The body is a fortress under constant assault. It faces threats from infectious diseases, parasites, allergens, environmental toxins, physical trauma, and natural disasters from without, to overzealous allergic, immune, and inflammatory responses, and cellular mutations from within. This course is an introduction to the field of pathophysiology--the study of the disruptions in a normal body's functions caused by disease or injury. Beginning with an exploration of the function of cells and common forms of injury to them, the course then proceeds through examinations of inflammatory and immune responses, infectious diseases, shock, cancer, and wound healing. These lectures provide a viewer with tools to understand diseases and injuries and the body's reaction to them.