Glucosamine and chondroitin are two molecules that make up the cartilage found within joints. Inside your joints, the cartilage undergoes a constant process of breakdown and repair. However, to be properly repaired and restored, the building blocks of cartilage must be present and available, together with plenty of oxygen and no doubt a myriad of other vitamins/minerals, enzymes, hormones, amino acids. The principle behind the use of glucosamine/chondroitin supplements is that more of the cartilage building blocks will be available for cartilage repair.
Glucosamine is sugar found naturally in the bones, bone marrow and cartilage of animals. That means it is found in our bodies too. Glucosamine is an important precursor in the body for the manufacture of substances called Glycosaminoglycans which link to proteins to form proteoglycans which are a major component of joint cartilage. The beauty of these substances, due to their polar nature, is their ability to bind water (which is also polar), which is strongly attracted to the proteoglycans. Water, like all liquids, is incompressible giving cartilage its stiff, yet flexible properties. This makes it the perfect material for example from which to build the discs between vertebrae. So when you jump up and down, the water-filled, incompressible disc prevents the bone above from crushing the one below. The first sign on MRI that the cartilage is degenerating is loss of this water-carrying capacity. A healthy water-filled disc looks white on a scan. As cartilage degenerates, it loses this whiteness.
Chondroitin sulfate too is a glycosaminoglycan sugar making up a different important component of cartilage, particularly giving it much of its resilience to compression. It also reputedly reduces the effect of destructive and noxious chemicals on cartilage. An important component thus of cartilage.
There are many different types of cartilage in the body, so the mix of these subsances (Glucosamine and Chondroitin) will vary from one to another. For example the cartilage in the joints between the ribs and the breastbone is different to the ‘hyaline’ cartilage that lines the ends of your long bones (i.e. in the hip)