PROBLEM 4 How Are All Our Cells Provided xvith a 



Constcint Supply of Oxygen? 



Where oxygen enters the blood. 1 he Hv- 



irg, working cells need food. The food 

 enters the blood in the villi of the small 

 intestine and is carried to the cells. The 

 cells also need a constant supply of oxy- 

 gen; respiration goes on in all the cells. 

 Blood brings the oxygen to the cells. 

 Much oxygen is used and there are spe- 

 cial organs that make it possible for large 

 amounts of oxygen from the surrounding 

 atmosphere to enter the blood. These 



Brain case 

 Sinus cavities 



Opening of 

 tube from ear 



Adenoid 



oryans aie the lungrs. The lun""s are so 

 placed and constructed that an enormous 

 amount of blood comes near a very large 

 quantity of air in a short time. 



Passageways to the lungs. If you do Ex- 

 ercise I and study Figure 225 you will 

 be able to trace air along the air passage- 

 ways in the head and neck. By doing 

 Exercise 2 you will learn how the air is 

 cleansed and warmed on the way to the 

 lungs. Once it has passed through the 



Fig. 225 Section through head and 

 neck. Name in order all the passages 

 throtigh which the air passes in trav- 

 elling to the windpipe. What hap- 

 pens to air as it is breathed in 

 through the head and neck? 



Mouth cavity 



Tongue 

 Left Tonsil 

 Epiglottis 



Voice box {larynx.) 



Spinal cord 



Food pipe 

 (oesopfiogus) 



Back bone 

 Windpipe (trachea) 



Nose cavity 

 Throat 

 Left vocal cord 



Thyroid gland 



