General pathology is the study of the mechanisms of disease (with emphasis on aetiology and pathogenesis), while systematic pathology is the study of diseases as they occur within particular organ systems – it involves a
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General pathology is the study of the mechanisms of disease (with emphasis on aetiology and pathogenesis), while systematic pathology is the study of diseases as they occur within particular organ systems – it involves aetiology, pathogenesis, epidemiology, macro- and microscopic appearance, specific diagnostic features, natural history and sequelae.
Academic pathology includes research and teaching, and the discipline of experimental pathology was derived from this. Clinical pathology is often referred to as laboratory medicine and includes a number of diagnostic disciplines.
Pathology provides the basis for understanding: The mechanisms of disease
The classification of diseases The diagnosis of diseases The basis of treatment
Monitoring the progress of disease Determining prognosis Understanding complications
SNOMED – standard classification of disease – considers the following aspects: Topography
Morphology Aetiology Function Disease Procedure Occupation
• Techniques of Pathology
Gross pathology – macroscopic investigation and observation of disease
Light microscopy – thin section of wax or plastic permeated tissues, snap-frozen tissues Histochemistry – microscopy of treated tissue sections (to distinguish cell components) Immunohistochemistry and immunofluorescence – tagged antibodies (monoclonal better) Electron microscopy
Biochemical techniques – e.g. fluid and electrolyte balance, serum enzymes Cell cultures – also allowing cytogenetic analysis
Medical microbiology – direct microscopy, culturing and identification
Molecular pathology – in situ hybridisation (specific genes/mRNA), polymerase chain reaction
CELL INJURY
• The Pathogenesis of Cell Injury
Normal cell structure and function requires:
Nuclear function for nucleic acid, protein, lipid and carbohydrate synthesis
Enzyme function for assembly and degradation of organelles and cell products
Membrane function for the transport of metabolites/messengers and for the ionic and fluid homeostasis
Energy production and the formation of high-energy compounds by aerobic phosphorylation (and/or anaerobic glycolysis)
Injury to the nucleus:
Genetic defects – single gene, multiple gene or whole chromosome abnormalities
Nutritional disturbances – e.g. pernicious anaemia due to B12 deficiency affecting DNA synthesis in haematopoietic cells
Toxic injury – may inhibit nuclear functions (synthesis, division)
Standard background radiation is approximately 10-3 rads, with minor consequences for dosages lower than 10 rads. A dose of 100 rads will give mild radiation sickness. A dose of 1000 rads will give severe radiation sickness, with pancytopenia. Note that UV is sufficient to create pro-mutagenic damage to DNA and hence has long-term effects.
Ataxia telangiectasia is due to a fundamental failure to repair damaged DNA. Individuals with this condition have hypersensitivity to DNA damage (e.g. radiation). Fragile X syndrome is due to an expansion in an unstable codon (6-50 in normal individuals, 250-4000 in affected individuals) which leads to susceptibility to nuclear damage.
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