Changes

==Introduction==

==Introduction==

The formation of the placenta is referred to as the "second" or "embryonic" period of pregnancy and describes the establishment of a fully functional placenta. The placenta is an apposition of foetal and parental tissue for the purposes of physiological exchange.  There is little mixing of maternal and foetal blood, and for most purposes the two can be considered as separate.

The formation of the placenta is referred to as the "second" or "embryonic" period of pregnancy (after the implantation period) and describes the establishment of a fully functional placenta. The placenta is an apposition of foetal and parental tissue for the purposes of physiological exchange.  There is little mixing of maternal and foetal blood, and for most purposes the two can be considered as separate.

==Formation==

==Formation==