Answer:
A chemical regulator secreted from an endocrine gland that travels through the bloodstream to affect target cells
Step-by-step explanation:
Hormones are the chemicals that serve as signaling molecules and regulate activities of their respective target cells. Hormones are secreted by ductless endocrine glands. Being ductless glands, they release hormones directly into the bloodstream. Therefore, hormones travel through the bloodstream to reach their target cells. Binding of receptors present on or in the target cells is followed by signal transduction and generation of a cellular response.
For example, the insulin hormone is released into the bloodstream by the pancreas. The hormone stimulates the uptake of glucose by liver and muscle cells (the target cells).