Introduction to Pathology William Osler (1849-1919) “Your practice of medicine will be as good as your understanding of PATHOLOGY” PATHOLOGY ● Origin – pathos + logos ● Definition – the study of disease; the scientific study of structure and function of the body in disease; study of suffering Includes: ● The basic structural and functional changes ● associated with disease ● The study of causes that leads to these changes ● Sequence of events that leads from structural and functional abnormalities to clinical manifestations Two Main Divisions in Pathology in the Hospital Environment 1. Clinical Pathology - involves the laboratory analysis of body fluids (such as blood, urine or cerebrospinal fluid) and bodily tissue for the diagnosis of disease. 2. Anatomic Pathology - involves the examination of surgical specimens removed from the body or sometimes the examination of the whole body (autopsy) to investigate and diagnose disease. Subdivisions of Pathology ● General Pathology – general principles of disease ● Systemic Pathology - study of diseases pertaining to the specific organs and body systems. Subspecialties of Pathology A. Histopathology – aka Anatomic Pathology, Pathologic Anatomy, Morbid Anatomy -Classic method of study -includes examination of structural changes observed by naked eye (gross or macroscopic changes) -includes examination of changes detected by light and electron microscopy supported by numerous special staining methods including histochemical and immunological techniques; 3 main subdivisions 1. Surgical Pathology 2. Forensic Pathology and Autopsy Work 3. Cytopathology Surgical Pathology - study of tissues removed from the living body via paraffin embedding techniques and frozen section Forensic Pathology and Autopsy Work - study of organs and tissues removed at postmortem for medicolegal work and for determining the underlying sequence and cause of death; “the dead teach the living” Cytopathology - includes study of cells shed off from the lesions (exfoliative cytology) and fineneedle aspiration cytology (FNAC) of superficial and deep-seated lesions for diagnosis B. Hematology – deals with diseases of the blood C. Chemical Pathology - analysis of biochemical constituents of blood, urine, semen, CSF and other body fluids D. Immunology and Immunopathology – detection of abnormalities in the immune system E. Experimental Pathology – production of disease in the experimental animal and its study F. Geographic Pathology - the study of differences in distribution of frequency and type of diseases in populations in different parts of the world G. Medical Genetics - branch of human genetics that deals with the relationship between heredity and disease. H. Molecular Pathology - the detection and diagnosis of abnormalities at the level of DNA of the cell PATHOPHYSIOLOGY ● physiology of altered health ● Combines the words pathology and physiology ● Deals not only with the cellular and organ changes that occur with disease, but with the effects that these changes have on total body function ● Focuses on the mechanisms of the underlying disease and provides the background for preventive as well as therapeutic health care measures and practices Diseases What is Disease? Disease – the opposite of health Health - Health is a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity. Health – condition when the individual is in complete accord with the surroundings Disease – loss of ease (or comfort) to the body (i.e. dis-ease) Di – an interruption, cessation or disorder in the function of a body or organ or system that is characterized usually by a recognized etiologic agent/s, an identifiable group of signs and symptoms, or consistent alterations. Disease and Illness Disease – suggests an entity with a cause Illness – reaction of the individual to disease in the form of symptoms and physical signs Syndromes – combination of symptoms caused by altered physiologic process ASPECTS OF THE DISEASE PROCESS THAT FORM THE CORE OF PATHOLOGY Etiology - the study of the cause; the causative factors in a particular disease; ‘why’ of disease Pathogenesis - mechanisms by which lesions are produced; ‘how’ of disease; sequence of cellular, molecular and biochemical events that follow the exposure of cells and tissues to an injurious event -mutated genes -function of encoded proteins -biochemical events -morphological events -still not fully understood Morphological Changes – structural alteration in cells and organs; either: - characteristic of a disease or - diagnostic of an etiologic process Functional Derangements and Clinical Manifestations – signs and symptoms, clinical course, outcome, clinicopathologic relations BASIC TERMINOLOGY OF PATHOPHYSIOLOGY DIAGNOSIS ● Assimilating the information from patient’s history, physical examination, and laboratory findings to identify the condition causing the disease. ● Also refers to the name given to the disease i.e. Diabetes, multiple sclerosis PROGNOSIS ● Predicting the likely or expected development of a disease, including whether the signs and symptoms will improve or worsen (and how quickly) or remain stable over time; MANIFESTATIONS OF DISEASE SYMPTOMS ● Evidence of disease perceived by patients i.e. pain, lump, diarrhea ● Health practitioners elicit these during an interview with the patient and record them in the patient’s chart as the history SIGNS ● Physical observations made by the person who examines the patient (i.e tenderness, a mass, abnormal heart sounds) ● Elicited and observed during the physical examination ● Results are recorded in the patient’s chart. LABORATORY FINDINGS ● - Observations made by the application of tests or special procedures X-rays, blood counts, biopsies LESIONS ● Characteristic changes in tissues and cells produced by disease in an individual and experimental animal EXOGENOUS DISEASE ● Agents causing injury acting from outside the body ENDOGENOUS DISEASE ● Acting from within the body ETIOLOGIC AGENTS ETIOLOGY – the study of the cause; the causative factors in a particular disease; ‘why’ of disease Etological Agents: ● Congenital Defects ● Inherited or Genetic Disorders Biologic agents ● Immunologic Dysfunction ● Metabolic Derangements ● Degenerative Changes ● Malignancy ● Physical forces/agents ● Chemical agents ● Nutritional excesses or deficits CONGENITAL DEFECTS ● Abnormalities of structure, function, or body metabolism that are present at birth. ● These abnormalities lead to mental or physical disabilities or are fatal. GENETIC DISORDERS ● Caused by abnormalities in the genetic makeup at the chromosomal or genetic (gene) level (inherited from parents) ● Developmental diseases develop during embryonic or fetal development ● Range of abnormalities very broad - Deformities can be preset at birth (congenital abnormalities) - Biochemical changes caused by genes but influenced by the environment can appear later on (i.e diabetes) BIOLOGIC AGENTS ● Usually classified by the type of offending organism - Bacteria - Fungi - Protozoa Viruses These are called infections and diseases caused are infectious diseases Cause cell destruction directly or toxins elaborated by infectious agents IMMUNOLOGIC DISEASES ● Caused by aberrations to the immune system ● Hypersensitivity reaction - exaggerated immune response to an antigen ● Immunodeficiency - deficiency of a component of the immune system which leads to increased susceptibility to different diseases ● Autoimmunity - abnormal (exaggerated) immune reaction against the self antigens of the host. METABOLIC DERANGEMENTS ● Disorders that stem from a deficiency in the activity of an enzyme involved in the synthesis or breakdown of intermediates in the metabolism of carbohydrates, fats or proteins. DEGENERATIVE AND INFLAMMATORY DISEASE ● Caused by forces or agents that destroy cells, or intercellular substances, deposit abnormal substances in tissues or cells, or cause the body to injure itself by means of the inflammatory process MALIGNANCY ● A disease, including but not limited to cancer, in which the progress is extremely rapid and generally threatening or resulting in death within a short time. PHYSICAL FORCES/AGENTS Direct Physical injury is called TRAUMA Physical agents causing disease include: - Heat and cold - Electricity - Atmospheric Pressure changes - Radiation (electromagnetic and particulate) CHEMICAL INJURIES ● Subdivided into the manner of injury ● Poisoning (accidental, homicidal, or suicidal) ● Drug Reactions - Toxic effects of prescription or proprietary drugs taken to treat disease) NUTRITIONAL EXCESSES OR DEFICITS ● Any of the nutrient-related diseases and conditions that cause illness in humans. They may include deficiencies or excesses in the diet, obesity and eating disorders, and chronic diseases such as cardiovascular disease, hypertension, cancer, and diabetes mellitus. NUTRITIONAL EXCESSES OR DEFICITS ● May arise as a result of poor supply, interference with absorption, inefficient transport within the body, or defective utilization CAUSES OF DISEASE IDIOPATHIC – cause of disease is unknown IATROGENIC – a treatment, a procedure or an error may cause a disease – e.g. bladder infection following catheterization, bone marrow damage caused by a prescribed drug TERATOGENIC – diseases that are caused by drugs that cross the placental barrier and harm the fetus CAUSES OF DISEASE CONTAGIOUS – transmitted by direct, intimate or by skin contact VENEREAL – transmitted by sexual contact INFECTIOUS – caused by pathogenic microorganisms COMMUNICABLE – transmitted by agents, fomites, vector or carrier ONSET OF DISEASE ACUTE – sudden and obvious onset; rapid course; e.g. gastroenteritis with vomiting, cramps, diarrhea FULMINATING – acute fatal disease CHRONIC – slow onset, long duration INSIDIOUS – gradual progression with only vague or very mild signs; e.g. hepatitis INTERCURRENT – occurs during the course of another disease DURATION OF DISEASE ACUTE – short term illness that develops very quickly with marked signs such as high fever or severe pain; e.g. acute appendicitis CHRONIC – milder condition developing gradually, but persists for a long time and usually causes more permanent tissue damage; e.g. rheumatoid arthritis NATURAL HISTORY OF DISEASE ● The natural history of a disease refers to the course of a disease in an individual, from onset to resolution, in the absence of intervention. ● The evolution of a disease in a population over time, in the absence of intervention. ● There are four main stages in the natural history of a disease: - Susceptibility stage -Sub-clinical stage - Clinical stage - Recovery, disability or death STAGE OF SUSCEPTIBILITY Disease has not developed, but risk factors are present. ● E.g. Coronary Heart Disease Risk factors – smoking, hypertension, high serum cholesterol level STAGE OF SUSCEPTIBILITY ● Predisposing factors – encompass the tendencies that promote development of a disease in an individual; indicates a high risk for the disease but not certain development ● Precipitating factor – a condition that triggers an acute episode E.g. a patient may be predisposed to coronary artery disease and angina because of a high cholesterol diet. An angina attack can be precipitated by shoveling snow on a very cold day STAGE OF PRESYMPTOMATIC DISEASE (SUB-CLINICAL) ● Pathologic changes occur, but no obvious manifestations are exhibited by the patient because of the great capacity of some organs ● Rely on laboratory, radiographic or other screening methods to detect pathologic changes ● For infectious diseases – known as the incubation period ● For chronic diseases – known as latency period ● Period may be brief as seconds (hypersensitivity and toxic reactions) or long as decades (chronic diseases) THE PRODROMAL PERIOD ● Comprises the time in the early development of a disease when one is aware of a change in the body, but the signs are nonspecific ● E.g. Fatigue, loss of appetite, headache ● Laboratory tests are negative during the prodromal period; thus it is difficult to confirm a diagnosis STAGE OF CLINICAL DISEASE ● Sufficient end-organ changes have occurred, so there are recognizable signs and symptoms to disease PATIENT – the person affected by disease STAGE OF RECOVERY, DISABILITY, DEATH ● Some diseases run their course and then resolve completely with or without treatment. ● Some cause disability ● Disability – any temporary or long-term reduction of a person’s activity as a result of an acute or chronic condition; note emphasis on loss of function rather than on structural defect ● Remissions – manifestations of disease subside ● Exacerbation – sudden increase in the severity or seriousness of the signs and symptoms during the course of disease STAGE OF RECOVERY, DISABILITY, DEATH ● Complications – unfavorable conditions that arise during the course of a disease; new or secondary additional problems that arise after the original disease begins, e.g. congestive heart failure after a heart attack ● Sequelae – remote after effects produced by a disease; the potential unwanted outcomes of the primary condition, e.g. paralysis following recovery from stroke ● Convalescence or rehabilitation – period of recovery and return to the normal healthy state; may last for several days or months DEATH - the cessation of life; permanent cessation of vital functions ● Legal and medical – irreversible cessation of all of the following: - Total cerebral function (flat line in EEG) - Spontaneous function of the respiratory system -Spontaneous function of the circulatory system
