Now, an actual hormone that is released by the cells in the kidney is Erythropoietin, as well as calcitriol. Now, Erythropoietin is released by special type of cell inside the kidney known as the extra Grammylarl Messangel cells. Now, these cells release our Erythropoietin, which is basically a glycoprotein hormone. 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.