And so what this hormone does is it suppresses the maternal immune system, the mother's immune system, to ensure that the immune cells do not actually attack the placenta or the growing fetus. Now, the human corianic Tropin is produced strictly and only by our placenta, by the mother's placenta. And what that means is one way we can test whether or not a woman is pregnant is by testing the blood level of this hormone found inside the woman's blood. Now, let's move on to the next type of hormone known as the human placental oxygen or HPL. Now, this is also a peptide hormone. That means it's water soluble and it bonds onto the membrane of the target cell.