The elastic fiber system in the human placenta with special reference to elastic type blood vessels

Abstract

Generally, elastic fibers are part of a so-called elastic fiber system. This system includes elastin (a homogenous component), elaunin (elastin connected to microfibrils) and oxytalan fibers. Recently, we have demonstrated elastic tissue fibers as an essential component of the perivascular contractile sheath (PVCS) also in human placental stem villi. In fetal placental blood vessels, the findings about elastic tissue fibers are contradictory and no information exists about oxytalan fibers in the human placenta. Therefore, we reinvestigated the distribution of the elastic fiber system in the blood vessels of the umbilical cord, chorionic plate and stem villi. Using unfixed orcein-stained cryostal sections of term placentae, we have found a well developed elastic fiber system in fetal blood vessels. It is not possible to discriminate between arteries and veins by morphological criteria and/or the distribution of elastic fibers. After oxidation with peracetic acid additional orcein-stained fibers, were detected in Wharton's jelly and in the placental stroma. The high amount of elastic fibers throughout umbilical and placental blood vessels makes it reasonable to postulate the existence of elastic type blood vessels. Nevertheless, the great range of distribution varieties and the differing amount of elastic fibers in the blood vessels of all investigated placentae was striking. Within stem villi, there exists a longitudinal and circular vascular (inner) and a longitudinal extravascular (outer=PVCS) elastic fiber system. These two systems are ‘connected’ with the smooth muscle cells in both systems, thus forming two contractile myofibroelastic subsystems of a large overall placental myofibroelastic fiber system, in which tightly regulated cellmatrix interactions exists.