Intervertebral discs

A cushion-like pad between adjacent vertebrae. It is composed of an inner semifluid material (nucleus pulposus) and a hard outer ring of fibrous cartilage (the annulus fibrosus). The disc acts as a shock absorber during walking, running, and jumping. Lumbar discs are the thickest because they have to be able to resist the greatest forces. For children of up to 8 years of age, discs have a blood supply, but after that age body movements are required to mechanically pump nutrients into and wastes out of the discs. Immobility prevents the pumping action and can adversely affect disc health: regular exercise can improve it.