CHAPTER 27 



Patterns of the arteriovenous pathways 



MARY P. WIEDEMAN 



Department of Physiology, Temple University 

 School of Medicine, Philadelphia, Pennsylvania 



CHAPTER CONTENTS 



Definitions 



Techniques for Microscopic Observation of Small Blood Vessels 



Hamster Cheek Pouch 



Transparent Chamber 



Fused Quartz Rod 



Bulbar Conjunctiva 



Rat Mesoappendix 



Bat Wing 

 Structure of Terminal Vascular Beds 



Microcirculation in the Bat Wing 



Microcirculation in the Rabbit Ear 



Microcirculation in the Mesentery 



Microcirculation in the Hamster Cheek Pouch 



Microcirculation in Skeletal Muscle 



Microcirculation in Myocardium 



Microcirculation in Skin 



Microcirculation in Stomach and Intestine 



Microcirculation in the Bulbar Conjunctiva 



Microcirculation in the Spleen 



Microcirculation in the Lung 



Microcirculation in the Cochlea 



Preferential or Thoroughfare Channel 



Arteriovenous Anastomoses 

 Blood Flow Through Terminal Vascular Beds 



Capillary Contractility 



Vasomotion 

 Summary 



although capillary vessels in living animals have 

 been observed microscopically for three hundred 

 years, there is a great diversity of opinion regarding 

 the structure and function of minute vessels in terminal 

 vascular beds. Actually, a survey of the descriptions 

 of patterns formed by capillary networks and the 

 flow of blood through them in a wide variety of tissues 

 and organs reveals great similarity in vascular 

 patterns and also in the manner in which blood flows 



from arterioles through capillary nets on to collecting 

 venules. This similarity of structure and function 

 leaves the impression that acceptable generalizations, 

 applicable to these terminal beds, must be developed 

 in order that future studies may prove profitable. 



It is well known that unnecessary disagreement 

 arises from lack of uniformity in terminology. It is 

 equally obvious that unnecessary confusion arises 

 from assigning complex functions to isolated com- 

 ponents of a specific vascular bed when, in truth, 

 both the activity and the structure are common 

 features of small blood vessels anywhere. 



DEFINITIONS 



Any attempt to supply a list of universally accept- 

 able definitions of vascular structures would be 

 useless, and yet it is necessary to present some general- 

 izations regarding current usage of terms before 

 describing the types and variations of structural 

 patterns that connect distributing arteries and col- 

 lecting veins. 



The term "microcirculation" is used to designate 

 blood flow through small vessels at the capillary level 

 (48). The microcirculatory bed is the ultimate portion 

 of the cardiovascular system which is generally 

 accepted as being concerned with the transfer of 

 gases and nutrients and the removal of metabolic 

 waste products. Minute precapillary arterioles and 

 postcapillary venules are included with the capillaries 

 as major components of the microcirculation (53). 



Terminal arterioles are the final arterial ramifica- 

 tions, the branchings of which continue as non- 

 muscular capillary vessels (88). They are further 



891 



