Another similarity is that they all eliminate waste or tell the body to eliminate waste. The skin sweats eliminating waste, and the digestive system eliminates the waste and separates it from the nutritions of the food, and the nervous system tells the body to eliminate waste.
One last similarity is that they all They all have something to do with nutrients. The skin produces vitamin D, the digestive system breaks down nutrients and uses them in the body, and the nervous system tells the body what to do with them. Now lets get back to class before Mrs. Pagnotta notices that we are missing.
Now I know what you meant by all the systems are similar and work together. Thanks for teaching me!