The intervertebral discs are complex fibrocartilaginous structures that link two adjacent vertebrae. They function as cushions and are the main shock absorbents in the spine. The intervertebral discs are found from the axis (C2) to the sacrum. Overall, the spine has 23 intervertebral discs, and they form around one-third of its total length.

The thickness of an intervertebral disc varies depending on its location in the spine and within the individual disc. The thickness of the discs increases towards the sacrum, while their diameter usually corresponds to the diameter of adjacent vertebrae.

The intervertebral disc is composed of three parts:

Annulus fibrosus - the outer ring-shaped portion that is made of fibrous connective tissue; it contains great amounts of collagen fibers that are organized into many though lamellar fibers that further form a series of concentric rings called laminae, providing multi-directional support for the nucleus pulposus; the structure of the annulus fibrosus provides strength and flexibility to the intervertebral discs;
Nucleus pulposus - the inner gel-like core structure; does not receive nerve or blood supply;
Cartilaginous endplate (2) - a thin cartilaginous plate that serves as a transition structure at the interface between the vertebral body and intervertebral disc; it is composed of both fibrocartilage and hyaline cartilage.

Fun fact: A person is taller in the morning than at night. The intervertebral discs contain high amounts of water (70 - 90%). The water content changes throughout the day depending on the activity. When a person is sleeping, the nucleus pulposus rehydrates, meaning it becomes larger again and therefore causes the intervertebral disc to slightly increase in size.

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Intervertebral discs