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. Now, this is produced by the placenta and it plays two very important functions. Firstly, it basically controls and regulates the concentration, the level of glucose, fatty acids and amino acids in the blood plasma of the mother. And this is done to basically ensure that the fetus has a constant supply of energy that it basically needs to grow and develop.