The Intervertebral Disc
The spinal discs lie between two vertebrae and therefore are designated as intervertebral discs. One can easily imagine these discs as very tough spacers, which have a very tough of laminated covering of firm connective tissue in close interweaved fibrous layers. This spacer is firmly connected with the vertebral bodies above and below it. To get an idea how tough the discs are, remember that power lifters can hold over 500 pounds above their heads. Every disc in the lumbar spine and most of the discs in the thoracic must be able to support that total weight to make this feat possible. This is done with very little bulging from the discs. If there was significant bulging these powerlifters would fold over in pain. The discs can also be thought of as inflated truck tires and once they begin to deflate, instability of what they are supporting begins.
The filling of the core through the fibrous annulus and its connection to the vertebrae, which supply nutrients to the disc, is an indispensable task within the moving segments.
Body weight, loading, movements and impacts on the spinal column are distributed by the spinal discs uniformly among the vertebrae. Otherwise, it would result in an overload of the vertebrae and lead to a vertebral breaks.
The jelly-like core works as a ball-and-socket joint. When bending forward, backward or side to side the jelly mass gets out of the way of the motion and extends to the expanding side and transfers the pressure and load to the firm part of the annulus.
Each spinal disc is about one-quarter as thick as the accompanying vertebrae. In long-term loads, core fluid of the vertebral discs is squeezed through the firm fiber ring into the blood and lymphatic systems, therefore the spinal disc decreases its fluid content and becomes narrower. That is especially the case during hour long sitting or while carrying heavy loads. If lying, especially during the load-free night's sleep, the spinal discs reabsorb fluid again and are filled up tightly in the morning. These processes are measurable. In the mornings we are two to three centimeters taller than evenings. Uniform release and resumption of fluids are needed for a healthy metabolism of the spinal discs and provide for the nourishment for the total spinal disk.
Increasing age causes a slow deteriorization of the intervertebral discs, like in many other tissues. Loss of disc fluid causes the discs to be of less height than when it was younger. Age is responsible for the atrophy of the spinal discs and the reason why older people are shorter than they were in their youth.