Chorion (gr. chorion), hairy sheath, the second shell of the fruit, which, unlike the decidual, exclusively fetal origin. The chorion is vital makeshift the body of the embryo that develops earlier than the rest of the bodies, and begins to function in the early stages of embryogenesis, through trophic, respiratory, excretory and protective functions.
After the implantation of the egg submerged part of the trophoblast already in 7-th day of embryo development (see) gives away from its outer surface of the primary NAP, which is the protrusion simpleslideshow trophoblast layer. By the 12th day of embryogenesis in trophoblast there are items of mesenchyme (see): from this moment begins to develop the chorion. By the end of the 2nd week of pregnancy processes of the mesenchyme grow into trophoblast and covered his appendages. Occur secondary NAP, which are immersed in majorsince space. Epithelial cover secondary CVS formed by trophoblasts consisting of two layers: the inner called layer Langhans, or cytotrophoblasts, and outdoor syncytial (plasmodiophorales, or resorption syncytium). Layer Langhans formed cubic cells; in syncytial layer has vacuoles, mitochondria and large emofilia grain. The enzymatic activity of the chorion is associated with syncytial layer. Since the end of the 2nd month of pregnancy cells Langhans gradually disappear, and by the end of the 4th month of epithelial cover CVS consists only of syncytium; according to other data, the cells Langhans saved up to 7-8-th month of pregnancy.
In the area well vascularizing decidua basalis (see Decidual shell) the chorionic villi are in the best conditions of nutrition and grow more pompous, forming branching chorion (chorion frondosum). Branchy Rorion and spliced with him decidua basalis form the placenta (see). NAP branched chorion anastomose with each other lateral branches, intertwined in General a complex system.
In the chorion are alkaline and acid phosphatase (in the cytoplasm and nuclei of both layers trophoblast and stroma CVS), glycogen, neutral and acid mucopolysaccharides (cytotrophoblast and connective tissue CVS), lipids (mainly in syncytial layer and stroma cells CVS), iron salts - as associated and not associated with organic substances. Localization of organic compounds of iron in the cytoplasm and nuclei syncytial trophoblast layer proves that of all the sites Vorsin the highest consumption of oxygen occurs in syncytia. These histochemical data to account for most of the enzymatic activity of the trophoblast, its ability to destroy maternal blood vessels and to penetrate the thick falling shell.