Meaning of "placenta" in the English dictionary

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, fights against internal infection and produces hormones to support pregnancy. Placentas are a defining characteristic of placental mammals, but are also found in some non-mammals with varying levels of development. Note, however, that the homology of such structures in various viviparous organisms is debatable and, in invertebrates such as Arthropoda, is analogous at best. The word placenta comes from the Latin word for cake, from Greek plakóenta/plakoúnta, accusative of plakóeis/plakoús – πλακόεις, πλακούς, "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. Prototherial and metatherial mammals produce a choriovitelline placenta that, while connected to the uterine wall, provides nutrients mainly derived from the egg sac.