METABOLISM AND TRANSPORT IN ANIMALS 



537 



Larynx 



Left bronchus 



Alveolar duct 

 Alveolus 



Bronchiole 

 Parietal pleura- 

 Visceral pleura 

 Connective tissue 



Left lung intact 



Pleural cavity 



Diaphragm 



Figure 389. The lungs of man, each enclosed in a double-walled sac which is composed of 

 visceral pleura and parietal pleura. The right lung is cut open to show the internal structure. 



will die unless pure oxygen is supplied 

 under pressure. The higher the altitude, the 

 lower the temperature required to boil fluids. 

 Hence, at approximately 63,000 feet, the 

 pressure is so reduced that the body fluids, 

 including the blood, literally boil. 



It is obvious that the reduced atmospheric 

 pressure of high altitudes requires a pressure 

 cabin if one were to survive in space. Pilots 

 flying jet planes above 48,000 feet must 

 wear pressurized suits. 



By taking advantage of what is known 

 about aviation physiology, it has been possi- 

 ble for man to attain an altitude of about 

 24 miles above the earth. At such a height, 

 one is so near the top of the ocean of at- 

 mosphere that less than 1 per cent is above 

 him. Nevertheless, mice sent into outer 

 space have returned alive in a pressurized 

 rocket which reached a height of 36 miles. 

 To conquer outer space, a thorough under- 

 standing of the physiolog}' of respiration and 

 circulatory functions is needed to provide 

 the necessary safeguards. 



When man moves into outer space, he 



enters a hostile environment, one for which 

 he is not biologically adapted. Yet, there is 

 serious interest in flight to the moon. At 

 this writing men are being screened and 

 tested in equipment that it is hoped will 

 keep them alive in outer space. 



EXCRETORY SYSTEMS AND 

 DISPOSAL OF WASTES 



Continuitv of chemical reactions in cells 

 depends on the removal of the waste prod- 

 ucts of their metabolic activity. The con- 

 tinual removal of metabolic wastes or excre- 

 tions is necessary. A metabolic waste is 

 known as an excretion; also the removal of 

 metabolic wastes from the body is called 

 excretion. Carbon dioxide is a waste product 

 of metabolism, but it has already been dealt 

 with in our discussion of respiration. As a 

 result of metabolism, the cell needs to get 

 rid of (1) certain soluble nitrogenous salts 

 such as urea, (2) soluble inorganic salts such 

 as sodium chloride, and (3) water, which is 



