True or False: An endocrine hormone is released into circulation to act on a target organ.

The statement is true because endocrine hormones are specifically designed to be released into the bloodstream, where they can travel to distant target organs and tissues to exert their effects. This mode of hormone action is central to the endocrine system, which uses hormones to regulate a wide range of physiological processes, including metabolism, growth, and mood.

For instance, when a hormone like insulin is secreted by the pancreas, it enters the bloodstream and travels to various tissues, primarily the liver, muscle, and fat cells, where it promotes the uptake of glucose. This illustrates how the endocrine system uses the circulatory system as a means to deliver its regulatory signals across the body.

In contrast, hormones released by other systems, such as the nervous system, may act locally and much more quickly than endocrine hormones. This distinction highlights the unique role of endocrine hormones in maintaining long-term regulatory processes within the body.