CHAPTER VII 

 PHYSIOLOGY OF ORGANS 



The organization of the bodies of higher animals into organs and 

 systems obviously makes possible a degree of interrelationship of function 

 not found in the physiological processes of simpler organisms. 



Organ Physiology Rests Upon Cell Physiology. — The basis of organ 

 physiology is the physiology of the cell, for obviously the function of an 

 organ is, in a sense, the sum of the functions of its component cells. 

 The cells do not share equally, however, in determining the function of 

 the whole organ, for certain cells directly perform the service to which 

 the organ is devoted, while others are only accessory to the main function. 

 For example, in the stomach the functions of the cells of the mucous 

 layer are of far greater immediate importance than are the functions of 

 any other cells of that organ, although the other cells are indirectly in- 

 dispensable. The physiology of an organ is more, however, than the 

 functions of its cells, since in cooperating the cells modify the performance 

 of one another, and there results a function of the organ as a whole, 

 which rests upon the functions of its parts. In like manner, though an 

 organ has a recognizable function, that function cannot be isolated 

 from the functions of other organs, for few organs occur singly. Usu- 

 ally they form part of some system, and the functions of the system are 

 the functions of the organs of which it is composed, plus certain activities 

 which depend on the close mutual relations of the included organs. In 

 the account of these functions duplication of the descriptons of func- 

 tions which were necessary in connection with the account of the 

 morphology of organs in Chapter VI cannot be wholly avoided, and 

 reference should be made to that chapter for some of the facts of physi- 

 ology and for further details as to the structure of the organs and 

 systems involved. 



Digestion in Man. — In the mouth, food is broken up, during which 

 process the three pairs of salivary glands pour out their secretion (saliva) 

 which is mixed with the food. The saliva contains an enzyme, ptyalin, 

 which is capable of transforming starch to sugar. This is not accom- 

 plished instantly, but the operation is much more rapid on cooked than 

 on raw starches. The ptyalin first splits starch into erythrodextrin and 

 maltose, one of the sugars. If time is allowed for the reaction the erythro- 

 dextrin is further acted upon, yielding maltose and another dextrin. 

 This dextrin is broken down with somewhat similar results, and the final 



143 



