The spinal discs lie between two vertebrae and therefore are designated as intervertebral discs. One can easily imagine these discs as pillow cushions, which have a cover of firm connective tissue in close interweaved fibrous layers. This pillow cushion is firmly connected with the under lying vertebral body.

The filling of the core through the fibrous annulus 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 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.