GLOSSARY

Phagocytosis is a type of endocytosis in which a cell engulfs large particles such as bacteria, dead cells, or tissue debris.
The term derives from the Greek phagein, meaning “to eat,” and it is therefore also described as cell eating.

Mechanism

The cell surrounds the particle by extending pseudopodia and encloses it in a membranous sac called a phagosome.
The phagosome then fuses with a lysosome, and lysosomal enzymes break down its contents.
The main phagocytic cells of the body are neutrophils and macrophages, which form part of the innate immune system.

Relevance to Sport

After intense exercise or muscle injury, first neutrophils and then macrophages migrate into the damaged tissue and clear away the debris of injured fibers by phagocytosis.
Besides clearing debris, macrophages secrete signaling molecules that activate satellite cells for muscle repair; this is why a short-lived inflammatory response is a normal part of recovery and adaptation.

Key Teaching Point

Phagocytosis is for large, solid particles and is usually carried out only by specialized cells, whereas pinocytosis is the uptake of fluid and dissolved molecules and occurs in almost all cells.