GENERAL ZOOLOGY 



ALL CELLS 



»• Carbohydrate 



»- Lipid 



KIDNEY 



Fig. 3.24. Schema showing dynamic quality of protein metabolism in mammals. In the con- 

 tinuous metabolic turnover, proteins from the diet or from any one tissue can contribute to the 

 protein of any other tissue or be degraded. 



tenance of body temperature. It also plays a protective role as filling or pack- 

 ing material about and between organs. 



Some of the fatty acids and glycerol are absorbed into the blood and pass to 

 the liver capillaries. The liver is not normally a fat depot. Instead, the 

 important function of the liver in fat metabolism is the synthesis of phospho- 

 lipids which are returned to the blood to be used by all cells. Glycerol can 

 be converted to glucose. 



Unlike the hexoses and lipids, the amino acids absorbed into the blood are 

 not stored (Fig. 3.24). They are removed by all cells in connection with the 

 synthesis of protein for maintenance and growth. Excess amino acids can be 

 converted to glucose and then to fat and stored; this is an irreversible reaction. 

 Amino acids can also be converted to glucose and be used as fuel for the cell. 

 During their conversion to glucose the amino acids are deaminated; that is, 



78 



