Figure 11.
Umbilical cord contains the umbilical vessels (two arteries and vein) surrounded by the jelly of Wharton and connected embryo to the placenta. The umbilical arteries carry poorly oxygenated blood from embryo to the placenta. The umbilical vein carries well-oxygenated blood from placenta to the embryo. The connective tissue of the umbilical cord is rich in mucopolysaccharides and functions as a protective layer for the blood vessels.
The walls of the arteries are muscular and contain many elastic fibers, which contribute to a rapid constriction and contraction of the umbilical vessels after the cord is tied off.
AMNION
Figure12. Amnion on the fetal side of placenta (the amniotic epithelium in this location is simple columnar)
The epithelium of an amnion at early stages is simple squamous. On 3-rd month of an embryogenesis the epithelium is transformed in simple columnar epithelium. The epithelium of an amnion in a region of a placental disk has secretor function. The basic function of epithelium of an extraplacental amnion is resorption of amniotic fluid.
In a stroma of amniotic membrane distinguish a basal membrane, a layer of the denseconnective tissue and a spongy layer of loose fibrillar connective tissue linking amnion with a chorion. In a layer of the dense connective tissue it is possible to discharge an ancellular part laying under a basal membrane and a cellular part. Cellular part consists of several layers of fibroblasts between which is embedded some collagen and reticular fibers. The spongy layer is formed by a mucous connective tissue.
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