Final answer:
A hormone is a chemical messenger released by the endocrine system that travels through the bloodstream to target cells. Paracrine communication occurs between nearby cells, while autocrine communication occurs within the same cell. The endocrine and nervous systems are similar in their use of chemical signals and their role in regulating the body's physiology.
Step-by-step explanation:
A hormone is a chemical messenger released by the endocrine system that travels through the bloodstream to target cells, where it elicits a response. Paracrine communication occurs when a hormone acts on nearby cells, while autocrine communication occurs when a hormone acts on the same cell that secreted it.
The similarities between the endocrine and nervous systems include the use of chemical signals for communication and the regulation of the body's physiology. Both systems work in coordination to maintain homeostasis.