It's a hormone that is composed of a peptide that has a glycogen, it has a sugar component attached to that protein. Now, this protein, this hormone is released when we have a low concentration of oxygen inside our blood. And what it does is it stimulates the red bone marrow inside our bone to basically produce and release red blood cells, also known as Erythrocytes. And that's exactly why this is known as Erythropoietin, because it produces more Erythrocytes. Now, if we have more red blood cells inside our bloodstream, that means our oxygen level inside our blood will increase. So that means urethropoietin basically increases the amount of oxygen that is found inside our blood.