PROBLEM 4. Hoiv the Cells Are Provided with Oxygen 



/^/^\ Larynx (voice box) Air sacs in section 



Trachea 

 (windpipe) 



Outer surface 

 of left lung 



227 



Bronchial tube 

 Air sacs 



Small artery 



Small vein 



Pleura 



Capillary network 

 in v/alls of air sacs 



Fig. 226 The right lung has been cut to show 

 the larger bronchial tubes. See Figure 221 for 

 the smallest bronchial tubes and the air sacs. 



Ciliated 



Fig. 227 A piece of lung highly magnified. 

 There are capillaries in the walls of all the air 

 sacs. Of what iniportavce is this? 



epithelial cell 



Fig. 228 Mucous inembrane 

 lining the breathing pas- 

 sages. It contains two very 

 differeTit kinds of cells. How 

 does each help in cleansing 

 the air that enters? 



Secretion 



Mucous (gob/ef) cell 



Cell body 



Nucleus 



voice box (larynx — \2.r'\r\ks) it enters 

 the windpipe (also called trachea — tray'- 

 kee-a). This tube, about one-half inch 

 across, extends down a little more than 

 four inches in an adult of average size. 

 Then it divides into left and right 

 branches (bronchi — bron'ky). Each 

 branch enters a lung and divides and 

 subdivides like the branches of a tree. 



The windpipe is lined with epithelial 

 cells which have cilia lashing upwards. 

 In its walls lie incomplete hoops of carti- 

 lage which keep the windpipe open, al- 

 lowing free passage of air. They support 

 and protect the tube. The branches also 

 have cartilage support but the amount of 

 cartilage gets less and less as the branches 

 become smaller. The finest branches lack 



