The joints, or articulations, of the body allow a range of movement and mobility. There are a variety of joints in the body such as diarthrodial or synovial joints, ball and socket joints, hinge joints and fibrous joints. Each joint is composed of similar structures that give it a defined range of motion and restrict excessive movement. Two or more bones must come together to form a joint and other structures such as cartilage, tendons, ligaments and muscles support it. Structures such as synovial fluid and bursa sacs lubricate the joint to facilitate movement. Most human joints are complex and have several parts that keep them healthy, stable and functioning normally.
Bones
Bones are the primary structures of joints; two or more bones come together where normal movement is essential. The Yale-New Haven Teachers Institute notes that bones are a type of connective tissue composed of cells, extracellular matrix and minerals. It is a composite of both organic and inorganic substances such as the protein collagen, calcium phosphate, potassium, magnesium and chlorine. Calcium phosphate is the most common compound in the skeleton.
Ligaments
Ligaments are tough, elastic tissues formed of bundles of collagen. The University of Leeds explains that ligaments help to bind the bones of the joint together while still allowing motion and mobility.
Tendons
The tendons are tough, pliable connective tissues that are not elastic. They join muscles with other structures such as bone and cartilage to support and stabilize the joint while allowing movement.
Cartilage
Cartilage is a hard but elastic tissue that connects and supports the bones of the joints. There are two forms of cartilage: hyaline and articular. The second type is found in such joints as in the knee. Cartilage helps to support and facilitate movement at these articulations by covering the sliding surface to reduce friction between the bones. According to the Yale-New Haven Teachers Institute, articular cartilage is found at sites of articulation like the knee and help with the support and form of the body.
Bursa
Bursa are fluid-filled sacs that are located at the interface between the two moving bones or between a bone and another joint structure such as a tendon or ligament. The two types of bursa are called subcutaneous and synovial. They help to lubricate and decrease friction in the moving joint. Along with the cartilage, the bursa sacs act as shock absorbers to cushion the impact on the joints.
