CHAPTER VI 



THE CIRCULATORY SYSTEM: THE COMMON 

 CARRIER FOR THE BODY 



Although the circulatory system might logically be classed, along with 

 the nervous and endocrine systems, among the coordinating systems of 

 the body, its role as a coordinator is the result of the fact that it acts as 

 the common carrier for all of the other body parts. As a transport system 

 it is intimately involved in the functioning of all the other systems, pro- 

 viding for a rapid collection from and delivery to all the tissues of the 

 body. Its chief functions may be listed as follows: 



1. It carries digested food from the intestine (and liver) to all tissues. 



2. It carries oxygen from the lungs to the tissues and carbon dioxide 

 from the tissues to the lungs. 



3. It carries nitrogenous wastes from the tissues to the kidneys. 



4. It connects the heat-producing tissues (chiefly muscles) and the 

 heat-eliminating skin (and lungs) with the rest of the body and so 

 maintains a fairly uniform temperature throughout the body. 



5. It carries hormones (chemical messengers) from the glands where 

 they are produced to the regions of the body where they regulate 

 activity. 



6. It acts as a defense mechanism against disease-producing organisms 



by 



a. Producing antibodies. 



b. Producing white blood cells and transporting them to the invaded 

 region, where they attack and engulf certain types of disease- 

 producing organisms. 



c. Filtering out bacteria and cell debris from the blood and lymph. 



7. It protects its own system from loss of blood by forming clots in 

 cut or broken vessels. 



Essentially the circulatory system comprises a circulating fluid (the 

 blood), a muscular pump (the heart), an intricate system of pipe lines 

 (arteries, veins, and capillaries) that carry the blood from the heart to all 



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