In the young disc, the nucleus pulposus is a semi-fluid mucoid mass that is the remnant of the embryological notochord. It has a few scattered cartilage cells and collagen fibers. It is in essence a noncompressible fluid. It is approximately 70 to 90% water with proteoglycans forming the next major constituent. The bottle brush proteoglycans trap and hold the water within their domains. Dispersed collagen fibers make up the final major component. With increasing age, the nucleus pulposus becomes more cartilaginous and less fluid-like.