Placenta

PLACENTA

  • Placenta is the intimate apposition or fusion of extra embryonic membranes to the maternal tissue for the physiological processes of respiration, nutrition and excretion. In addition placenta protects the embryo.

Foetal membranes (or) Extra Embryonic membranes

  • Yolk Sac: The endoderm lines the inner border of the blastocyst, converting the blastocoele into the yolk sac cavity.
  • Amnion and Chorion: The newly formed chorionic sac in the early stages encloses a large cavity – the extra embryonic coelom (exocelom) that lies between chorion and amnion. In later stages the amniotic membrane fuses with chorion in the cow, ewe and sow to form an amniochorionic membrane.
  • Allantois: The allantois grows into the exocoelom and surrounds the amnion. During this period the yolk sac regresses. The allantois which is highly vascularised by foetal vessels, fuses with the chorion bringing foetal vessels to the periphery of chorionic sac and thus into closer apposition with the maternal tissue. This is the formation of the chorioallantoic membrane.
  • The compound allantochorionic membrane together with the uterine tissue is designated as chorioallantoic placenta and is classified on the basis of its form and also the number of layers of tissue separating foetal and maternal vascular system viz., degree of placental union.
  • The chorion which is beset with vascular villi that are in intimate association with the endometrium, constitutes the placenta which sub serves the functions of nutrition, respiration; excretion – and protection of the embryo.

Last modified: Tuesday, 8 May 2012, 6:57 AM