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HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



fig. 9. Circumferential arteries of nonpreg- 

 nant rabbit uterus. These anastomose with 

 each other laterally and supply the uterine 

 wall. [From Reynolds (199).] 



tells what the circulatory load of the gravid uterus 

 is on the maternal cardiovascular system but it fails 

 to tell how this is related to supplying fetal needs, 

 on one hand, and uterine tissue needs, on the other. 



among many types of placentas. In this way, it 

 becomes possible to account for the occurrence of 

 fetal erythrocytes in the maternal blood and vice 

 versa (see below). 



PLACENTAL STRUCTURE AND PLACENTAL EXCHANGE 



Flexner and associates [Flexner & Gellhorn (81), 

 see Reynolds (198)] have found wide differences in 

 the rates of transfer of given electrolytes across various 

 types of placentas. Thus, in the ninth decile of gesta- 

 tion the transfer of Xa is 0.026 mg per hour per gram 

 of placenta in the so-called epitheliochorial placenta 

 and 6 to 8 mg per hour per gram of placenta in the 

 hemochorial placenta. Intermediate rates of transfer 

 are found in the syndesmochorial and endothelio- 

 chorial placentas. Although it is believed by some 

 that Grosser's classification of placental types has 

 outlived its usefulness [cf Amoroso (6)], it is possible 

 that the classification expresses a general tendency 

 toward morphological organization and functional 

 capability that is not entirely negated by dwelling on 

 details of isolated microscopic fields either in the 

 several types of placentas or in any one placenta. One 

 may accept the fact that diere are differences in 

 morphology, but these are not sharply defined either 

 within one placenta at various stages of pregnancy or 



VASCULARITY AND ACCOMMODATION OF THE 

 PRODUCTS OF CONCEPTION 



The adaptation of the vasculature of the nonpreg- 

 nant uterus to the changes of gravidity is met in 

 various ways in the several types of uteri: through 

 growth and enlargement of the blood vessels [Orsini 

 (164), Wermbter (241), Schwarz & Hawker (218)] 

 and by physical rearrangement of blood vessels as 

 the uterus enlarges and changes the spatial orienta- 

 tion of the uterine blood vessels, especially as the 

 uterus is finally stretched in the latter part of preg- 

 nancy. In all nonpregnant uteri numerous arteries 

 are tortuous, coiled, or undulating [Ramsey (180)]. 

 These tortuosities in the blood vessels permit their 

 extension to accommodate in part the increase in 

 size of the uterus. In sheep, one or two of the uterine 

 arteries approach each cotyledon. The vessels divide 

 into five or six trunks and pursue a tortuous course 

 in the submucosa before dividing again and entering 

 the cotyledon [Barcroft & Barron (19)]. The early 

 pattern of these structures seems not to change during 



fig. 10 (facing page). Distribution of fetal arteries and veins to cotyledons of placenta of Pere 

 David's deer. Note that arteries and veins are of about equal size and number, indicating about 

 equally rapid flows of blood in them. 1. Three injected cotyledons. Nearly natural size. 2. Section 

 through middle of placentome. Masson stain. Natural size. 3. Drawing of three injected villi, re- 

 moved from placentome. Central vessels of the villus and the intraepithelial capillary network are 

 shown. 4. Section through fetal zone of placentome showing stem villus and to vessels. X50. Left 

 and right, thin strands of maternal connective tissue from which epithelium is removed. [From Harri- 

 son & Hamilton (95). Courtesy Cambridge University Press.] 



