Welcome to the PressBook for Pathophysiology for the PTA. This book is designed to guide the learner through a series of short readings, pictures, videos, and activities to help visualize and apply concepts covered in the course. This PressBook is a “work in progress” and any comments or suggestions are greatly appreciated, as the PressBook is easily corrected or changed to reflect new ideas in health care. Presently, limited chapters are included in the PressBook, but more chapters are being created so that someday soon, all body systems will be covered. For now, only the cardiovascular, pulmonary, musculoskeletal, and neurological systems are included, but expect this PressBook to continually grow and change. In the meantime, enjoy the learning.