The placenta develops during pregnancy and functions as the life support system for the foetus

• It facilitates the exchange of materials between the mother and foetus and it secretes hormones to maintain pregnancy after the corpus luteum has degenerated
  

• By completing these actions, the placenta allows the foetus to be retained in the uterus to a later stage of development than in mammals that do not develop a placenta
  

Structure of the Placenta

• The placenta is a disc-shaped structure that is composed of a combination of maternal and foetal tissues
  

• Maternal blood pools from open-ended arterioles into intervillous cavities within the placenta called lacunae
  

• Chorionic villi from the foetus extend into these pools of blood and mediate the exchange of materials between the foetus and the mother
  

• Exchanged material is transported from the villi to the foetus via an umbilical cord, which connects the foetus to the placenta
  

• Upon birth, the placenta is expelled from the uterus with the infant – it is then separated from the infant by severing the umbilical cord (the point of separation becomes the belly button)