fibrill

Fibrill is a term used in biology to denote a slender, thread-like structural element that forms part of a larger tissue or cell framework. In many contexts it is synonymous with fibril, though some sources reserve fibrill for particularly fine or immature fibers. The word derives from Latin fibrilla, a diminutive of fibra, "fiber".

Fibrils occur in diverse biological contexts. In animals, collagen fibrils are the fundamental subunits of connective tissue; myofibrils in muscle cells consist of repeating filament bundles; neurofibrils (neurofilaments) provide structural support within neurons. In plants, cellulose fibrils reinforce the cell wall and influence growth and mechanics.

Structurally, fibrils are nanoscale or microscale fibers composed of protein subunits or carbohydrate polymers that assemble into larger networks. Their arrangement determines mechanical properties such as stiffness and tensile strength, and their interactions with other cellular components guide processes like transport, signaling, and tissue organization.

Pathologically, fibrillar assemblies can be involved in disease. Amyloid fibrils are insoluble protein aggregates that deposit in tissues in conditions such as Alzheimer's disease and systemic amyloidoses. Other fibrillar alterations may accompany muscular and neurodegenerative disorders.

See also: fibril, neurofibril, collagen fibril, amyloid fibril, cellulose fibril.