Hormones are small molecules that travel throughout the body and act as chemical messengers. They are responsible for regulating body activities like growth, sexual functions, and digestion. Hormones can vary widely in their chemical structures. Water soluble hormones are generally amino acid and peptide based in structure and are relatively soluble in water. They travel freely in the bloodstream but cannot pass through nonpolar cellular membranes. As a result, they tend to bind to receptors on the surface of the membrane which then sends a chemical signal into the cell to elicit a response.