308 ANATOMY. FOR NURSES [Chap. X\ 1 



phates and water, which result from the process of neutralization. 

 (See page 8.) 



(4) The conversion of glucose into glycogen, and the reconver- 

 sion of glycogen into glucose. 



(5) The conversion of glucose into fat. This is a chemical 

 change that is not well understood, but various experiments have 

 satisfied physiologists that the tissues can produce fat from supar. 



These changes can be classified under two heads: (1) anab- 

 olism, or the building-up processes, and (2) katabolism, or the 

 splitting of complex substances into simpler ones. 



Functions of metabolism. — Metabolic changes serve two im- 

 portant purposes: (1) the repair and growth of tissue, and 



(2) the release of chemical energy in the form of heat, nervous 

 activity, and muscular activity. 



Factors which promote metabolic changes. — The factors which 

 produce metabolic changes are: (1) enzjTnes, (2) oxj'gen, and 



(3) internal secretions. It was formerly taught tliat the oxA'gen 

 absorbed from the lungs was responsible for all the processes of 

 oxidation that occur in the body. More accurate study has dem- 

 onstrated that while oxj'gen is an important factor, it is only one, 

 and the enzymes that are present in nearly all the body tissues 

 are capable of decomposing complex materials into simpler sub- 

 stances. Moreover, it is generally considered that the action 

 of the tissue enzymes comes first and causes decomposition by 

 hydrolysis, then other enz^^Tnes termed oxidases activate the pro- 

 cess of oxidation. 



METABOLISIM OF FATS 



We have traced the digested fat or chyle into the lacteals. 

 From the small lacteals it must find its way through the larger 

 lymphatics in the mesentery to the thoracic duct, and then 

 through the thoracic duct to the blood. This fat is carried by the 

 blood to all the different parts of the body, and the tissues slowly 

 take it out as they need it in their metabolic processes. Within 

 the tissues it serves as a fuel and is oxidized to supply the energy 

 needs of the cells. If fat is burned outside the body, heat is lib- 

 erated, and the waste products are carbon dioxide and water. 

 This process is similar to the one that takes place in the body. 

 Fat that is not required for the production of energy is stored up 

 in certain parts of the body, but not all the adipose tissue found in 



