PATTERNS OF THE A-V PATHWAYS 



9' 2 9 



SUMMARY 



It is apparent, from the foregoing descriptions of 

 structural organization of microcirculatory beds and 

 regulation of the flow of blood through them, that the 

 investigations have revealed more similarities than 

 dissimilarities. Minor differences among patterns 

 seem to be associated with the structural organization 

 of the tissue in which the vessels lie, but the basic pat- 

 terns remain the same. 



Although presentation of an anatomical pattern 

 that would be "typical" for terminal vascular beds 

 would be likely to meet some resistance, it does seem 

 necessary to agree on such features as arcuate or ar- 

 cade connections, gradual divestment of spiral smooth 



muscle cells along terminal arterioles to form capil- 

 laries, absence of direct association and control of 

 capillaries through nerves, and similarity of the 

 courses taken by small arteries and small veins. Also, 

 certain functional activities which regulate blood flow 

 and blood pressure through these beds must be con- 

 sidered as universal, these being spontaneous vaso- 

 constriction and relaxation of arterioles, reversal of 

 flow paths, alternation of routes of blood flow from 

 arterial to venous vessels, and variations in the filling 

 of capillary networks depending on local conditions. 

 Future investigations may permit generalizations con- 

 cerning the angles of branching in the arterial system 

 and spontaneous vasomotion in the venous system. 



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