Pathology
Core concepts
Pathology explains disease mechanisms and tissue changes. Know reversible versus irreversible cell injury, necrosis subtypes, apoptosis, inflammation, repair, hemodynamics, neoplasia, and immunopathology. Coagulative necrosis typifies ischemic injury except in the brain, where liquefactive necrosis occurs. Caseous necrosis is associated with tuberculosis. Inflammation involves vascular and cellular phases, mediators, and leukocyte recruitment. Repair may be regeneration or fibrosis. Neoplasia questions test benign versus malignant features, invasion, metastasis, grading, and staging. Hemodynamics includes thrombosis, embolism, infarction, edema, and shock.
Traps
Apoptosis is energy-dependent and generally noninflammatory; necrosis is pathologic and inflammatory. Metaplasia is a reversible substitution of cell types, not cancer. Dysplasia implies disordered growth but not necessarily invasion. A well-differentiated tumor can still be malignant. Transudate is protein-poor from pressure or oncotic imbalance; exudate is protein-rich from inflammation.
Worked example and rule of thumb
A myocardial infarction produces coagulative necrosis because ischemic injury denatures structural proteins and preserves tissue outlines temporarily. A cerebral infarct produces liquefactive necrosis because brain tissue is enzyme-rich and lacks strong supporting stroma. Rule: ischemic necrosis is coagulative everywhere except the brain.
Exam focus
Link mechanism to morphology. Ask what type of injury, what inflammatory cell, what mediator, and what complication.