6 shows the typical organization of a terminal villus, whereas Figs. 7 and 8 show the ultrastructural appearance of the syncytial trophoblast. Human term placenta . In some areas the syncytium is extremely attenuated, and often a fetal capillary is associated with these areas. The fetal capillaries are sinusoidal , i.e., they are irregular and have a large diameter.
Cytotrophoblast cells are present, but difficult to detect.
Placental macrophages are still present, but are not vacuolated as in early placentas. The umbilical cord is covered by a single layer of epithelium from the amnion and contains a mucous connective tissue core. Each of the two umbilical arteries has a muscular tunica media but an indistinct elastic membrane. The umbilical vein appears less constricted than the umbilical arteries. Slide b-44 is a plastic section of placental villi in situ at term, with much of the maternal blood remaining.