Placenta Umbilical cord Placenta Maternal blood in the
Placenta & Umbilical cord
Placenta Maternal blood in the intervillous space Cross section of villus Fetal blood vessel Extra embryonic mesoderm Trophoblast
Umbilical cord Amnion Umbilical artery Wharton’s jelly Left umbilical vein
Placenta: A cross section through the placenta at five months of pregnancy shows cut sections of several chorionic villi. Each villus is covered by trophoblastic epithelium composed of outer layer of syncytiotrophoblast and inner layer of cytototrophoblast. The cells of cytotrophoblast are bigger and pale staining with slightly basophilic cytoplasm. In side the villus there is embryonic connective tissue derived from extraembryonic mesoderm and fetal blood vessels which are branches of umbilical arteries and veins. Blood vessels are lined by endothelial cells.
In between the villi is the intervillous space containing maternal blood. A section through the placenta at full term shows chorionic villi with syncytiotrophoblastic covering. Cytotrophoblast starts disappearing gradually after fifth month. Fetal capillaries in the villi also are increased in number.
Umbilical cord A transverse section through the umbilical cord at full term shows an outer covering of amnion consists of flattened cells called amniotic cells. Its interior contains a mass of mesoderm which is transformed into viscid mucoid connective tissue called Wharton’s jelly consists of fine collagen fibers and ground substance with widely spaced fibroblasts. Traversing through the Wharton’s jelly are two umbilical arteries and one (left) umbilical vein. The arteries have a thick muscular coat with folded internal elastic lamina making the lumen very narrow. Lumen of the vein is wide and often collapsed.
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