Week 1

Introduction to Pathology

Dr.İ.Taci Cangül


What is Pathology?

• “Scientific study of disease" or the alterations that occur when abnormal influences ( bacteria, viruses, etc.

) affect cells, tissues, or body systems. More specifically, pathology may be defined as the "scientific study of the molecular, cellular, tissue, or organ system response to injurious agents or adverse influences."

Pathology Deals with …

• The causes of disease (etiology)

• Mechanisms of disease (pathogenesis)

• Structural alterations of cells and tissues

• Functional alteration and consequences of disease

Function of Pathology

Pathology serves as a "bridge" or "link" between the preclinical subjects

( anatomy, physiology, etc .) and the courses in clinical medicine. Actually, pathology provides a logical means of relating the knowledge of normal structure and function ( anatomy and physiology ) to abnormal structure and function as encountered in a diseased animal.

Basic Language of Pathology

In order for a subject or course to be meaningful, one should become familiar with the basic terminology applicable to that subject.


• “State in which an individual is living in complete harmony with his environment"

• A relative state

• All body functions are performed normally even though lesions may be present in organs and/or tissues. It should be remembered that the transitional zone between health and disease is difficult to define


• “State in which an individual exhibits an anatomical, physiological, or biochemical deviation from the normal.

The term "disease" is employed to describe a state in which there is sufficient departure from the normal for clinical signs or symptoms to be produced.


• “Structural or morphological alterations associated with a diseased state in an individual”

• Gross lesion : Naked-eye

• Microscopic lesion : Light microscope

• Ultrastructural lesion : Electron microscope

• Pathognomonic Lesion: A change which is specifically characteristic of a disease. When one sees a pathognomonic lesion, he knows that a particular disease is present.


• “Study of the cause of a disease"

• An etiologic agent is the factor ( bacterium, virus, etc.

) responsible for lesions or a disease state.

• Predisposing Causes of Disease : Factors which make an individual more susceptible to a disease ( damp weather, poor ventilation, etc.


• Exciting Causes of Disease : Factors which are directly responsible for a disease (bacteria, viruses, hypoxia, chemical agents, etc .).

Clinical Signs

• “Functional evidence of disease which can be determined objectively or by the observer" ( lameness, salivation, increased respiratory efforts, etc.

) ”

• Clinical signs are seen only in the living individual.


• “Determination of the nature of a disease"

• A morphologic or anatomic diagnosis is based on the location and nature of the lesion

(hemorrhagic enteritis, etc.) . Etiologic diagnosis is made on the basis of the cause

(dirofilariasis, etc.) . Definitive diagnosis is made on the basis of the specific disease entity involved ( canine distemper, etc.).

A clinical diagnosis is made on the basis of clinical signs observed in the living animal.


• Probable outcome of a disease in a living individual. It is the clinician's estimate of the severity and possible result of a disease.


• “Progressive development (sequence of events) of a disease from the time it is initiated to its final conclusion in recovery or death”

• Necropsy: Gross examination of the carcass by systematic dissection in order to evaluate any abnormal changes

(lesions) that may be present

• Autopsy: Synonymous to necropsy in human medicine

• Biopsy: Removal and examination of tissue obtained from the living body

• Euthanasia: Intentional putting to death of an individual with an incurable or painful disease by employing humane means

• Somatic death: Death of the entire body

• Necrobiosis: Death of cells at the end of their normal life-span within the living body

(epithelial cells of the skin, leukocytes, etc.)

• Necrosis: Morphological changes caused by the progressive degradative action of enzymes on the lethally injured cell within the living body

Postmortem Changes

• Cell death which accompanies or occurs after death of the entire body ( somatic death)

• Postmortem autolysis: Self-digestion by enzymes

• Postmortem putrefaction: Decomposition of tissues by bacterial enzymes after death of the entire body

• Rigor mortis: Stiffening of all muscles after death

Branches of Pathology

• General Pathology

• Systemic Pathology

• Gross Pathology

• Cellular Pathology

• Surgical Pathology

• Clinical Pathology

• Immunopathology