A new approach to the areolar structures in the pig placenta: histochemistry and development of mucous areolae

The pig placenta contains specific structures such as regular and irregular areolae, vesicles and cysts. On the basis of histochemical reactions it can be stated, that irregular areolae, vesicles and cysts differ from the regular areolae. Trophoblast of all the former structures and the substance filling their cavities contain glycosoaminoglycans with sulphuric acid residues (acid mucopolysaccharides). The regular areolae contain PAS-positive glycoproteins and active acid phosphatase. The acid mucopolysaccharides were also observed in the small trophoblast areas with vacuolized cells (TAVC) in the early placenta (18-20 days post coitum). The histochemical features of the investigated structures allow to observe the differentiation and development of TAVC in irregular areolar structures, vesicles and cysts in placentas from the time of implantation until the last day of gestation. Some of these structures fuse with regular areolae forming large irregular areolae described in the literature. The uterine epithelium covering all these structures forms festoon-like folds covered with the brush border. All the structures containing acid mucopolysaccharides can be termed the mucous areolae.