UTERINE BLOOD FLOW 



'597 



pregnancy except that the uterus is distended as 

 pregnancy advances and increases steadily. 



Harrison & Hamilton (95) have demonstrated 

 especially well the relation of maternal and fetal 

 blood vessels to each other in a deer. (See below for 

 discussion of the fetal blood vessels in the hemochorial 

 placenta.) 



In the monkey, as the endometrium becomes 

 thinner because the uterus is distended by the con- 

 ceptus, the arteries become extended and the number 

 of arterial connections with the intervillous spaces 

 increases by development of smaller branches. Sub- 

 sequently, the ends of adjacent vessels coalesce to 

 form terminal dilations from which a single opening 

 with a large accumulation of lining cells passes 

 through the basal decidual plate into the maternal 

 lake of blood [Ramsey (183)]. In the human, similar 

 arrangements exist [Lundgren (137)]. Arterio-arterial 

 shunts in the uterus exist among these vessels [Heckel 

 & Tobin (100), Reynolds (199)]. As pregnancy 

 advances, the number of arterial openings into the 

 villous lake decreases substantially. Uterine blood 

 vessels, along with all other tissues of the uterus, grow 

 by hypertrophy and hyperplasia of their component 

 parts during pregnancy [Reynolds (198)]. The cause 

 of this is partly hormonal, partly the result of disten- 

 tion of the tissues. Hormones and distention interact 

 to effect the growth response of the uterus during 

 pregnancy (198). 



For many reasons, therefore, the physiologist who 

 would study blood flow would be well advised to 

 appreciate the complexity of structural and functional 

 factors involved in the uterus in different functional 

 states. 



The adaptation of the uterine vasculature to the 

 uterus during pregnancy has been especially well 

 studied in the rabbit [Reynolds (199)], which is 

 typical of the uterus duplex and, with some modifi- 

 cations, to the uterus bicornis. A certain parallel 

 exists also with changes that occur in pregnancy in the 

 uterus simplex [Ramsey (187)]. 



In the rabbit, the vascular system of the uterus 

 consists of large vascular channels which intercom- 

 municate freely, both longitudinally along the meso- 

 metrial border of the uterus and circularly along the 

 length of the uterus. This is well shown by Orsini 

 (164) in the hamster. Of these large channels, the 

 mesometrial arcuate vein is concerned primarily with 

 draining the region of the uterus to which placental 

 sites are attached. The lateral arcuate veins on each 

 side of the uterus drain the larger part of the uterine 

 wall. Each of these vascular beds is supported by the 

 same incoming arteries and drained by the veins of 

 the broad ligament. The implication of such an ar- 

 rangement is clear. If, due to distention, the blood 

 flow is reduced in one area (i.e., the peripheral vas- 

 cular resistance increases), the flow of blood to the 



ARTERIES 



MARGIN OF INTERVILLOUS SPACE 



TERMINAL SAC 



ARCUATE ARTERY 



PERITONEAL SURFACE 



[B] 6th WEEK 



a 



3-d WEEK 



MARGIN OF INTERVILLOUS SPACE 



BASE OF ENOOMETRIU 



PERITONEAL SURFACE 



5^ 



A 



MARGIN QF INTERVILLOUS SPACE , 



SPIRAL ARTERY 



(PARTIALLY 



UNCOILED) 



[D]l5'h WEEK 



SP pa l ajjter. [uncoiled; 



MARGIN OF INTERVILLOUS SPACE 



6th WEEK 



ARCUATE ARTERY 



ff]l9"> WEEK 



fig. 1 1 . Pattern of arterial supply to basal plate of the monkey placenta at different stages of 

 pregnancy. [Permission of Ramsey (181).] 



