336 



THE VERTEBRATE BODY 



The human respiratory system shows several important differences 

 when compared with that of the frog. Because our skin is so thick and 

 dry, we cannot absorb oxygen through our skin. However, the human 

 body has a much higher rate of metabolism and in consequence needs a 

 much larger supply of oxygen. This extra oxygen is supplied by a 

 more highly developed system of alveoli within the lungs which gives 

 a much greater surface exposed to the air in proportion to size than the 

 less complex lungs of the frog. 



Larynx 



Bronchial 

 tube 



Lungs 



Fig. 23.6. Diagram of the lower respiratory tract of man. 



Within our larynx, as in the frog, there are vocal cords. We have 

 a trachea, or windpipe, leading from the larynx. The frog has no 

 trachea. Our trachea is supported by C-shaped cartilage rings which 

 prevent it from collapsing when we inhale. At the posterior end the 

 trachea branches into a pair of bronchi which extend out to the lungs 



