Cellular Injury and Adaptation

The clinician integrates advanced pathophysiology as the foundation for clinical reasoning across all body systems. Cellular injury progresses through reversible changes (cellular swelling from impaired Na+/K+ ATPase, endoplasmic reticulum swelling, mitochondrial dysfunction) to irreversible injury (membrane damage, lysosomal enzyme release, nuclear changes -- pyknosis, karyorrhexis, karyolysis) when the point of no return is crossed (mitochondrial permeability transition, massive calcium influx). Cell death occurs through necrosis (coagulative, liquefactive, caseous, fat, gangrenous, fibrinoid) or apoptosis (programmed cell death via intrinsic mitochondrial or extrinsic death receptor pathways activating caspase cascades). The inflammatory response involves vascular changes (arteriolar vasodilation via histamine, prostaglandins, and nitric oxide; increased permeability from endothelial contraction creating intercellular gaps), cellular events (neutrophil margination via selectins, firm adhesion via integrins, emigration through vessel walls, chemotaxis toward complement fragments and bacterial products, phagocytosis and killing via reactive oxygen species and lysosomal enzymes), and chemical mediators (vasoactive amines, arachidonic acid metabolites via COX and LOX pathways, platelet-activating factor, cytokines IL-1/IL-6/TNF-alpha, complement system, kinins). The clinician applies these principles to interpret clinical findings, predict disease progression, and select pharmacotherapy that targets specific pathophysiological mechanisms.