Post-zygotic events leading to implantation and placenta formation. After implantation of blastocyst, the finger-like projections called chorionic villi, appear on the trophoblast and is surrounded by uterine tissue and maternal blood which become interdigitated with each other to form placenta. Events leading to formation of placenta. The chorionic villi and uterine tissue, after implantation become interdigitated with each other and form placenta, a structural and functional unit between embryo and maternal body. Functions of Placenta (i) It facilitates the supply of oxygen and nutrients to the foetus and removal of C02 and excretion products. (ii) It acts as an endocrine gland and secretes hormones like hPL, hCG, oestrogen and progesterone.