Annulus fibrosus disci intervertebralis
|Annulus fibrosus disci intervertebralis|
|Cervical vertebra with intervertebral disc. (Disc annulus labeled at bottom right, and is visible at center in blue.)|
|Stages of Spinal Disc Herniation|
|Latin||Annulus fibrosus disci intervertebralis|
|Gray's||subject #72 289|
Each intervertebral fibrocartilage is composed, at its circumference, of laminæ of fibrous tissue and fibrocartilage, forming the annulus fibrosus. The lamellae are stiff and sustain compressive loads. The stiffness of the annulus works in concert with the gel-like nucleus pulposus to equalise pressure across the disc. This prevents development of stress concentrations which could cause damage to the underlying vertebrae or vertebral endplates.
The annulus consists of both type I and type II collagen - the concentration of type I collagen increasing towards the periphery of the annulus and type II collagen conversely increasing towards the centre of the disc. The higher concentrations of type I collagen in the outer annulus confers greater tensile strength.
Both "anulus" and "annulus" are acceptable spellings. Gray's Anatomy uses "annulus fibrosus," Terminologia Anatomica uses "anulus fibrosus," and Nomina Anatomica uses both forms. Etymologically speaking, anulus seems to be the correct spelling as it is the diminutive of L. anus, a ring, hence anulus, a little ring.
"Fibrosus" has no correct alternative spelling; "fibrosis" has a different meaning and is incorrect in this context. 
- Fardon DF (2001). "Nomenclature and classification of lumbar disc pathology". Spine 26 (5): 461–2. doi:10.1097/00007632-200103010-00007. PMID 11242371.
- Annulus_fibrosus at the Duke University Health System's Orthopedics program
- anulus+fibrosus+of+intervertebral+disc at eMedicine Dictionary
- Diagram at upenn.edu
- Diagram at spineuniverse.com
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