Bone Tissue Chapter 7

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 and physiologically controlled 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 – 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

Structure of Bone Figure 5.1

Histology Four main types of bone cells – Osteogenic (osteoprogenitor) cells give rise to osteoblasts, osteocytes – Osteoblasts Bone-forming cells Found along endosteum and periosteum Secrete osteocalcin – Osteocytes Former osteoblasts that have been trapped in their lacunae Maintain bony matrix Strain sensors – Octeoclasts Bone-dissolving cells Matrix – composed of inorganic and organic components Inorganic component – Hydroxyapaptite Composed mainly of CaPO4 salt 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 spicules and 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

Calcium Homeostasis Hypocalcemia – Leads to excitability of nervous system Hypercalcimia – Leads to depression of nervous system

Calcium Homeostasis Regulated by three hormones – Calcitonin Secreted by parafollicular cells in thyroid Promote deposition of calcium in the bone Decreases calcium level in blood – Inhibit osteoclasts, promote osteoblast activity – Parathyroid hormone Secreted by parathyroid glands Promotes bone resorption Increases calcium level in blood – Raise osteoclast population – Promotes calcium reabsorption in kidneys – Promotes calcitriol synthesis – Inhibits collagen deposition – Calcitriol Increases calcium level in blood – Promotes more calcium absorption by intestine – Promotes reapsorption from skeleton

Fractures and Repair Fracture – Break in the bone – Two types Stress Pathological Table 7-2 for classifications Granulation tisssue – 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