So HCG and what the human corianic gonadotropin does is it goes on to the corpus luteum found in the ovaries and it causes the corpus luteum to continue to release progesterone and estrogen because these two hormones are needed to actually maintain the thickening of that endometrium. Now eventually, when the placenta actually forms, that placenta will stop releasing human coryonic natural and it will begin to release its own estrogen and its own supply of progesterone and that will ultimately allow the maintenance of that endometrium. So these are the three hormones released by the placenta. Not only that, it actually also releases a fourth hormone at the end of the pregnancy. So towards the end of the pregnancy, the placenta also releases a hormone known as the corticotropic releasing hormone or CRH. Now, what the corticotropic releasing hormone does is it goes on to the pituitary gland found in the brain and it stimulates the pituitary gland to release a hormone known as ACTH.