Placentation

<p>Placentation is the formation, type and structure, or modes of arrangement of the <a href="/facts/Placenta/7XUoks1b">placenta</a>. The function of placentation is to transfer nutrients, respiratory gases, and water from maternal tissue to a growing <a href="/facts/Embryo/9QHnLVLN">embryo</a>, and in some instances to remove waste from the embryo. Placentation is best known in <a href="/facts/Viviparity/EEMn4rVx">live-bearing</a> <a href="/facts/Mammals/phSwTzBo">mammals</a> (<a href="/facts/Theria/bb9tKvHy">Theria</a>), but also occurs in some fish, reptiles, amphibians, a diversity of invertebrates, and <a href="/facts/Flowering_plant/E5eGYIvY">flowering plants</a>. In vertebrates, placentas have evolved more than 100 times independently, with the majority of these instances occurring in <a href="/facts/Squamate/sM1oc2vj">squamate</a> reptiles.
</p><p>The placenta can be defined as an organ formed by the sustained apposition or fusion of fetal membranes and parental tissue for physiological exchange. This definition is modified from the original Mossman (1937) definition, which constrained placentation in animals to only those instances where it occurred in the uterus.
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Placentation open-in-new

Placentation