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Definition • PATHOLOGY IS THE STUDY OF THE CAUSES, MECHANISMS,PATTERNS AND EFFECTS OF ILLNESS(DISEASE) definition • study (logos) of suffering (pathos). • it is a bridging discipline involving both basic science and clinical practice and is devoted to the study of the structural and functional changes in cells, tissues, and organs that underlie disease. • By the use of molecular, microbiologic, immunologic, and morphologic techniques, pathology attempts to explain the whys and wherefores of the signs and symptoms manifested by patients while • Provides a sound foundation for rational clinical care and therapy. vital component • medical education for all – doctors, – nurses and – other health-care practitioners. Necessary • to interpret the complaints of a patient (the symptoms of disease) understand the abnormalities found on examination the signs of disease, important • be familiar with the range of abnormalities possible in an organ or tissue. Pathology is the bedrock of clinical medicine, and its study continues throughout clinical practice. Clinical symptoms • A man complains to his doctor of the sudden onset of severe, crushing, continuous central chest pain, radiating into the left side of the neck and down the left arm. • he had previously experienced similar, less severe, pain in his chest on physical exertion, but that the pain used to go away on resting. • The latest episode is associated with severe breathlessness, and the patient feels very unwell. signs • He has cold clammy skin and low blood pressure. Goal • To build up a picture of the most likely pathological processes at work, • and to work out what mechanisms are operating • and what are the causative factors • and what are the likely effects • To institute possibly life-saving, treatment Deduction • a knowledge of the range of diseases that can affect the heart, and their causes, • the doctor deduces that the patient probably has severe disease affecting his coronary arteries, which have become partially blocked by a disease process called atheroma • and that this partial blockage has resulted in the heart muscle occasionally being short of oxygenated arterial blood in periods of strenuous physical activity, leading to heart muscle pain (angina) in the past. The conclusion • most recent episode may have resulted from complete blockage of the artery, which has been made total by development of a blood clot (thrombus). • this has caused complete cessation of arterial blood supply to part of the muscular wall of the heart, and consequent death of the heart muscle cells due to loss of oxygen supply. • The doctor will make a working diagnosis of myocardial infarction. • Planning • Knowing the likely aetiology of a disease allows rational planning of investigations to confirm the clinical diagnosis. • In this instance an electrocardiogram (ECG) will show diagnostic changes, • and levels of enzymes liberated from dead heart muscle will be elevated in the blood. Institution • knowledge of the mechanisms involved (pathogenesis) also allows implementation of treatment; • in this instance administration of an agent to promote lysis of thrombus allows reperfusion of heart muscle and may limit the extent of damage. The history of chest pain which improved on rest must • mean that the coronary arteries are severely narrowed by atheroma, causing partial blockage of the lumen. • Reduction in blood supply to the heart muscle will have produced symptoms of chest pain only on exertion, when the heart is working hard and has high blood and oxygen requirements. It is characteristic that this type of pain (angina of effort) disappears on resting. The constant chest pain • must mean that the patient now has a true myocardial infarct, and that the coronary artery is completely blocked, perhaps by thrombus. the patient's life is at risk. • There will now be an area of dead heart muscle in the wall of the left ventricle, and • One must look out for symptoms and signs of the immediate complications of myocardial infarction. • It will take about 8 weeks for the infarcted heart muscle to heal by scarring; until then he is at risk. complications • This patient's immediate complications are failure of the left ventricle, leading to reduced cardiac output (responsible for his cold, clammy skin and his low blood pressure). • Also, his damaged left ventricle is unable to empty completely at systole, so there will be increased back pressure in the left atrium and pulmonary veins and capillaries. • Water will pass from the pulmonary capillary blood into his alveoli, making him very breathless (pulmonary oedema). Treatment • The breathlessness and shock must mean that the patient has a failing left ventricle. • One had better begin treatment immediately to improve the output and strength of the damaged left ventricular muscle. Pathology encompasses all aspects of disease • Special terms are used to refer to patterns, causes, mechanisms and effects of disease • Diseases can result from primary abnormalities at three levels: • Genetic function. • Physiological/biochemical function. • Gross structural arrangement of cells, tissues and organs. A limited number of tissue responses underlie all diseases • Cells and tissues respond to disease processes in a limited number of ways, • basic pathological responses. – Adaptation of cells to changes in their environment ( – What happens to cells when they cannot adapt, and how cells die – Disorders due to abnormal cell growth, for example cancer ( – Tissue responses to injury, and how tissues heal • Genetic and immune factors in disease • Adverse environmental factors that cause disease First manifestations • Frequently, the first manifestation of a disease process is not at its primary site, but takes the form of secondary effects. • To confirm or screen for disease the physician or surgeon sends samples from the patient to the pathology laboratory and asks for an appropriate analysis. diagnostic pathology laboratory medicine. • For example, in diabetes mellitus, although there is a primary abnormality in the pancreas, the diagnosis can be made by analysis of blood and urine glucose levels. • Detection and analysis of similar secondary effects are of immense value in deducing the nature and site of underlying disease processes. Diagnostic pathology/laboratory medicine • A 63-year-old man complains of increasing weakness and lethargy. • On examination he appears very pale, suggesting that he is anaemic. • The physician takes a blood sample for haematological analysis, •laboratory finding implies either inadequate iron intake, or excess blood loss. On further questioning • patient admits that he occasionally passes very dark faeces. A faecal sample is sent to the Chemical Pathology laboratory for analysis. • The patient is bleeding into his bowel, but where? Radiological examination • by barium enema suggests an abnormality in the caecum. colonoscope, • the surgeon examines the full length of the colon and finds an ulcer with raised edges at the site of radiological abnormality in the caecum. samples of tissue are taken • the edges and floor of the ulcer, and sent to the Histopathology laboratory for histological examination.