Inflammation
Also known as: inflammatory response
Inflammation is the body's protective response of vascularized tissue to injury or infection, marked by redness, heat, swelling, pain, and loss of function. It delivers immune cells and mediators to the damaged site and initiates healing.
Inflammation is the coordinated response of vascularized tissue to harmful stimuli such as pathogens, physical injury, chemicals, or dying cells. Its purpose is protective: to eliminate the cause of injury, clear damaged tissue, and set the stage for repair. The classic cardinal signs — rubor (redness), calor (heat), tumor (swelling), dolor (pain), and functio laesa (loss of function) — follow directly from its vascular events.
Acute inflammation unfolds in a predictable sequence. Injured tissue and resident cells release mediators such as histamine, prostaglandins, and cytokines. Local blood vessels dilate and become more permeable, increasing blood flow (redness and heat) and allowing protein-rich fluid to leak into the tissue (swelling, which contributes to pain). Neutrophils marginate along vessel walls, adhere, migrate into the tissue, and phagocytose invaders and debris.
The outcome, or fate, of acute inflammation varies: complete resolution with restoration of normal tissue, healing with fibrosis and scarring, abscess formation, or progression to chronic inflammation. Chronic inflammation is dominated by macrophages and lymphocytes rather than neutrophils, features simultaneous tissue destruction and attempted repair, and underlies diseases from rheumatoid arthritis and atherosclerosis to tendinopathies that limit function and mobility.
Inflammation is tested across the health professions. The USMLE Step 1 exam covers its mediators, vascular and cellular events, and outcomes in general pathology, while the NPTE-PT and NPTE-PTA exams apply the stages of inflammation and tissue healing to musculoskeletal conditions and the timing of rehabilitation interventions.
Key takeaways
- Inflammation is the vascular and cellular response of living tissue to injury or infection.
- The five cardinal signs are redness, heat, swelling, pain, and loss of function.
- Acute inflammation features vasodilation, increased vascular permeability, and neutrophil migration.
- Outcomes include resolution, fibrosis, abscess formation, or chronic inflammation dominated by macrophages.
- USMLE Step 1 tests the mechanisms and fates of inflammation; the NPTE exams apply healing stages to rehabilitation.