Which statement best describes a hormone in the provided material?

**Hormones** are chemical messengers secreted by specialized cells. The material identifies endocrine cells, neurons, and immune-system cells as possible sources. They are not defined as nutrients or membrane structures, and their signaling is not limited to communication between neurons.\n\n**Key takeaway:** A hormone is a chemical messenger whose source and route can vary.\n\n**Glossary:** **Endocrine cell**: A cell that releases chemical messengers; **chemical messenger**: A molecule that conveys information between cells or organisms.