Cartilages, joints, ligaments and movement

Cartilage is a connective tissue made of cartilage cells. It lies at the ends of bones, at joints and between the vertebrae, where it protects the bones from wearing away through constant rubbing. It also shapes the outer ear and the nose and forms part of the walls of the windpipe. Cartilage has no blood vessels, so its cells receive food and oxygen by diffusion from the tissue and fluid around them. There are three kinds of joint. In a fibrous joint the bones are fused by fibrous tissue and cannot move, as at the serrated edges of the skull bones, and with age the fibrous tissue can turn into bone. In a cartilaginous joint the ends of neighbouring bones are joined by cartilage and move very little, as between the vertebrae. Most joints are synovial. The touching bone ends are covered with a smooth layer of cartilage, and synovial fluid between them lets them slide with little friction; the joint is flexible and absorbs shocks. Some synovial joints, such as the elbow and the knee, move in one direction only. Others, such as the shoulder and the hip, allow movement in many directions.