190 METABOLISM 



fast as it is formed. The sulphur and phosphorus are given off by 

 the excretory organs, and the carbon, hydrogen, and oxygen com- 

 bine and are stored in the liver in the form of glycogen. This sub- 

 stance is then released as the body needs it. 



Metabolism of fats. Fats are absorbed as glycerol, fatty acids, 

 and soaps by the lacteals of the villi. In the absorption process, 

 they are reassembled as fats, probably by the epithelial cells in the 

 villi. The absorbed fats travel through the lymphatics to the 

 thoracic duct which empties them into the venous system just before 

 draining into the superior vena cava. In this way, they become a 

 part of the blood. These fats are not in the original form of the 

 fat ; they are made into a fat which is characteristic of the species 

 in which the metabolism is taking place. They are carried to the 

 cells, where they are burned as fuel which serves as a source of 

 energy for muscular work and other activities. The resulting 

 wastes, carbon dioxide and water, are eliminated by the organs of 

 excretion. Some fat is used to build fatty tissue and the extra fat 

 is then stored in the vacuoles of cells in the form of drops of oil. 



QUESTIONS 



1. Give a definition of metabolism. 



2. Classify the functions of the body into anabolic and katabolic 

 functions. 



3. Discuss the metabolism of sugar ; of protein ; of fat. 



SUPPLEMENTARY READINGS 



Burton-Opitz, Textbook of Physiology (W. B. Saunders Co.). 

 Howell, W. H., Textbook of Physiology (W. B. Saunders Co.). 

 Martin and Weymouth, Elements of Physiology (Lea & Febiger). 

 Mitchell, P. H., General Physiology (McGraw-Hill Book Co.). 



