Structure And Function Of Joints

2. Structure And Function Of Joints

The joints allow controlled and almost frictionless movement. The human skeletal system (the bones and joints) provide structural support and protection to vital parts, yet allow sufficient directed movement for the functions of locomotion and the ability to grasp or seize objects.

The joint space, articular cartilage, and synovial membrane allow the wide ranges of motion necessary for these functions. The synovial joints comprise the majority of the body’s moveable joints. On each end of the bones near a joint there is a thin plate of dense bone. Tightly attached to these bony plates are the hyaline articular cartilages. These are specialized structures made up of connective tissue that acts as the bearing and gliding surfaces of the joints. In the joint cavity there is a space that contains the synovial fluid. The ligaments and muscles around the joint offer support for the joint. Normal synovial fluid is clear, pale yellow, and viscous. It is normally present in very small amounts. One to four milliliters is found in the human knee, and less in smaller joints. Its purpose is lubrication of the joint. The synovial membrane surrounds the weight-bearing cartilage and secretes the synovial fluid. The synovial tissue does not have a structural barrier between its blood vessel space. Therefore, substances from the blood are easily carried directly into the joint fluid. All of the many impurities that circulate in the blood at various times due to toxins arising from fermentation or putrefaction of food in the stomach due to improper food or combinations of food; food additives and chemicals; or uneliminated metabolic wastes, may pass directly into the joints from the blood. Once inside the joints, these substances may precipitate arthritis by irritating the inner lining of the joints.

Proper lubrication is vital to the function of the joints since it serves to keep the opposing cartilage surfaces from touching each other. If the cartilage surfaces touch, immediate destruction begins.

The lubrication fluid must also have the right chemical makeup. The fluid consists of large and small molecules which change constantly in their concentrations. As weight is put on the joint, the smaller molecules are pushed into the cartilage leaving behind the larger molecules of hyaluronic acid to bear the weight and to keep the cartilage surfaces from touching.

A molecule consisting of carbohydrate and protein is responsible primarily for joint lubrication. In the cartilage, the protein structure is the critical component of these molecules since its digestion by enzymes called proteases results in an “uncoupling” of the proteoglycan (combination of protein and carbohydrate) from the cartilage and its subsequent loss. This loss from the cartilage results in a stiffer material and is more easily damaged by wear and tear. These proteases are activated at acid pH.

Anything that tends to make the joints more acid will cause an increased rate of destruction by speeding the removal of the proteoglycans from the cartilage. Lack of exercise, eating refined foods or sugar and meats tend to make the joints more acid.