Regardless of the size of the protein hormone, it is inevitably too big to pass through the membranes of the target tissue's cells. Instead of entering cells, the protein hormones bind to the cell membrane , using specific receptor sites. The cAMP diffuses through the cell's cytoplasm, binds with enzymes there and triggers some sort of metabolic response . The nature of the response depends on the type of cell. Steroid hormones are different chemicals.
Thier structure is based on a molecule similar to cholesterol .
Because they are small, lipid soluble molecules, steroid hormones can pass through the lipid portions of cell membranes and enter the cell's cytoplasm . The hormones bind with receptor molecules in the cytoplasm then diffuse to, and enter , the nucleus . Once in the nucleus, the hormone-receptor complex can affect gene expression on the chromosomes. An understanding of the control of body temperature is also expected, but this is not a regulatory mechanism involving hormones. The Table which follows is a summary of the important human hormones to develop familiarity, as it would be reasonable for an ewxam question to give some background on one of these hormones and expect that students could use their understanding of hormones and feedback to apply that information.