Pathology an Introduction By Dr. Hemn Hassan Othman, PhD, Histpathology Fall-2016

Pathology The term “pathology” is derived from the Greek words pathos which means diseases and logos which means study, thus pathology is a branch of biological sciences that deals with the study of all structural and functional abnormalities (at the level of cells, tissues, organs and body fluids) that take place as a result of a disease. Pathology is considered a vital link between basic sciences (anatomy, physiology, biochemistry, pharmacology…….etc) and clinical sciences (internal medicine, surgery, neurology, dermatology, theriogenology……….etc).

Historical View The understanding of histopathology started when a German scientist, Rudolf Virchow (1821-1902) from the University of Berlin, started to cut thin sections of diseased tissues with a razor blade and examined them using the microscope.

Professional divisions of pathology: Pathology includes two major professional divisions: 1. Medical pathology which deals with the study of diseases in humans. 2. Comparative pathology which deals with the study of diseases in all animal species as well as human diseases.

Academic divisions of pathology In academic studies, pathology (medical or comparative “veterinary”) is divided into two major divisions: 1. Anatomic pathology which deals with the study of the disease effects in cells, tissues and organs. 2. Clinical pathology which deals with the study of the disease effects in body fluids and secretions (blood, urine, milk…… etc.) using certain laboratory methods.

Branches of Anatomic Pathology 1. General pathology which deals with the study of the common basic changes in all tissues as a result of a disease, e.g., cell injury, necrosis, inflammation and neoplasm. 2. Systemic pathology which deals with the study of morphological changes in tissues and organs of a particular system as a result of a disease e. g., pathology of respiratory system, pathology of digestive system, pathology of nervous system…etc. 3. Special pathology which deals with the application of the basic changes learned in general pathology to the various specific diseases e.g Diabetes, atherosclerosis etc.

4. Diagnostic Pathology (Histopathology) which deals with the study of tissue abnormalities using gross and microscopic examination of biopsy samples. Biopsy: The biopsy is a tissue sample obtained surgically from a living body in order to be examined grossly and microscopically (by a pathologist) to help in establishing the diagnosis. 5. Cytopathology which deals with the study of cellular changes. 6. Surgical Pathology which refers to histopathological examination of biopsy samples surgically removed from living bodies. 7. Post-mortem pathology which deals with pathological examination of an animal or human cadaver (carcass) after death. It is also known as autopsy or necropsy.

8. Forensic pathology: It is the subspecialty of pathology that focuses on the medico-legal investigation of the cause of a sudden or unexpected death by examination of a dead body. The term forensics is derived from the Latin word forēnsis which means forum (law court). 9. Physiological pathology which deals with the study of alterations in the functions of organs and systems of the body as a result to a disease. It is also known as pathophysiology; e.g., pathophysiology of indigestion, diarrhea, abortion…..etc. 10. Immunopathology which deals with the study of diseases mediated by immune reactions. Such as immunodeficiency diseases, autoimmune diseases and hypersensitivity reactions. 11. Molecular pathology which deals with the study of alterations that take place at the molecular level (e.g., DNA damage) as a result to a disease.

12. Experimental pathology: It is the study of diseases that have been created or induced experimentally to analyze the structural & functional abnormalities in tissue to better understand the mechanism of underline diseases. Usually laboratory animals used in experimental pathology (Rabbits, Rats, Mice….ect. Illness: It means that the individual is sick, means some part of the body is not functioning properly. But some disease conditions not companied by a clinical illness means perfectly healthy e.g. stroke & heart attack.

Disease and Disease Circumstances The disease is a condition in which an individual shows a morphological, biochemical and/or physiological deviation from the normal status . Etiology The term etiology refers to the science that deals with the causes or origin of the disease. Lesions The term “lesions” refers to abnormal (pathological) structural and functional changes that occur in body during a particular disease. This word is perhaps the most commonly used word in pathology.

Macroscopical (gross) lesions: Abnormality in the tissue can be described grossly or by the naked eye including location, color, size, shape, consistency & appearance of the cut surface. Microscopical lesions: Abnormal morphological changes described under the microscope, lesions need quantification by using some general terms like mild, moderate, or severe.

Hepatic Metastatic Tumor

Pathogenesis Pathogenicity It is defined as the step by step developmental process from the beginning of the disease to its termination, or the mechanism by which the disease is developed. Pathogenicity The term pathogenicity refers to the ability of a pathogen (usually microbial pathogens) to cause disease, e.g.: 1. The highly pathogenic influenza A virus subtype H5N1 which has caused serious disease outbreaks in poultry and human. 2. The nonpathogenic strains of Escherichia coli (E. coli) which live naturally in the large intestine of human and do not cause disease.

Symptom Sign Diagnosis Prognosis The term symptom refers to any evidence of a disease as told by the patient (in case of human being). Sign The term sign refers to any evidence of a disease detectable to a clinician (can be observed by the clinician). Diagnosis The term diagnosis refers to the art or act of identifying a particular disease from its signs and symptoms. Prognosis It is the prediction of the probable outcome of a disease.

There are four possible outcomes of disease: 1. Healing and recovery 2. Functional insufficiency (Functional shortage) 3. Death 4. Impasse: An impasse is that steady (stable) state where the pathological agent cannot induce sufficient damage to cause functional impairment or death, at the same time the body cannot eliminate that pathological agent (No complete healing). An example of impasse is the carrier states in human where a disease is present in a subclinical manner (i.e., no observable signs and symptoms of the disease are present) such as the carrier states of salmonellosis in human.

Pathological process The pathological process consists of the following: 1. Injury (damage) created by the causative agent (virus, bacteria, poison, hypertension ….etc) on cells, tissues and organs. 2. Reactive changes (pathological changes) against the injury, for example, in cases of systemic hypertension there is myocardial hypertrophy of the left heart ventricle due to increase in the resistance to blood flow through the arterioles.

In summary: 1/ Pathology is the study of what happened & how, the lesion is what & the sequence of events from the point of which the lesion began through its entire development (pathogenesis) is how. 2/ It is necessary to know the pathogenesis of lesions in order to make a rational judgment for treatment, control & prevention of diseases.