yd 



CHAPTER 45 



Maternal blood flow in the uterus and placenta 1 



S. R. M. REYNOLDS Department of Anatomy, University of Illinois College of Medicine, Chicago, Illinois 



CHAPTER CONTENTS 



Comparative Anatomy of Uteri 



Angiogenesis in the Uterus 



Vascular Connections of the Uterus 



Functional Implications of Venous Drainage 



Comparative Anatomy of the Placenta 



Types of Placentas 



Placental Structure and Placental Exchange 



Vascularity and Accommodation of the Products of Conception 



Menstruation 



Hormones and the Uterine Vasculature 



Uterine Contraction and Blood Flow 



Body Posture and Uterine Contractility 



Estrogen and Uterine Blood Vessels 



Uterine Innervation 



Pregnancy and the Uterine Circulation 



among the several orders of mammals, no organ 

 in the body is more varied in form and size than the 

 uterus. One may not properly speak of "the uterus" 

 as an organ in which identical physiological activities 

 take place in the fulfillment of the purpose for which 

 a uterus exists. True, the uterus permits implantation 

 of fertilized blastocysts, accommodates the products 

 of conception for a normal span of development, and 

 then delivers to the outside world an organism or 

 organisms that can survive. Specialized adaptations 

 exist among mammals in the form and function of 

 the various uterine and placental types. Such varia- 

 tions in uterine and placental structures, coupled 

 with specialized variations in cyclic activity, serve to 

 render them quite different from one another while 

 achieving a common goal, namely, the production 

 of living offspring. 



As a student of physiology, man tends to be an- 



1 Prepared and typed under USPHS Grant RG 4728. 



thropocentric; he employs many kinds of animals 

 exhibiting many types of mechanisms but, while ex- 

 amining comparative basic processes, he hopes to 

 understand himself. It is necessary, therefore, that 

 insofar as present knowledge permits, the several 

 types of form and function be considered. 



COMPARATIVE ANATOMY OF UTERI 



It is axiomatic in developmental biology that 

 ontogeny repeats phylogeny. This is to say, as one 

 passes from species A to species Z there are grades of 

 morphological complexity that can be seen. Similarly, 

 in the development of species Z, all or most of the 

 essential elements of species A, B, C, D, . . . Z are 

 observable in transition from a simple type to a 

 complex type of structure. Although this is an over- 

 simplification of the situation, it is generally true and 

 it is as easily demonstrable for the uterus as with any 

 organ in the body [Reynolds (198)]. 



Like so many viscera of the body, the uterus may be 

 characterized as starting as paired symmetrical tubes, 

 part of the mullerian duct system. In monotremes 

 (e.g., Echidnae), marsupials (e.g., Marsupialae), and 

 some rodents (e.g., Leporidae) at least, two uteri 

 remain separate throughout life, arising cephalad at 

 the caudal end of the fallopian tube and terminating 

 caudally with independent cervical openings in the 

 vagina. In other species, the caudal ends of the ducts 

 fuse mesially to form a single cervical opening in the 

 vagina. Examples of this are seen in certain rodents 

 (e.g., Mus rattus and norvegicus), carnivores (e.g., 

 Canis), ungulates (e.g., Ovis, Bovis, and Equidae) 

 and many others. Continuing the extent of mesial 

 fusion to the ultimate degree, the primates normally 

 have a single uterus, which receives two fallopian 



1585 



