The placenta functions as all of the following, except 

The placenta does not function as digestive gland.

The placenta acts as lung as it facilitates the supply of oxygen and also removal of carbon dioxide.

It functions as kidney as  it helps in removal of excretory/waste materials produced by the embryo.

Placenta also acts as an endocrine tissue and produces several hormones like human chorionic gonadotropin (hCG), human placental lactogen (hPL), estrogens, progestogens, etc.