Which body system regulates metabolism, growth, and development?

The endocrine system is responsible for regulating metabolism, growth, and development through the secretion of hormones. Hormones are chemical messengers that travel through the bloodstream to various organs and tissues, influencing a wide range of physiological processes. For example, hormones such as thyroid hormones play a crucial role in metabolism by controlling how the body uses energy, while growth hormones are important for growth and development during childhood and adolescence.

In contrast, the respiratory system is primarily involved in gas exchange, allowing oxygen to enter the body and carbon dioxide to be expelled. The digestive system focuses on the breakdown of food to provide nutrients for energy, growth, and cellular repair, but it does not directly regulate metabolism or hormone levels. The circulatory system is responsible for transporting blood, oxygen, nutrients, and hormones throughout the body, but it does not regulate these functions by itself. The regulation of metabolism, growth, and development is distinctively the role of the endocrine system, making it the correct answer.