Chapter 6 Bones and Skeletal Tissue Objectives • Know the functions of the skeletal system • Understand how bones are classified • Identify the macroscopic and microscopic features of bone • Understand how bone is developed • Know what a fracture is and how it is repaired • Know some bone disorders Skeletal System • Composed of bones, cartilages, and ligaments joined tightly together to form a strong, flexible framework for the body • Skeleton functions – – – – – – Support Protection Movement Electrolyte balance Acid-base balance Blood formation • Osseous tissue http://www.amersol.edu.pe/class09/_09pdelaf/7th/science/webpages/skeleton.html – Connective tissue with a hardened matrix • Deposition of calcium phosphate and other minerals – Part of the composition of a bone Classification of Bones • Classified based on shape and corresponding function • Four categories – Long bones – Short bones – Irregular bones – Flat bones massasoit-bio.net General Features of Bones • Epiphysis – Ends of the bone – Composed of cancellous (spongy) bone • Diaphysis – Shaft of the bone – Composed of compact bone • Medullary cavity – Contains yellow bone marrow – Epiphyiseal plate http://pathologyoutlines.com/bone.html Structure of Bone Figure 5.1 Histology • Four main types of bone cells – Osteogenic (osteoprogenitor) cells • give rise to osteoblasts , osteocytes • Matrix – composed of inorganic and organic components – Osteoblasts • Bone-forming cells • Found along endosteum and periosteum • Secrete osteocalcin • Inorganic component – Hydroxyapaptite • Composed mainly of CaPO4 salt – Osteocytes • Former osteoblasts that have been trapped in their lacunae • Maintain bony matrix • Strain sensors – Octeoclasts • Bone-dissolving cells • Organic components – Protein and carbohydrate • Collagen • Bone is a composite Compact Bone • Osteon (haversian system) – Basic structural unit of compact bone • Central (haversian) canal surrounded by concentric lamellae (matrix) • Perforating canals – Transverse or diagonal passages into the central canal – Originate at nutrient foramen ask.com Spongy Bone • Composed by a network of trabeculae • Spaces filled with red marrow • Beams arranged to sustain stress commons.wikimedia.org Bone Development • Ossification or osteogenesis – Formation of bone • Two methods – Intramembranous ossification – Endochondral ossification Intramembranous Ossification • Produces flat bones of skull and clavicles • Starts with osteoid • End with diploe massasoit-bio.net Endochondral Ossification • Bone develops from a hyaline model trjohn.blogspot.com Bone Growth and Remodeling • Bone Elongation – Involves epiphyseal plates • Hyaline cartilage between to transitional zones (metaphysis) • Zones of mataphysis – – – – – Reserve cartilage Cell proliferation Cell hypertrophy Calcification Bone deposition • Spongy bone nzdl.org Bone Growth and Remodeling • Interstitial growth – Result from growth of cartilage within the metaphysis – Finite process • Epiphyseal line • Appositional growth – Growth in diameter and thickness • Circumferential lamellae • Remodeling – Wolff’s law of bone • The architecture of bone is determined by the mechanical stresses placed up it. – Bone adapts to withstand stress Physiology of Osseous Tissue • Mineral deposition – Calcium and phosphate are allowed to reach their solubility product • Precipitate in the matrix – Ectopic ossification • Abnormal calcification of soft tissue – Calculus • Mineral resorption – HCl secreted by osteoclasts – Acid phosphatase • Absorbs collagen Fractures and Repair • Fracture – Break in the bone – Two types • Stress • Pathological • See table 6-2 • Granulation tissue – Fibrous mass of capillaries and cells within hematoma medical-definitions.com Bone Disorders • Osteoporosis – Sever loss of bone density • Osteoclast more active than osteoblasts • Osteosarcoma – Most common and deadly form of bone cancer • Metastasizes quickly • Osteogenesis imperfecta – Brittle bones • Defect in collagen deposition