PROBLEM 3. HouD Materials Are Moved to arid from Cells 



Right lung 

 Fig. 221 Circulation of blood 



from right vetitricle to left 

 auricle. Blood from the right 

 ventricle goes only to the 

 lungs. The black vessels are 

 arteries. Does the blood in 

 the shaded vessels contain 

 much or little oxygen? Are 

 the shaded vessels veins or 

 arteries? What happens to 

 the blood as it passes through 

 the capillaries of the lungs? 

 To which chamber does it 

 go from the lungs? 



219 



Left lung 



/ 



m^ 



The tube is extremely narrow and you 

 can look out through its walls. You are 

 now in a capillary with very thin, trans- 

 parent walls. Here the corpuscle on 

 which you are riding changes color. 

 Oxygen leaves the hemoglobin and dif- 

 fuses into the neighboring cells. The 

 plasma in which your corpuscle is float- 

 ing is also undergoing changes, for foods 

 are diffusing out of the capillary and the 

 wastes of oxidation from the neighbor- 

 ing cells are entering the capillary. But 

 you never stop for any of these changes 

 to take place. On you go, noticing soon 

 that you are again in a slightly wider 

 tube and you cannot look out any more. 

 You have left the capillary. You are in a 

 vein and you are travelling straight up- 

 hill. You soon notice that you are joined 

 again by corpuscles that had been down 

 to the right foot. Then you meet the 

 friends who had travelled through the 

 stomach, the intestines, and other organs 

 in the abdominal cavity. You are by this 

 time riding in a very wide tube. This 

 wide tube (called the inferior vena cava) 

 connects with the right auricle and you 

 soon find yourself dropped into the right 



Right 

 ventricle 



auricle. Examine Figure 220 to trace your 

 course and that of some of your friends. 

 Figures 220 and 221 are diagrams to 

 make clear the course of the blood. 



You are now back in the heart but not 

 where you started from. You are on the 

 right side; you started from the left. In 

 this right auricle occurs another reunion. 

 For a large vein {superior vena cava) is 

 bringing back your friends who had 

 travelled to the head and arms. Without 

 stopping you are forced by the heart 

 contraction into the right ventricle. You 

 will soon be on your way out of the 

 heart once more. Continue tracing your 

 route by studying Figure 221. You go 

 into an artery. This time it is the pul- 

 monary artery. Again there are branches 

 and the artery gets narrower. Soon you 

 find yourself for a second time in an ex- 

 tremely narrow, transparent tube, a capil- 

 lary. But this time you are in a capillary 

 in the lung. You would know that you 

 are in the lung for your corpuscle be- 

 comes bright red once more as oxygen 

 diffuses into your capillary and unites 

 with the hemoglobin in your corpuscle. 

 Carbon dioxide, carried both by the red 



