• 1 explain why the preimplantation embryo must act to preserve the function of the corpus luteum and what the mechanism is

the corpus luteum produces progesterone and it is a very important hormone required for making the uterus into a healthy place for a fetus to grow, it is also required to ensure that the next menstrual cycle (which would shed the entire uterus layer that has been built for the possibility of implantation) does not occur.

the Human chorionic gonadotropin (hCG) from implanted blastocyst (trophoblast cells) rescues the corpus luteum (the blastocyst secretes hCG) the corpus luteum then plays a crucial role of secreting progesterone until the placenta is able to do it - itself

after about 6-8weeks the corpus luteum stops producing progesterone due to diminished hCG production by the placenta, the placenta’s trophoblasts then take over the production of progesterone. when the placenta takes over progesterone production the corpus luteum diminishes

• 2 describe the events that occur between fertilisation and implantation of the blastocyst

• 3 list the tissue layers that comprise the placental membrane

comprises of three layers