The document provides an overview of the major human body systems, including their roles and main organs. It describes the circulatory system's role in transporting substances throughout the body. It notes the excretory system filters wastes from the blood and maintains nutrient balances. The digestive system breaks down macromolecules and absorbs nutrients, with the liver serving multiple functions. The reproductive, skeletal, muscular, nervous, integumentary, endocrine, lymphatic and respiratory systems are also summarized briefly.