Endocrine System > Mechanisms of Hormone Action

How Hormones Change Their Target Cells

Hormones are chemical messengers that invoke profound changes within target cells. How is this accomplished? There are two fundamental mechanisms by which such changes occur:

More specifically, when a receptor becomes bound to a hormone, it undergoes a conformational change which allows it to interact productively with other components of the cells, leading ultimately to an alteration in the physiologic state of the cell.

Considerable information about a how a hormone acts can be gained by knowing the type of receptor it uses. Despite the molecular diversity of hormones, all hormone receptors can be categorized into one of two types, based on their location within the cell:

Location of Receptor Classes of Hormones Principle Mechanism of Action
Cell surface receptors (plasma membrane) Proteins and peptides, catecholamines and eicosanoids Generation of second messengers which alter the activity of other molecules - usually enzymes - within the cell
Intracellular receptors (cytoplasm and/or nucleus) Steroids and thyroid hormones Alter transcriptional activity of responsive genes

Thus, if introduced to a new steroid hormone, one can quickly deduce that it has an intracellular receptor and acts upon its target cells by affecting transcription.

Additional detail on mechanism of action for these two groups of hormones and receptors are found in the next sections and in discussions about specific endocrine systems.

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