Infection And Immunity Notes

Infection & Immunity Pathology - the study of suffering General pathology - mechanisms and characteristics of disease processes eg inflammation, thrombus Systemic pathology - description of specific diseases affecting organs or systems eg ulcerative colitis Cellular responses to injury Cellular adaptations: atrophy, hypertrophy, hyperplasia, metaplasia Acute cell injury: non-lethal [REVERSIBLE], lethal [NECROSIS, APOPTOSIS] Chronic cell injury: sub-cellular alterations, intracellular accumulations, pathological calcification Hypoxic injury Reduction in oxygen delivery to tissue leads to ischaemic necrosis An area of ischaemic necrosis leads to an infarct by a process called infarction Eg myocardial infarction - heart attack Infective injury Infection by bacteria, viruses etc. Leads to cells necrosis Either by 1. Direct toxic injury by a product of the microorganism or 2. Immunological injury by the host's response to the microorganism Toxic injury Diverse pathways of injury Mechanical injury Cold - frostbite Heat - burns Most causes of cell death are my oxidative injury mediated by free radicals Cell death is part of normal tissue development NECROSIS Cell death from adverse EXTERNAL EVENT APOPTOSIS Cell death from 'PROGRAMMED' INTERNAL EVENT In practice three critical components of cellular function are chosen to define cell death Boundary functions Membrane integrity [structurally & functionally] is crucial to maintaining the osmotic stability of the cell Energy metabolism Membrane function is dependant on energy metabolism and loss of high energy phosphate compounds paralyses functions such as pumps Protein synthesis The half life of many cytoplasmic proteins is very short. Loss of protein synthesis ability leads to impairment of energy metabolism and membrane function Techniques for assessing cell death Dye uptake - loss of membrane function allows dye to enter freely Radiolabelling of protein - radiolabelled methionine tests protein synthetic capability Morphology - the histological appearance of cells in the tissue MECHANISMS OF CELL DEATH ATP Depletion - leads to a reduction in cell function but not structural damage Reperfusion injury - structural damage as a result of Reactive Oxygen Intermediates (ROI) during reperfusion [re-entry of oxygen to ischaemic tissue] of the hypoxic tissue by oxygen. Specifically damages lipids [C=C bonds], proteins [S=S bonds] and DNA [single strand breaks at thymine residues] Types of Necrosis Coagulation - most common, where all cytoplasmic proteins are denatured Liquefication - the action of proteolytic enzymes, converting necrotic tissue to a dfluid, typically the brain Caseous - tissue converted to a firm, dry, friable material. Seen in TB Gangrenous - tissue affected by bacterial action Apoptosis Single cell death without disruption of the local tissue architecture Programmed cell death Can be: ? Developmental o Organogernesis - deletion of interdigital webs ? Metamorphosis o Amphibia ? Endocrine tissue o Removal of trophic stimuli ? Immune system o T cell maturation ? Tumours It is an active process which becomes initiated at certain points in the cell cycle Cellular Adaptations Atrophy - reduction in size of the cell by the loss of cytoplasm. It is reversible Hypertrophy - increase in the size of cells and therefore an increase in the size of tissue Hyperplasia - increase in the number of cells in a tissue. Parallel to hypertrophy Aplasia - no growth of cells Metaplasia - a reversible change where one mature cell is replaced by another mature cell Dysplasia - deranged growth. Cells undergoing abnormal proliferation Effects of Radiation Physical transfer of energy from the site of origin to the biologic target, inducing ionization of its atoms If the energy transfer is high enough, the radiation can eject an electron orbiting around the nucleus of the atoms to produce ion pairs consisting of ejected electrons and residual positive nucleus. This is ionizing radiation Electromagnectic Radiation Energy propagated through space in the form of coupled electrical and magnetic fields X-Ray: artificially produced photons 

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