894 



SPERM, OVA, AND PREGNANCY 



itself in the puerperium from the basal zone 

 and the deep residual portion of the stratum 

 spongiosum. 



The trophoblast forms the parenchyma of 

 the placenta and the major element of the 

 placental barrier. It mediates the metabolic 

 exchange between mother and fetus. It pro- 

 vides for the nutrition of the embryo, at 

 first, by the local destruction and absorp- 

 tion of the uterine decidua, and later, by 

 transmission of metabolites through the 

 syncytial trophoblast from the maternal to 

 the fetal blood streams. It serves also as 

 an avenue for the excretion of various fetal 

 waste products. The human trophoblast is 

 also an important endocrine organ which 

 produces steroid hormones, chorionic gon- 

 adotrophin and other hormones. 



B. CHORIONIC VILLI 



1. Trophoblasts: the Langhans Cells 



These conspicuous cells which possess 

 large nuclei constitute a germinal bed in 

 which mitoses are frequently seen and from 

 which in the early part of gestation the syn- 

 cytium is evidently derived. The Langhans 

 cells gradually diminish in number, but 

 some of them survive until the end of ges- 

 tation (Wislocki and Bennett, 1943; Wis- 

 locki and Dempsey, 19551. Electron micro- 

 graphs show that the Langhans cells are 

 closely apposed on their outer surfaces to 

 the syncytium and on their basal surfaces to 

 the basement membrane of the stroma of 

 the chorionic villi. 



The cytoplasm of the Langhans cells is 

 characteristically chromophobic (Wislocki, 

 Dempsey and Fawcett, 1948 j, exhibiting 

 only faint cytoplasmic basophilia (Fig. 

 15.10), little affinity for acid dyes (Fig. 

 15.9), and no metachromasia. This lack of 

 basophilia correlates with their meager en- 

 doplasmic reticulum, i.e., ergastoplasm 

 (Wislocki and Dempsey, 1955) . In the first 

 4 to 6 weeks of gestation their cytoplasm 

 contains a considerable amount of glycogen, 

 stainable by the PAS method. This glycogen 

 subsequently disappears. Except for slight 

 staining adjacent to the nuclear membrane 

 (Fig. 15.54) , the cytoplasm is negative with 

 the PAS reagents following the removal of 

 glycogen. There are no lipid droplets. 



There is a moderate number of rod- 



shaped and granular mitochondria (Wis- 

 locki and Bennett, 1943) . In electron micro- 

 graphs, the mitochondria of the Langhans 

 cells are relatively few in number but larger 

 than those in the syncytium. A moderate 

 degree of succinic dehydrogenase activity 

 is demonstrable in these cells (Figs. 15.37 

 and 15.38). The Golgi apparatus is situated 

 on the side of the nucleus toward the syn- 

 cytium (Baker, Hook and Severinghaus, 

 1944). 



The cytoplasm is faintly stained in the 

 reaction for protein-linked sulfhydryl 

 groups (Figs. 15.33 and 15.34). The acid 

 and alkaline phosphatase activities are of 

 a low order. 



2. Trophoblastic Syncytium in the First and 

 Second Trimesters of Pregnancy 



Free surface. The syncytium constitutes 

 a broad layer of cytoplasm without cell 

 boundaries and possesses small, irregularly 

 shaped, darkly staining nuclei which are 

 rather uniformly dispersed in its inner zone 

 (Fig. 15.9). It possesses an outer surface, 

 facing the intervillous space, which is ex- 

 tremely variable in structure, ranging from 

 a foamy, vacuolated border possessing deli- 

 cate streamers and fronds, through various 

 intermediate appearances, to regions where 

 it bears a well defined brush border (Wis- 

 locki and Bennett, 1943). In the earliest 

 stages the former appearances predominate, 

 but as gestation advances, the brush border 

 increases in amount. It was suggested by 

 Wislocki and Bennett that these variable 

 surface appearances in fixed material indi- 

 cate that the living syncytial cytoplasm 

 is pleomorphic and plastic. The parts that 

 are foamy and vacuolated and possess 

 streamers are probably constantly moving 

 and flowing, a physiologic activity that 

 would promote the alisorption of fluid and 

 metabolites from the intervillous space by 

 the process of pinocytosis (Wislocki and 

 Bennett, 1943). In confirmation of this, 

 observations of explanted bits of placenta 

 growing in tissue cultures show that the cy- 

 toplasm of both the syncytial and cellular 

 trophoblast moves quite actively, giving 

 rise to a variety of streamers and thread- 

 like processes (Friedheim, 1929; Jones, Gey 

 and Gey, 1943) . 



The ultrastructure of the free surface of 



