Agranular

Agranular is an adjective meaning lacking or deficient in granules. In biology, granules are small cytoplasmic particles or secretory vesicles that can be visible under light microscopy. When a cell or tissue is described as agranular, it has few or no such granules, in contrast to granular cells that contain conspicuous cytoplasmic granules.

In hematology, agranular leukocytes (also called agranulocytes) include lymphocytes and monocytes, which typically do not display prominent cytoplasmic granules with standard stains. This is in contrast to granulocytes—neutrophils, eosinophils, and basophils—which have noticeable cytoplasmic granules. Clinically, the term agranulocytosis denotes a severe reduction in granulocytes, especially neutrophils, with a heightened risk of infection; it is a term used to describe a condition rather than a descriptive cell type.

In neuroanatomy, agranular cortex refers to regions of the cerebral cortex that lack a well-defined granular layer IV. This contrasts with granular cortex, where layer IV is prominent, and dysgranular cortex, where the layer is present but less distinct. Examples include certain motor and limbic areas described as agranular, reflecting their characteristic cytoarchitectural patterns.

Etymology and usage: The term derives from Latin granulum, meaning “little grain.” Agranular is primarily a descriptive histological term and its precise interpretation depends on the biological context, so domain-specific conventions should be considered when applying it.