The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and lizards with varying levels of development up to mammalian levels. Note, however, that the homology of such structures in various viviparous organisms is debatable at best and, in invertebrates such as Arthropoda, is definitely analogous at best.
The word placenta comes from the Latin word for cake, from Greek plakóenta/plakoúnta, accusative of plakóeis/plakoús , "flat, slab-like", in reference to its round, flat appearance in humans. The classical plural is placentae, but the form placentas is common in modern English and probably has the wider currency at present. In pre-Roman languages of tribal cultures, the placenta is often referred to the "little mother" or "grandmother," reflective of cultural values that revered the life mystery inherent in the childbearing process which bears fruit in the form of a child.
Prototherial (egg-laying) and metatherial (marsupial) mammals produce a choriovitelline placenta that, while connected to the uterine wall, provides nutrients mainly derived from the egg sac.
The placenta functions as a fetomaternal organ with two components: the fetal placenta (Chorion frondosum), which develops from the same blastocyst that form the fetus, and the maternal placenta (Decidua basalis), which develops from the maternal uterine tissue.
No comments:
Post a Comment