Which sequence correctly lists the four steps to the orthopedic injury model?

• A. Leukocytes approaches bacteria, leukocytes engulf bacteria, leukocytes join phagosome to form phagolysosome, leukocyte digest bacteria
• B. Leukocytes engulf bacteria, leukocytes digest bacteria, leukocytes approach bacteria, leukocytes join phagosome to form phagolysosome
• C. Leukocytes digest bacteria, leukocytes approach bacteria, leukocytes join phagosome to form phagolysosome, leukocytes engulf bacteria
• D. Bacteria invade tissue, leukocytes arrive, phagolysosome forms, bacteria die

Answer: (A)

The sequence shows the order of events in the inflammatory/phagocytic response to injury: leukocytes move toward the invading bacteria, then they engulf (phagocytose) the bacteria, the phagosome forms and fuses with a lysosome to become a phagolysosome, and finally the bacteria are digested inside that phagolysosome. This progression—approach, engulf, phagolysosome formation, digestion—is logical because digestion can only occur after the bacteria have been internalized and the phagolysosome is formed with lysosomal enzymes. The option that follows this order is the best choice. The other sequences mix the steps (for example, digestion occurring before phagolysosome formation or engulfment), which doesn’t reflect how phagocytosis and intracellular digestion operate.