How Do Hormones Work

Hormones act as chemical messengers in the body and are secreted into the bloodstream (1) by the endocrine glands for distribution around the body.

Each hormone acts only on a specific type of cell, that is the cell bearing the correct membrane receptor site. These are called "target cells" for the hormones. For example, the diagram above shows that a square object will not fit a round receptor (2). The diagram also shows that within the bloodstream (1) there are many different types of hormones. When a specific receptor site is not filled, that cell remains "turned off" (2). A correct hormone will eventually attach itself to a correct receptor site (3).

As a hormone attaches itself to a receptor site (4), it will initiate a "switch on" reaction within the cell cytoplasm. This results in a cascade of biochemical and molecular events (5) resulting in the final physiological effect of the hormone (6).

Some hormones last for only a few minutes, others, have a longer life. Hormones may be inactivated by the target cell itself or by the liver, and the break-down products, are either excreted or recycled and used in the further manufacture of hormones.