THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

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The wall of the chorionic sac becomes sticky about the lTth day
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and adheres to the convex outer surface of the materna'r caruncres,which have
circular elevations on the endonetrium, often pigmented . ..
Modification of the cytorogica] character of the naternar
caruncular epÌtheìium is fjrst apparent on the l6th day of pregnancy.
A reduction in the number of epitheliaì cells is usualìy associated
with nuciear vacuora*on, sweiling and dislntegration. The subepithe.riaì
stroma becomes oedematous and contains increased number of eosinophiìs.
The structural appearance of the chorionic sac at day
17 to 22 is a simple or pseudos trat i fi ed cuboidaì ep.ithelium. pleomor_
phism of the epithellum .ls apparent and ls probabìy related to the
differentíation of the epithelium ínto two cet types: the uninucreate
cuboidal trophoblast, and the rounded binucleate giant ceìls.
The cuboidal epithe'l iar ce'ils constitute about four-fifths
of the trophobìast cell population and possess a large irregular.ly_
shaped nucleus with a single rarge nucreolus and flneìy dispersed chromatin.
Their cytopìasm is moderatery dense and contains, predominantly in the
apical part of the ceìr, ovoid to elongated mitochondriar profì.res with
a dense matrïx and moderate numbers of rameüar cristae. The Gorgi bodìes
are sma'll and are located ìateralìy in the cytoplasm of the cell. Adjacent
lateral plasma membranes interu,eave in a comprex manner .in some areas
and exhibit infrequent desmosomes and varying degrees of separati on. Cì ose
to the maternar tissue these membranes posses nurnerous m.rcrovlUl lnter-
digitating with corresponding naternar microvlili. The cuboida.r ceils can
further divide into two types. At one extreme are the rnajorrty of the cerìs,