joints Flashcards
what are the three classes of joints?
fibrous joints, cartilaginous joints (primary (synchondrosis) and secondary (symphysis)) and synovial joints
fibrous joints
strong fixed joints (no movement) e.g. the suture joints of the skull, teeth (the gomphosis) and the interosseous membrane between the radius and ulna which allows some rotation.
cartilaginous joints
joint surfaces covered by cartilage: primary cartilaginous joints (synchondrosis) and secondary cartilaginous joints (symphysis)
primary cartilaginous joints (synchondrosis)
strong fixed joints separated by hyaline cartilage e.g. the permanent junction in the costal cartilages and the temporary junction in the epiphyseal plates of bones.
secondary cartilaginous joints (symphysis)
strong joints which allow some limited movement composed of a fibre-cartilagenous disc which may be important in shock absorption. all found in the midline of the body (e.g. intervertebral discs, pubic symphysis)
synovial joints
most common type of joint which allow free movement.
articular cartilage
hyaline cartilage provides a low friction surface with high tensile strength in synovial joints. nourished by synovial fluid.
fibrous capsule
mainly consists of collagen. surrounds the joint to prevent destructive movement and therefore damage to joint. can thicken in areas of stress to produce ligaments. KEY FEATURE OF SYNOVIAL JOINTS.
synovial membrane
vascular connective tissue (fibrocollagenous) that lines the capsule and secretes synovial fluid to lubricate and nourish (provides oxygen and nutrients) the articular cartilage. KEY FEATURE OF SYNOVIAL JOINTS
synovial fluid
consists of hyaluronic acid, lubricin and a small number of phagocytic cells. acts to lubricate and reduce friction between articular surfaces. arrangement of glycoprotein molecules changes with energy put into it. at rest the chains of molecules are disorganised, with energy put into it the chains become aligned and therefore allow more movement. If the fluid takes a high impact blow, the fluid thickens like cornflour to prevent damage. KEY FEATURE OF SYNOVIAL JOINTS.
articular discs
(Extra feature of synovial joints) fibrocartilage structures present in between the articular surface in some joints with rotatory movements (e.g. the knee wrist, sternoclavicular joint). may have a hole in the middle allowing the synovial fluid to go between the meniscus or may not have a hole. extra structure which helps to protect the joint.
Bursae
closed sacs lined with synovial membranes and synovial fluid. found where friction occurs (between skin and bone (in the knee) and between tendons and bones in joints).
synovial sheaths
specialised bursae that surround tendons where they are subject to pressure. helps movement in a complex area (e.g. hands and feet)
what factors will influence the stability of a joint?
The shape of the joint (i.e. some synovial joint types are more stable than others - ball and socket is quite stable and hinge is less so); the strength and position of ligaments (i.e. intrinsic vs extrinsic, ligaments prevent overextension which could cause dislocation); the tone of surrounding muscles.
NB it is the surrounding structure of a joint that are most likely to be damaged with dislocation (i.e. ligaments)
osteoarthritis
a degenerative disease that is most common in weight bearing joints. the articular cartilage thins and increases the rubbing of bones together at articular surfaces. The bone therefore tries to repair itself (i.e. Wolff’s law) and bony deposits form on the articular surfaces, which further increases friction and makes it painful to move the joint. Most common form of arthritis in the UK.
