What you’ll learn to do: Describe the circulatory, immune, respiratory, and digestive systems

This set of body systems has been grouped together as the “cell maintenance systems.” Remember, this isn’t a hard-and-fast categorization: these systems are grouped together to help you organize your learning. These body systems all function to maintain the cells in your body: the circulatory, respiratory, and digestive systems provide the nutrients and energy your cells need to live. The immune system protects these cells from pathogens.