THE METABOLIC MACHINERY OF ANIMALS 



;n7 



Respiratory System in Man 



Air passes from tjie nostrils through the shthke glottis into the 

 windpipe. This tube, called the trachea, the top of which may easily 

 be felt as the " Adam's apple " of the throat, is supported by a series of 

 cartilaginous rings complete in front but incomplete behind and divid- 

 ing into two hronchi. Within the lungs, the bronchi break up into a 

 great number of smaller 

 tubes, the hronckiolcs, which 

 divide somewhat like the 

 small branches of a tree 

 and arc lined with ciliated 

 epithelial cells. The re- 

 mainder of the tubes are 

 also lined with ciliated cells, 

 the cilia of which are con- 

 stantly in motion lashing 

 with a quick stroke toward 

 the outer end of the tube, 

 that is, toward the mouth. 

 Hence any foreign material 

 in the tubes will be ex- 

 pelled first by the action 

 of the cilia and then by 



pharynjc 



xtvulcc. 

 -epiglottis 



esophagits 



.bronchial tubes 

 orbr^chioles 



coughing or 



"clearing the 



The respiratory system of man. Note the 

 cartilagenoiis rinjjs supporting the ducts. 



throat." 



The bronchial tubes end, 

 as already noted, in very 

 minute air sacs called al- 

 veoli. Great numbers of these are present, thereby increasing the 

 respiratory surface tremendously. These tiny pouches have elastic 

 walls into which air is taken when we inspire or take a deep breath. 

 Around the walls of the pouches and separated by a xcry thin 

 membrane, are numerous capillaries from the pulmonary artery 

 which brings the blood from the right ventricle of the heart to the 

 lungs. Through the very thin walls of the air sacs a diffusion of gases 

 takes place, which results in the blood giving up carbon dioxide and 

 taking in oxygen. Consequently the blood becomes a brighter red, 

 due to formation of oxyhemoglobin by the combination of oxygen with 

 the hemoglobin in the red corpuscles. 



