What is a hormone?

A hormone is defined as a chemical that regulates bodily functions. Hormones are produced by glands in the endocrine system and are released into the bloodstream, allowing them to travel to various organs and tissues to influence functions such as growth, metabolism, reproduction, and mood. For example, insulin is a hormone that helps regulate glucose levels in the blood, demonstrating how hormones play a vital role in maintaining the body's homeostasis.

The other options refer to different concepts: a muscle type pertains to the classification of muscle tissue (such as skeletal, cardiac, or smooth), a type of food refers to substances consumed for nourishment, and a structural component of cells generally relates to molecules like proteins or lipids that make up cell membranes or structures, rather than regulatory substances like hormones. Understanding what hormones are and their significance in the body is crucial for grasping concepts related to biology and human physiology.