How does the human body work? What's a body system? What makes the human body healthy or sick? These questions and more are highlighted in this essential guide to the human body. Readers will examine different body systems, including important organs such as the brain and heart. They will learn the processes through which bodies grow, move, heal, and change. Achievable main text offers valuable inside into the biology of the human body, while fact boxes and sidebars illuminate particularly exciting information. Readers will get a deep dive into the most interesting machine in the world--the human body!