The document discusses natural death and sudden death. Natural death is defined as death caused by natural disease without trauma or poisoning. Sudden death is defined as death within 24 hours of onset of a terminal illness. The document then discusses cases of sudden death and lists the most common anatomical systems involved, including cardiovascular (45-50%), respiratory (15-23%), central nervous (10-18%), gastrointestinal (6-8%), and others (5-10%). It provides examples of conditions that could cause sudden death within each system.