Body cavities are spaces within the body that house and protect vital organs. The main cavities include the thoracic cavity, which contains the heart and lungs, and the abdominal cavity, which holds organs like the stomach and intestines. These cavities are lined with membranes that help reduce friction as organs move. Another important cavity is the pelvic cavity, which contains the bladder and reproductive organs. Each cavity is separated by structures like the diaphragm and pelvic bones, ensuring that organs are organized and function properly. Understanding body cavities is essential for studying human anatomy and health.