Bones

Human skeleton Axial skeleton -80 bones (hyoid bone, skull bones, vertebral column and thorax) Appendicular skeleton -126 bones (upper and lower exptremities, pectoral gridle and pelvic girdle) Total – 206 bones Skeleton – 14% of weight of total body

Types of bones Long bone Short bone Flat bone Irregular bone Each bone composed of cancellous (spongy) and cortical (compact) bone

Cancellous bone – found in the ends of long bone and inner layer of the flat bones Cortical bone – found in shaft of long bone and outer layer of flat bones

Long bones Diaphysis Made of thick cortical bone and contains the medullary cavity where bone marrow is stored Diaphyseal cavity is composed primarily of fatty tissue and contains yellow marrow Endosteum is a layer of connective tissue that lines both yellow and red marrow cavity Metaphysis – composed of cancelloes bone

Epiphysis – composed of spongy tissue and contains red marrow which is responsible for hematopoisesis Epiphysial plate (cartilaginous plate) separates the metaphysis form the epiphysis in children which merge after puberty.

Structure of bone Bone is made up of cells, fibers and ground substance with crystallized minerals Bone is DYNAMIC substance (continuously synthesizing and resorbing bone tissues ) Bone cells osteoblast, osteocytes and osteoclasts

Pagets disease- osteitis deformans Pagets disease is characterized by an excess of bone destruction and unorganized bone formation and repair. Second most common metabolic bone disorder

Etiology Cause is unknown Genictc predispositon – 10% of patients viral infection – triggers the disease Autoimmune dysfunction Varcular disorders Vitamin D deficiency in childhood Mechanical stressors to bone

Common sites Usually affects axial skeleton particularly the vertebrae and skull, although the pelvis, femur and tibia are other common sites of disease

Pathophysiology Increase in osteoclast mediated resorption of cancellous bone along with an increase in osteoblast mediated bone formation The new bone is structurally weak and enlarged Bone resorption and bone formation increases resulting in mosaic like mix of abnormal woven and lamellar bone. Mineralization