these four things which are circulatory, respiratory, digestive, and excretory systems. these systems help things in our body it helps us breath and other good things like the tissue it helps us keep bad stuff from our body when we eat something bad or something we shouldn't eat thats bad for your body. each of these systems that are in our body really help us for when we eat and when we breath and other things we do. the digestive system breaks down food when you eat it breaks it down into little chunks of pieces. the excretory system is the nephrons about our blood or when we need urine. and the system is the circulatory system that delivers important materials throughout your body. blood is carried throughout your body by three kinds of blood vessels. and the last system is the respiratory system's job is to take in oxygen, which body cells need, and of get rid of carbon dioxide, a waste gas. and there are all the systems about eating our blood vessels and the blood passing through the kidneys and our body. the digestive system has the salivary glands, esophagus, liver, and pancreas, stomach, small intestine, and the large intestine. the circulatory system contains the heart, vein, and the artery and capillaries. respiratory system has nasal passages, trachea, and the lungs. the excretory system contains the kidneys, ureter, and the bladder for nephron. and those are all the systems we have.