938 



SPERM, OVA, AND PREGNANCY 



peripheral trophoblast (trophoblastic shell 

 and cell columns) with nourishment. 



B. ALKALINE PHOSPHATASE 



From the study of the placentas of man, 

 cats, pigs, and rodents, Wislocki and Demp- 

 sey (1945, 1946a, b) and Wislocki, Deane 

 and Dempsey (1946) concluded that a layer 

 of alkaline phosphatase intervenes between 

 the maternal and fetal placental circula- 

 tions. Wislocki and Wimsatt (1947) found 

 this to be true also in shrews, and Wimsatt 

 (1949) observed a layer located similarly 

 between the maternal and fetal circulations 

 in the placenta of the bat. In hemochorial 

 and endotheliochorial types of placentas, 

 the enzyme is usually present in the outer- 

 most layer of the trophoblast, whereas in 

 the epitheliochorial placenta of the pig it is 

 present mainly in the stroma of the mater- 

 nal placenta. Dempsey and Wislocki (1945) 

 pointed out that many substances may de- 

 pend on phosphatases for their transfer 

 across cellular boundaries, and they sug- 

 gested that a layer of different phosphatases 

 located in the placental barrier may partic- 

 ipate in the transfer of metabolites. Wim- 

 satt (1949) remarked that this view is con- 

 sonant with a variety of metabolic processes 

 which must be carried out at the placental 

 barrier and accords with the interpretation 

 of the barrier as a "selective" membrane. 

 This distribution of phosphatase in the 

 outer zone and brush border of the human 



syncytium resembles very strikingly the 

 location of the enzyme in the epithelium of 

 the small intestine and in the convoluted 

 tubules of the kidney. These three absorp- 

 tive surfaces also have well developed brush 

 borders composed of numerous microvilli. 

 Hence in the placenta, as in these latter 

 sites, alkaline phosphatase may be associ- 

 ated in the microvilli with the absorption 

 of phosphorylated compounds. Alkaline 

 phosphatase is also a component of the 

 barrier in the yolk sac placenta of rodents 

 (Hard, 1946; Wislocki, Deane and Demp- 

 sey, 1946; Padykula, 1958), although it 

 fluctuates in the vitelline epithelium at dif- 

 ferent periods of gestation. As in the human 

 syncytium, the epithelium of the visceral 

 layer of the yolk sac of rodents possesses a 

 brush border. 



In various parts of the endometrium and 

 fetal placentas of lower mammals and man, 

 Dempsey and Wislocki (1947) observed 

 differences in alkaline phosphatase reac- 

 tions following the use of a variety of sub- 

 strates. Some structures reacted with many 

 substrates whereas others reacted with only 

 one or two. It was concluded that the ob- 

 served differences could be accounted for 

 most reasonably by the assumption that the 

 tissues contain multiple enzymes of varying 

 specificity which frequently do not coincide 

 in their distribution. 



In the placentas of man, cats, rodents, 

 and shrews alkaline phosphatase increases 



Plate 15.XVII 



Lipids of the rat yolk sac 



All of the sections illustrated in Figures 15.74 to 1577 were fixed in 10 per cent buffered 

 formalin and stained with sudan black B. 



Fig. 15.74. Parietal wall and nonvillous visceral wall of the yolk sac at 13 days of gestation. 

 The parietal endoderm {p) contains minute lipid droplets and rests on an unstained 

 Reichert's membrane (r). Across the yolk sac cavity larger lipid droplets occur in the non- 

 villous visceral endoderm (v) ; however, the lipid here is less abundant than in the villous 

 portion shown in Figure 15.75. In the left border of the photograph, lipid occurs also in giant 

 cells and decidual cells of the capsularis. X 275. 



Fig. 15.75. Villous visceral splanchnopleure at 13 days of gestation. Peak storage of lipid 

 by the visceral endoderm occurs at this time (12 to 13 days). Note that the position of the 

 lipid droplets is principally infranuclear. Lipid is much less abundant in the mesenchyme and 

 mesothelium of the visceral splanchnopleure. Compare with Figures 15.76 and 15.77. Higher 

 magnification of these endodermal cells is provided in Figures 15.78 to 15.81. X 275. 



Fig. 15.76. Villous visceral splanchnopleure at 17 days of gestation. By the 17th day of 

 gestation, the villi have elongated and branched, and the lipid content of each endodermal 

 cell has decreased. The cells toward the tip of the villus tend to have more lipid than those 

 at the base. The droplets remain infranuclear. Compare with Figures 15.75 and 15.77. X 275. 



Fig. 15.77. Villous visceral splanchnopleure at 19 days of gestation. The endodermal cells 

 are quite free of lipid droplets. There is a background sudanophilia which is mostly concen- 

 trated in the mitochondria. Compare with Figures 15.75 and 15.76. X 275. 



