FORMATION AND ROLE OF THE PLACENTA
1.  Preparation of the uterus
  Window of receptivity

2.  Implantation (nidation)
Apposition, Adhesion
Penetration of endometrial epithelium
Invasion of decidua

3.Establishment of a hemochorial placenta
     Lacunar
Development of chorionic villi
           Intervillous
         Maternal plasma only
         Whole blood