Intervertebral disc

The intervertebral disc



Though it is not strictly part of the usual diarthrodial joints, the structure of the intervertebral discs is shortly presented as its pathology is very common problem.





Two main parts of the intervertebral discs are the outer ring (annulus fibrosus) and the inner gelatinous material. (nucleus pulposus). The outer ring consists of fibrocartilage (type I collagen), while the inner material shows many similarity to the articular hyaline cartilage both in its biochemical (type II collagen) and histological appearance. The function of the outer ring would be to keep the inner substance within the disc and resist the rotational and loading forces. The inner material functions as shock absorber for axial loads. Intervertebral discs loose their water content with time and become narrower (the explanation behind the loss of height in elderly) as a normal aging process.







The tissues of the disc are hypotrophic, and consume only very little oxygen and other nutritional material. As the inner part of the disc is avascular, all molecules get to the disc by diffusion. To have an effective diffusion between the tissue layers, the diurnal rhythm  of sleeping (lying flat) and walking (up straight position) are essential as during the day a fairly large portion of the water content of the disc is leaving the disc, along with most of the waste material, during sleeping, on the other hand water is entering the disc transporting cardinal nutrition to the cells within the disc. This fact explains why one is 2-3 cm taller in the morning. Water content of the discs decreases with age (height may be 5-10 cm less in elderly people), and the herniation problems almost disappear in the older population.   


gerinc mus muris

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