2. The skeletal system is divided into 2 major parts: Axial skeleton: skull, vertebral column, ribs, sternum Appendicular skeleton: upper and lower limbs Structure and composition of bone: 25% of water 35% of organic solids (ossein, ossseomucoid and osseoalbumin) 45% inorganic salts (calcium, phosphate, magnesium) Histology: Bone is divided into 2 parts Compact bone Spongy bone Compact bone: The external part is called periosteum which consist of outer fibrous layer and inner osteogenic layer called as cambium. The periosteum attaches bone with muscles and tendons. Gives protection, covering, regeneration of bone and healing of fracture.

3. Spongy bone: Found in the inner part of the flat bones, vertebrae, roubded ends of the long bones. It consist of no. of spaces filled with bone marrow The inner lining of marrow cavity is endosteum. The compact bones consist of haversian system which is made up of haversian canal, lamellae and lacunae. The blood vessels, nerves and lymphatics are present in this part.

4. Bone marrow: Found in spongy parts of the bone and bone canal. 2 types: Yellow marrow: contains fat cells for storage of lipids Red marrow: produces RBC Red marrow is jelly like mass present in all the bones during the birth Eventually gets converted to yellow in most of the bones at any age, remains red in ribs, sternum and vertebrae. Functions: Forms Hb and RBC Rich in reticulo -endothelial cells which has role in body defense against the infection or foreign body Helps in formation of thrombocytes from megakaryocytes Forms granulocyte type of WBC Destroys old RBC with the help of reticuloendothelial cells

5. Bone growth Proliferation of osteoblasts to form osteocytes Uptake of calcium by osteoblasts and osteocytes Production of collagen by osteoblasts Calcium and collagen form bone matrix Inhibition of osteoclasts to prevent bone breakdown Increased bone growth leads to more bone cells, bone formation, bone mass and bone strength, and prevents bone fractures and bone disease, such as osteoporosis. Osteoporosis may occur if bone growth is inhibited Bone loss Inhibition of osteoblasts proliferation Reduction of Calcium uptake Reduction of Collagen production Increased bone breakdown by osteoclasts Increased bone loss leads to bone pain, bone fracture, broken bone, bone injury, and other symptoms of osteoporosis. Osteoporosis may occur if more bone loss occurs than bone growth REGULATION OF BONE GROWTH

6. SKELETAL SYSTEM

7. THE AXIAL SKELETONE The skull:

8. The vertebral column:

9. The bones of thorax:

10. THE APPENDICULAR SKELETON The upper limb: The scapula

11. The clavicle

12. The humerus Radius and ulna

13. Bones of wrist and hands:

14. Bones of lower limbs: The pelvis The femur

15. Tibia and fibula