General Pathology: Inflammation, Repair, Regeneration, and Wound Healing
Acute inflammation
Understand the vascular and cellular phases. Vasodilatation and increased permeability (endothelial contraction, direct injury, leukocyte-mediated injury, transcytosis) produce exudate. Neutrophils marginate, roll (selectins), adhere (integrins, ICAM-1), transmigrate, and migrate along chemotactic gradients (C5a, LTB4, IL-8, bacterial peptides). Recognise the cardinal signs and their mechanisms: rubor and calor from vasodilatation, tumour from exudate, dolor from bradykinin and prostaglandins, functio laesa.
Mediators and chronic inflammation
Know the roles of histamine (mast cells), prostaglandins (COX), leukotrienes (5-lipoxygenase), platelet-activating factor, cytokines (TNF, IL-1, IL-6), and the complement cascade. Chronic inflammation features mononuclear infiltrate (macrophages, lymphocytes, plasma cells), tissue destruction, and repair attempts. Granulomas are collections of activated macrophages (epithelioid cells) with giant cells; distinguish caseating (tuberculosis) from non-caseating (sarcoidosis, Crohn disease, foreign body).
Outcomes and repair
Outcomes are resolution, suppuration, fibrosis, or chronicity. Regeneration requires preserved tissue architecture and proliferative capacity; labile tissues (skin, gut) regenerate readily, stable tissues (liver, kidney) regenerate from quiescence, permanent tissues (neurons, cardiac myocytes) heal by scar. Granulation tissue comprises proliferating capillaries, fibroblasts, and inflammatory cells. Wound healing by first versus second intention differs in clot size, contraction, and scar bulk.
Traps
Do not confuse transudate (low protein, hydrostatic/osmotic cause) with exudate (high protein, inflammation). Questions may ask which cell predominates at a given time: neutrophils early, macrophages by 24–48 hours. Myofibroblasts drive contraction, not collagen deposition alone. Vitamin C deficiency impairs hydroxylation of proline and lysine, causing defective cross-linking.
Rule of thumb
Match the mediator to its source and effect: histamine = immediate vasodilatation; prostaglandins = pain and fever; leukotrienes = chemotaxis and bronchoconstriction; TNF = systemic effects and endothelial activation.