Introduction to Human Skeletal System:
Skeletal system is the system of bones, associated cartilages and joints of human body. Together these structures form the human skeleton. Skeleton can be defined as the hard framework of human body around which the entire body is built. Almost all the hard parts of human body are components of human skeletal system. Joints are very important because they make the hard and rigid skeleton allow different types of movements at different locations. If the skeleton were without joints, no movement would have taken place and the significance of human body; no more than a stone.
BONE
What is a bone?
Bone is a dense type of connective tissue impregnated with inorganic salts mainly the salts of calcium
Sesamoid Bones
Sesamoid bones are usually short or irregular bones, imbedded in a tendon. The most obvious example of this is the Patella (knee cap) which sits within the Patella or Quadriceps tendon. Other sesamoid bones are the Pisiform (smallest of the Carpals) and the two small bones at the base of the 1st Metatarsal. Sesamoid bones are usually present in a tendon where it passes over a joint which serves to protect the tendon.
CARTILAGE
Cartilage is a type of connective tissue composed of special cells known as chondrocytes along with collagen or yellow elastic fibers. The fibers and the cells are embedded in a firm gel like matrix rich in mucopolysaccharides. Cartilage is not as hard and rigid as bone. It is much more flexible and elastic.
Characteristic features of cartilage: * Cartilage has no blood vessels or lymphatics and the nutrition of the cells diffuses through the matrix. This explains the slowness of healing process in cartilages. * Cartilage has no nerves and therefore it is insensitive. * Cartilage is surrounded by a fibrous membrane known as the perichondrium. This perichondrium is similar to the periosteum in structure and function. The articular cartilage has no perichondrium and thus its regeneration after injury is inadequate because the perichondrium plays a major role in regeneration of the cartilage. * When a cartilage calcifies the chondrocytes die and the cartilage is replaced by bone