Think of this lesson as the table of contents for our entire study of the human body. Before we dive deep into any single system, we need to see the big picture — how the body is organized from its tiniest building blocks all the way up to the complete, living organism.

By the end of this lesson you will be able to:

• List the five main levels of organization in the human body, from simplest to most complex.
• Give an example that runs through all five levels.
• Name each major organ system and state its primary function.
• Explain why all organ systems must work together to keep you alive.