HOW STEROID HORMONES BIND TO CELLS
Hormones are chemical messengers, secreted by endocrine glands, which alter the activity of other cells in the body. Hormones can be either proteins or peptides, fatty acid derivatives, steroid derivatives, or modified amino acids. Some hormones are referred to as tropic hormones because they are able to stimulate the production of other hormones.

The mechanism that controls hormone secretion is negative feedback. In a negative feedback system, some change in a steady state releases a hormone and triggers a response that balances out the initial change, returning the system to homeostasis.

Hormones act only on cells that are able to bind to the hormone, based on the presence or absence of receptors for the hormone on the cell membrane. Steroid hormones and thyroid hormones, because of their lipid solubility, bind directly to their receptors in the cytoplasm of target cells. Once bound to its receptor, the steroid hormone-receptor complex travels to the nucleus, where the steroid hormone-receptor binds to promoters of genes, either stimulating or repressing transcription.