CHAPTER XIV 

 SECRETION AND GLANDULAR MECHANISMS 



Correlation of Secretion, Absorption, and Excretion, and their Relation- 

 ship to Osmotic Energy. The processes of secretion, absorption, 

 and excretion are distinguished from one another only by their 

 object or physiological function, and not by anything intrinsically 

 different in their nature or in the mechanism by which these pro- 

 cesses are" carried out in the body. The purpose of secretion is to 

 prepare an active substance in solution for use in assisting a process 

 which is of service to the organism in some other part, such as a 

 digestive secretion; a secretion of a substance which has a guiding 

 influence upon chemical change in other tissues, and hence affects 

 the state of activity of those tissues as, for example, the internal 

 secretions, adrenalin, secretin, etc.; or a secretion which acts by 

 mechanical means, such as the secretion of the tears in the lachrymal 

 gland, the mucous secretions on the mucous surfaces, and the serous 

 and synovia! secretions of the serous and synovia! cavities. The 

 purpose of absorption is to take up for the service of the body 

 generally and of the absorbing cells the materials in solution which 

 have been prepared and modified by the secretions. Lastly, the 

 purpose of excretion is to remove from the body materials which 

 have passed through, or been formed in, the cycle of metabolism in 

 the body, and have become waste products for which the body has 

 no further use. In addition, the purpose of excretion is to maintain 

 in normal amount and concentration in the circulating fluid of the 

 body, the blood, those products which are of service, for in abnormal 

 concentrations these useful bodies become as injurious to the living 

 cells as effete products of metabolism, or foreign substances of 

 actively poisonous nature. 



Respiration also is essentially identical in its nature with these 

 three processes, being a combination of absorption, secretion, and 

 excretion, the only difference being that the products concerned 

 in respiration exist in the form of gases before being taken into the 

 body and after being removed from it, but in the process of respira- 

 tion itself the substances concerned oxygen and carbon dioxide 



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