Fig. 2.3 ). In reversible injury, cells and intracellular organelles typically become swollen because they take in water as a result of the failure of energy-dependent ion pumps in the plasma membrane, leading to an inability to maintain ionic and fluid homeostasis. In some forms of injury, degenerated organelles and lipids may accumulate inside the injured cells.
MORPHOLOGYThetwomainmorphologiccorrelatesofreversiblecellinjuryarecellularswellingandfattychange.
Fig.2.4B )iscommonlyseenincellinjuryassociatedwithincreasedpermeabilityoftheplasmamembrane.Itmaybedifficulttoappreciatewiththelightmicroscope,butitisoftenapparentatthelevelofthewholeorgan.Whenitaffectsmanycellsinanorgan,itcausespallor(asaresultofcompressionofcapillaries),increasedturgor,andanincreaseinorganweight.Microscopicexaminationmayshowsmall,clearvacuoleswithinthecytoplasm;theserepresentdistendedandpinched-offsegmentsoftheendoplasmicreticulum(ER).Thispatternofnonlethalinjuryissometimescalledhydropicchangeorvacuolardegeneration.
Fatty change ismanifestedbytheappearanceoftriglyceridecontaininglipidvacuolesinthecytoplasm.Itisprincipallyencounteredinorgansthatareinvolvedinlipidmetabolism,suchastheliver,andhenceitisdiscussedinChapter16.
Thecytoplasmofinjuredcellsalsomaybecomeredder(eosinophilic),achangethatbecomesmuchmorepronouncedwithprogressiontonecrosis(describedlater).Otherintracellularchangesassociatedwithcellinjury(
Fig.2.3 )include(1)plasmamembranealterationssuchasblebbing,blunting,ordistortionofmicrovilli,andlooseningofintercellularattachments;
Swelling of endoplasmic reticulum and mitochondria
Breakdown of plasma membrane, organelles, and nucleus; leakage of contents
Fig. 2.3 Reversiblecellinjuryandnecrosis.Theprincipalcellularalterationsthatcharacterizereversiblecellinjuryandnecrosisareillustrated.Byconvention,reversibleinjuryisconsideredtoculminateinnecrosisiftheinjuriousstimulusisnotremoved.
withdetachmentofribosomesanddissociationofpolysomes;and(4)nuclearalterations,suchasclumpingofchromatin.Thecytoplasmmaycontainso-called“myelinfigures,”whicharecollectionsofphospholipidsresemblingmyelinsheathsthatarederivedfromdamagedcellularmembranes.
In some situations, potentially injurious insults induce specific alterations in cellular organelles, such as the ER. The smooth ER is involved in the metabolism of various chemicals, and cells exposed to these chemicals show hypertrophy of the ER as an adaptive response that may have important functional consequences. For instance, many drugs, including barbiturates, which were commonly used as sedatives in the past and are still used as a treatment for some forms of epilepsy, are metabolized in the liver by the cytochrome P-450 mixed-function oxidase system found in the smooth ER. Protracted use of http://ebooksmedicine.net