Pathophysiology is responsible for analyzing the abnormal functioning of organs, systems and apparatuses in order to recognize the mechanisms by which the symptoms and signs of the diseases that afflict human beings are produced, generating chemical, physical and behavioral alterations; in all cases it will have a direct relationship with morphophysiology, biochemistry, immunology and pharmacology. Historically, scholars of health-disease have tried to elucidate this internal and complex relationship of mankind; since the 5th century BC. Hippocrates classified diseases into acute and chronic in order to generate diagnoses and treatments; then in the 2nd century A.D. Galen was the first to experiment on the functioning of the human body; in the Middle Ages Muslim physicians developed research on the heart and lungs; in the 19th century research delved into cellular theory.