Submitted to: Encyclopedia of Animal Science
Publication Type: Book / Chapter
Publication Acceptance Date: 11/10/2003
Publication Date: 11/1/2004
Citation: Ferrell, C.L. 2005. Placenta: Types. In: Pond, W.G., Bell, A.W., editors. Encyclopedia of Animal Science. Marcel Dekker,Inc., New York, NY. p. 716-718.
Technical Abstract: The placenta is unique among mammalian organs for a number of reasons. Placentas of different species exhibit a broad diversity of structure that includes differences in cellular organization, shape, and pattern of distribution over the uterine endometrium. Placentas have been classified into three main types based on the number of layers separating maternal and fetal blood. Alternatively, placentas have been classified into four main types that relate to the degree to which the placenta is localized into a single discrete organ. Placentas differ greatly among species, yet all have the same task in maintaining and supporting embryonic and fetal growth, and appear to be equally successful in doing so.