Skeletal System PDF

Cartilage: is dense connective tissue  It is semi rigid form of connective tissue that forms parts of the skeleton where more flexibility is required.  for example where the costal cartilage attach the ribs to the sternum  Articular surfaces of the bone participating in syn...

Cartilage: is dense connective tissue  It is semi rigid form of connective tissue that forms parts of the skeleton where more flexibility is required.  for example where the costal cartilage attach the ribs to the sternum  Articular surfaces of the bone participating in synovial joint are capped with articular cartilage that provides smooth , low-friction, gliding surfaces for free movement.  The cartilage is a vascular ,it obtains its nutrition by diffusion  The cartilage forms the temporary skeleton of the developing fetus but it is gradually replaced by bone The bones of the newborn are soft and flexible because they are composed mainly of cartilage  the proportion of cartilage and bone in the skeleton changes as the body grows. The cartilage remain in certain sites of the body: On the articular surfaces of most of the bones Costal cartilage  Airpassage as the nasal ,laryngeal, tracheal and broncheal cartilages External ear and Eustachian tube It is vascularised dense connective tissue composed of cells and matrix (organic : collagen fibers, inorganic : Ca, Phosph.) It is hard because of its extracellular matrix It is elastic because of the presence of organic fibers The bone exists in two forms: 1. Compact bone ( Hard bone):  it is hard, dense and forms the surface layer of all bones and the tubular shafts of long bones.  It provides strength for weight bearing.  In long bone its amount increase in the middle of the shaft.  Consists of number of cylindrical units called Haversian system  It looks like a sponge which is usually filled with red bone marrow.  It is formed of trabecullae , the lamellae are branching and anastmose with each other It is found inside the hard bone It forms the ends of long bones and the body of all other types of bones. It is a fibrous connective tissue covering the surrounding bone except at the site of articular cartilage It is very sensitive and has rich nerve supply 1. Periosteal arteries:  The main source of blood supply in all types of bones  They are derived from the nearby main vessels or from that of attached structures  They supply the outer compact bone  The bone from which the periosteum has been removed dies 2. Articular arteries:  These arteries supply the joints and the ends of the bones  Each artery divides into an epiphysial and metaphysial branches 3. Nutrient arteries:  An artery enter the bone through nutrient canal  The artery divides into proximal and distal branches in the medullary cavity of the bone  These arteries supply the bone marrow, spongy bone and deep portion of compact bone  It is the fatty vascular tissue filling the medullary cavity of the long bone and the meshes of all the cancellous bone  It concerned with the formation of blood cells  The form of the bone marrow vary with the age: 1. At birth :only red bone marrow fills all the marrow cavities of all bone 2. During childhood: yellow bone marrow replaces the red one in the distal long bones 3. In adults :the red bone marrow is only present in the meshes of spongy bones ( in the skull, vertebrae, sternum, ribs, hip, the upper end of the femur and the humerus. The medullary cavity of all the long bones contains only yellow bone marrow  Functions of skeleton Support of the body Give shape of the body Protection of soft organs Movement due to attached skeletal muscles Lever action Storage of minerals and fats Blood cell formation 1. In the length :  by continuous deposition of bone on either sides of growing plate until it ossified and fused with the diaphysis 2. In the thickness:  By sub periosteal deposition of bone by the osteoblasts forming a shaft of compact bone and marrow cavity formation by osteoclasts  Bones can be classified into five types based on shape:  Long  Short  Flat  Irregular  Sesamoid  pneumatic.cnI ,snoS & yeliW nhoJ ,2009Copyright 1. Long bones: they have long tubular shaft containing central medullary cavity and expanded articular ends (e.g. humerus, femur, metacarpals and phalanges) Short bones: they are cuboidal, they have thin cortex of compact bone with an interior completely occupied by cancellous bone. Theses bones are subjected to pressure(e.g. carpal and tarsal bone) 3. Flat bones: the internal layer of bone is enclosed between inner and outer laminae of compact bone (e.g. vault of the skull, ribs, sternum and scapula) 3. Irregular bones: have various shape (e.g. vertebrae, hip bone) Pneumatic bones: these are the bones containing air spaces ( maxilla and frontal bones) Sesamoid bones: are small bones deposited or buried in the tendons of some muscles, as patella to reduce friction on the tendon