BLOOD: SOME FUNCTIONAL CONSmERATIONS 



DOUGLAS M. SURGENOR, Department of Biological Chemistry, Harvard 

 Medical School, Boston, Massachusetts 



The functions of blood reflect its unique physical and 

 chemical relation to the tissues of the body. In biochemical 

 terms it can be regarded as a continuously circulating tissue 

 phase which is in dynamic equilibrium with the tissues it bathes. 

 It supplies the tissues with the sustenance they require for the 

 performance of their physiological functions; it provides the 

 means whereby important intermediates and specific tissue 

 products such as the hormones are transported to other parts of 

 the organism; and it removes the waste products of metabolism. 

 A striking feature of this transport facility is the efficiency with 

 which the transported substances are delivered to specific 

 destinations throughout the body. The blood in turn depends 

 upon the tissues for a continuous supply of new cells and proteins 

 and for the removal and breakdown of old, since it does not 

 possess regenerative facilities of its own. This dependency is 

 often so direct that the composition of the blood reflects the state 

 of activity of the hematopoietic tissues. 



A second major role of blood is the defense of the organism 

 against invading bacteria, viruses, and other foreign substances. 

 Here again distinct and highly specialized systems exist, based on 



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