5.3K views · 350 reactions | What is appendicitis? The appendix is a thin tube that is joined to the large intestine. It sits in the lower right part of your belly (abdomen). When you are a young child, your appendix is a working part of your immune system, which helps your body to fight disease. When you are older, your appendix stops doing this and other parts of your body keep helping to fight infection. | Karen Society of Nebraska | Facebook