Granule

Definition

A discrete, membrane-bound or aggregated submicroscopic particle within a cell, typically containing stored material such as proteins, enzymes, pigments, or antimicrobial compounds; in arthropods, granules are characteristic of specific hemocyte types (e.g., granulocytes), secretory cells, and sensory structures.

Etymology

From Latin granulum, diminutive of granum (grain)

Example

In the hemolymph of Lepidoptera, granulocytes contain prominent cytoplasmic granules that store prophenoloxidase and are released during encapsulation responses against parasitoid eggs.

Synonyms

• Inclusion body
• vesicle (when membrane-bound)

Related Terms

• Granulocyte
• hemocyte
• cytoplasmic inclusion
• secretory vesicle
• pigment granule
• azurophilic granule
• chromaffin granule

Usage Notes

Distinguished from larger 'granular' surface textures in exoskeletons or eggshells, which are macroscopic. In insect pathology, 'granule' also refers to the proteinaceous occlusion bodies of granuloviruses (family Baculoviridae), a distinct usage that should be specified contextually. Plural 'granules' is standard; singular 'granule' refers to an individual particle.