: (1) to get oxygen into the blood 

 and various body tissues, and (2) to get carbonic gas (C0 2 ) 

 and various other organic impurities out of the blood and body 

 tissues. It is a common mistake to suppose that respiration is 

 confined to the lungs. A very important portion of the true 

 respiration occurs between the blood and individual tissue cells 

 apart from the lungs. 



Respiration includes oxidation and also elimination of waste 

 products. This involves a double series of exchanges, one series 

 occurring in the lungs and a reversed series occurring mainly 

 in the tissue cells. All tissues and even the blood, when func- 

 tioning, consume oxygen and form carbon dioxid. 



Continuous oxidation processes in the body result in contin- 

 uous production of carbonic acid gas, urea, water, and other 

 waste products. 



Stages. — There are four stages in the complete act of respi- 

 ration: (a) air comes into the lungs; (b) blood takes out part 

 of the oxygen; (c) tissues take part of the oxygen away from 

 the blood and give back to the blood carbonic gas and other ma- 

 terials in exchange ; and (d) the blood trades off its carbonic gas 

 and other materials to the air for oxygen. 



Oxygen is carried to the tissues by the blood, and waste prod- 

 ucts are washed away from the tissues by the same fluid. 



The blood cannot unite with sufficient oxygen or eliminate its 



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