And that means they cannot actually pass across the plasma membrane of the target cell because the plasma membrane is made predominantly of hydrophobic tails of hydrophobic fatty acids. So that basically means peptide hormones bind on to receptor proteins found on the plasma membrane of the target cell. And once they bind, they can create some type of change. For example, they can open up a channel protein that will change an ion concentration, or they can basically use some type of secondary messenger system that uses some type of secondary messenger, such as cyclic amp, to create some form of change. Now, the second type of hormone that we're going to discuss is our steroid hormone. Now, the steroid hormone is basically synthesized from cholesterol or from some type of lipid.