(20).SKELETON SYSTEM

 The skeleton forms the framework of the body, protects vital organs, and works with the muscular system to produce movement. The human adult skeleton is composed of 206 bones. It is divided for study into the axial skeleton and the appendicular skeleton. The axial skeleton consists of the skull, the spinal column, the ribs, and the sternum. The skull consists of eight cranial bones and the 14 bones of the face.
Skull bones are joined by nonmoveable joints (sutures), except for the joint between the lower jaw (mandible) and the temporal bone of the cranium, the temporomandibular joint (TMJ).
 The 26 vertebrae of the spinal column are divided into five regions: cervical (7); thoracic (12); lumbar (5); the sacrum (5 fused); and the coccyx (4 to 5 fused).
Between the vertebrae are disks of cartilage that add strength and flexibility to the spine.  The appendicular skeleton consists of the bones of the arms and legs, the shoulder girdle, and the pelvis. Each of the two pelvic bones is formed of three fused bones. The large, flared, upper bone is the ilium.

 BONE FORMATIONN:










Bone is formed by the gradual addition of calcium and phosphorus salts to cartilage, a type of dense connective tissue. This process of ossification begins before birth and continues to adulthood. Although bone appears to be inert, it is actually living tissue that is constantly being replaced and remodeled throughout life. Three types of bone cells are involved in these changes: osteoblasts are the cells that produce bone; osteocytes are mature bone cells; and osteoclasts are involved in the breakdown of bone tissue to release needed minerals or to allow for reshaping and repair. The process of destroying bone so that its components can be taken into the circulation is called resorption. This process occurs normally throughout life; in disease states, resorption may occur more rapidly or more slowly than bone production. 

 Joints:  The joints or articulations are classified according to the degree of movement they allow. 

A suture ;

is an immovable joint held together by fibrous connective tissue, as is found between the bones of the skull.
  SYMPHYSIS;   is a slightly movable joint connected by fibrous cartilage. Examples are the joints between the bodies of the vertebrae and the joint between the pubic bones.

  freely movable joint ; is called a synovial joint or diarthrosis. Such joints allow for a wide range of movements.
Tendons attach muscles to bones to produce movement at the joints. Freely moveable joints are subject to wear and tear, and they therefore have some protective features. The cavity of a diarthrotic joint contains synovial fluid, which cushions and lubricates the joint. This fluid is produced by the synovial membrane that lines the joint cavity. The ends of the articulating bones are cushioned and protected by cartilage.
 Synovial joints are stabilized and strengthened by ligaments, which connect the articulating bones. 

A bursa;  is a small sac of synovial fluid that cushions the area around a joint. Bursae are found at stress points between tendons, ligaments, and bones. Structure of a Long Bone ; A typical long bone has a shaft or diaphysis composed of compact bone tissue. 

Within the shaft is a medullary cavity containing the yellow form of bone marrow, which is high in fat. The irregular epiphysis at either end is made of a less dense, spongy bone tissue containing the blood-forming red bone marrow. A thin layer of cartilage covers the epiphysis and protects the bone surface. Between the diaphysis and the epiphysis at each end of the bone, in a region called the metaphysis, is the growth region or epiphyseal plate. When the bone stops growing in length, this area becomes fully calcified but remains visible as the epiphyseal line. The thin layer of fibrous tissue that covers the outside of the bone, the periosteum, nourishes and protects the bone and also generates new bone cells for growth and repair. Long bones are found in the arms, legs, hands, and feet. Other types of bones are described as flat (i.e., cranial bones), short (i.e., wrist and ankle bones), or irregular (i.e., facial bones and vertebrae). thanks to everybody..god bless this website and it's followers.as well as its creator.if you want read this lesson in hausa.visit,my other website, @ 

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