Final answer:
Phagocytosis is the immune system's process of engulfing and digesting large particles, like pathogens, using phagocytic cells, such as neutrophils and macrophages, to protect the body from infection.
Step-by-step explanation:
Phagocytosis is a process used by certain cells to engulf and digest large particles, such as microorganisms and cellular debris. This is a form of endocytosis where the cell membrane extends around the particle to form a phagosome, which is then internalized.
Phagocytic cells, like neutrophils and macrophages, are crucial components of the immune system. Upon recognizing the invaders, phagocytes engulf them into a phagosome, which later merges with a lysosome to form a phagolysosome. Within the phagolysosome, the pathogen is killed and digested by lysosomal enzymes, and the undigested materials are expelled from the cell.
Phagocytosis should not be confused with the movement of erythrocytes through the capillary wall or the shift of fluid and protein out of capillaries, as those are different physiological processes. Phagocytosis specifically refers to the cellular ingestion and digestion of solid particles and plays a pivotal role in defending the body against infection.