CHAPTER XII 

 PHYSIOLOGY OF THE BLOOD 



We have learned that the nutritious portions of the food are, 

 after digestion, poured into the blood and circulated throughout 

 the body; also that cell action results in waste which is returned to 

 the blood. Again, that tissue changes are chemical in their nature 

 and chemical action is accompanied by heat; this is imparted to 

 the blood, which can in turn convey heat to other parts. 



Here, then, are three important functions of the blood : 



1. To convey food (including oxygen from the lungs) to the 

 tissues. 1 



2. To convey waste (including carbon dioxide) from the tissues. 



3. To equalize the body temperature. Add to these: 



4. To provide water for dissolving waste substances to be 

 removed from the body by skin, kidneys, lungs and intestine. 



5. To be a medium for transporting internal secretions (page 

 263). 



6. To furnish its own remedy for hemorrhage by bearing the 

 factors of coagulation. (See page 217.) 



(The blood is a source of water supply as well as food supply 

 for the body.) 



The special functions of the blood cells have been outlined, 

 namely: The oxygen-bearing property of red cells and the phago- 

 cytic power of the white. 



Any irritation of the tissues is promptly followed by an increase 

 in the blood and lymph supply of the part, and (if long continued) 

 crowding of cells in the capillaries. The leucocytes put forth little 

 prolongations of their substance which penetrate the vessel wall, 

 and gradually the cells themselves work their way through. This 

 causes a hardened or indurated condition which will soon disappear if 

 not excessive, but with severe irritation the process goes on to inflam- 

 mation (the cells crowding each other to death) and pus results. 



It is due to the character of the capillary walls that the blood 

 cells can migrate into the tissues (diapedesis) . In case of bacterial 



1 It must not be forgotten that oxygen plays an important part in tissue changes 

 hence the importance of the blood as an oxygen carrier. 



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