How hormones work in target tissues. Relatively small, lipid soluble. Therefore, diffuse freely into and out of cells. Full effect of hormone manifested over minutes to days. Target cells have specific receptor for hormone on cell surface.
Hormone binds to receptor and causes a second messenger to be released within the cell.
D. Examples of hormone control 1. ADH enters bloodstream. Secretion of insulin and glucagon is controlled directly by the concentration of glucose in the blood. Requires daily injections of insulin. Medulla develops from neural tissue and its secretion is controlled by sympathetic nerves.