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Water content increases with age
10%
499/4854
Proteoglycans increase with age
16%
764/4854
Degradative enzyme activity decreases with age
470/4854
pH increase with age
787/4854
There is a conversion to fibrocartilage
48%
2307/4854
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Disc aging leads to an overall loss of water content and conversion to fibrocartilage. The intervertebral disc allows spinal motion and provides stability. In addition, it is responsible for 25% of spinal column height. It consists of an outer annulus, with a high concentration of Type I collagen, and an inner nucleus pulposus, with a high concentration in Type II collagen. With aging there is degeneration of the disc that may alter the function as well. Boos et al. investigated age-related temporospatial histologic changes in human lumbar intervertebral disc, and developed a practicable and reliable classification system for age-related histologic disc alteration. They noted clear histologic evidence for the detrimental effect of a diminished blood supply on the endplate, resulting in tissue breakdown beginning in the nucleus pulposus and starting in the second life decade. They were able to create a classification system that showed significant correlation with age and macroscopic grade of degeneration. Roberts et al. wrote a comprehensive review of vertebral disc histology and pathology. They explain that with increasing age, water is lost from the matrix of the disc, and the proteoglycan content also changes and diminishes. The disc, particularly the nucleus, becomes less gelatinous and more fibrous. They conclude that a change in the morphology of the tissue is likely to alter the physiologic and mechanical functioning of the disc. Illustration A shows an intervertebral disc and its primary components. The nucleus pulposis (primarily type II collagen) is found centrally in the disc surrounded by the annulus fibrosus (primarily type I collagen). Illustration B shows a T2-weighted lumbar MRI pointing out the normal disks with higher water content (bright on T2) and degenerated disks with less water content (dark on T2). Incorrect Answers: Answer 1: Intervertebral water content decreases with age. Answer 2: Intervertebral proteoglycans decreases with age. Answer 3: Degradative enzyme activity increases with age. Answer 4: pH decreases with age
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