What is the primary function of hormones in the body?

Hormones are biochemical substances that are secreted directly into the bloodstream by glands in the endocrine system. Their primary function is to influence growth, metabolism, and the regulation of various body processes, such as mood, immune function, and reproductive functions. Hormones act as messengers, communicating information from one part of the body to another, which helps maintain homeostasis and ensure that physiological processes occur in a coordinated manner.

For instance, growth hormones help regulate growth and development, while insulin plays a critical role in controlling blood sugar levels. By balancing various functions, hormones are essential for maintaining the body's internal environment and responding to external changes.

The other options address functions that are not primarily hormonal. Digesting food in the stomach is primarily the role of enzymes and acids, energy for physical activity typically comes from carbohydrates and fats, and while hormones can have roles in cell signaling, they are not structural components of cells. Each of these functions is critical, but they fall outside the direct scope of hormonal activity.