Foetal Placenta

 Foetal Placenta

        The inner surface of the plate is lined by the intervillous space and is covered with trophoblast. The trophoblast is supported by layer of connective tissues which includes blood vessels radiating from the umbilical cord. It forms the umbilical (allantoic) system and distributes through the chorionic plate to the villi. The developing amnion, at the end of second month, comes in contact with the connective tissue of the chorion at every point and thus amnion gets attached to the foetal membrane of the placenta and is retained throughout the pregnancy. 

        The chorionic villi the second part of foetal tissues is of great importance as it is responsible for exchanges of all kinds taking place between mother and embryo. Initial villi are compact, short and brush-like tufts. They arise from common or main stems which develop from the chorionic membrane. The ends of all branches are called anchoring villi as they are attached and mixed with the eroded surface of decidua basalis. Branching becomes extensive in the second month forming many side branches and many free villi. During later stages, the branching is so rich that it appears like a tree with prominent trunk and main branches. Sometimes many terminal branches first fuse with the decidua basalis and then turn back into the intervillous space in a J shaped structures.

        In structures, each part of villous tree is composed of a central connective tissue core that contains vascular supply. The vascular supply includes arterioles and veinules which run as capillaries into the villous tips and fuse with each other forming a closed system. The connective tissue core is made up of two layers of trophoblast. The inner layer which lines the connective tissue, made up of a single layer of cuboidal cells, is called cytotrophoblast. This layer is also named as layer of Langhams. The outer layer which bounds the villi is known as the syntrophoblast. The rapidly expanding villous tree is in due time separated by partitions called the placental septa forming distinctive lobule known as cotyledons. The septum is a partition formed from the tissue of placenta and projects far toward the chorionic plate. It originally consists of a plate of decidual tissue but later on replaced by trophoblast. The so-called cotyledons are naturally vascular units with a net work of blood vessels. Such cotyledons number from 14 to 30 and are incompletely separated from each other by thin placental septa.