The document discusses four human body systems - the digestive system, which breaks down food into absorbable substances; the circulatory system, consisting of the heart and blood vessels to pump and carry blood; the respiratory system including the respiratory tract and lungs for breathing; and the urinary system that expels waste from the blood through the kidneys, ureters, bladder, and urethra. The digestive system uses the digestive tract and glands for digestion. The heart pumps blood through the body via blood vessels. Breathing involves the diaphragm contracting on inhale and relaxing on exhale. Some people require dialysis if their kidneys do not function properly.