Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Chapter 5 Bone Physiology: Growth & Repair Composition Development Remodeling Fractures Disorders Changes throughout a Lifetime

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Chemical Composition of Bone 35% organic components Composed of cells, fibers, and organic substances Collagen – abundant 65% inorganic mineral salts Primarily calcium phosphate Resists compression

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Bone Development Ossification (osteogenesis) – bone-tissue formation Membrane bones – formed directly from mesenchyme Intramembranous ossification Other bones – develop initially from hyaline cartilage Endochondral ossification

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Intramembranous Ossification Figure 6.8.(1), (2)

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Intramembranous Ossification Figure 6.8(3), (4)

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Endochondral Ossification All bones except some bones of the skull and clavicles Bones are modeled in hyaline cartilage Begins forming late in 2 nd month of human development Continues forming until early adulthood

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Stages in Endochondral Ossification Figure 6.9

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Anatomy of Epiphyseal Growth Areas In epiphyseal plates of growing bones Cartilage is organized for quick, efficient growth Cartilage cells form tall stacks Chondroblasts at the top of stacks divide quickly Pushes the epiphysis away from the diaphysis Lengthens entire long bone

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Anatomy of Epiphyseal Growth Areas Older chondrocytes signal surrounding matrix to calcify Older chondrocytes then die and disintegrate Leaves long trabeculae (spicules) of calcified cartilage on diaphysis side Trabeculae are partly eroded by osteoclasts Osteoblasts then cover trabeculae with bone tissue Trabeculae finally eaten away from their tips by osteoclasts

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Postnatal Growth of Endochondral Bones During childhood and adolescence Bones lengthen entirely by growth of the epiphyseal plates Cartilage is replaced with bone tissue as quickly as it grows Epiphyseal plate maintains constant thickness Whole bone lengthens

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Postnatal Growth of Endochondral Bones As adolescence draws to an end Chondroblasts divide less often Epiphyseal plates become thinner Cartilage stops growing Replaced by bone tissue Long bones stop lengthening when diaphysis and epiphysis fuse

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Postnatal Growth of Endochondral Bones Growing bones widen as they lengthen Osteoblasts – add bone tissue to the external surface of the diaphysis Osteoclasts – remove bone from the internal surface of the diaphysis Appositional growth – growth of a bone by addition of bone tissue to its surface

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Growth of Other Types of Endochondral Bones Short bones – arise from a single ossification center Irregular bones – develop from distinct ossification centers Small long bones Form from a primary ossification center and a single secondary ossification center

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Hormonal Regulation of Bone Growth Growth hormone – produced by the pituitary gland Stimulates epiphyseal plates Thyroid hormone – ensures that the skeleton retains proper proportions Sex hormones Promote bone growth Later induces closure of epiphyseal plates

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Bone Remodeling Bone deposit and removal Occurs at periosteal and endosteal surfaces Bone remodeling Bone deposition – accomplished by osteoblasts Bone reabsorption – accomplished by osteoclasts

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Osteoclast – A Bone-Degrading Cell A giant cell with many nuclei Crawls along bone surfaces Breaks down bone tissue Secretes concentrated hydrochloric acid Lysosomal enzymes are released Figure 6.11

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Repair of Bone Fractures Simple and compound fractures Treatment by reduction Closed reduction Open reduction

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Stages of Healing a Fracture Figure 6.12

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Common Types of Fractures Table 6.1

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Common Types of Fractures Table 6.1

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Common Types of Fractures Table 6.1

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Common Types of Fractures Table 6.1

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Disorders of Bones Osteoporosis – characterized by low bone mass Bone reabsorption outpaces bone deposition Occurs most of in women after menopause

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Disorders of Bones Osteomalacia – occurs in adults – bones are inadequately mineralized Rickets – occurs in children – analogous to osteomalacia Paget's disease – characterized by excessive rate of bone deposition Osteosarcoma – a form of bone cancer

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The Skeleton Throughout Life Cartilage grows quickly in youth Skeleton shows fewer chondrocytes in the elderly Bones are a timetable Mesoderm – gives rise to embryonic mesenchyme cells Mesenchyme – produces membranes and cartilage Membranes and cartilage ossify

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The Skeleton Throughout Life Skeleton grows until the age of 18–21 years In children and adolescents Bone formation exceeds rate of bone reabsorption In young adults Bone formation and bone reabsorption are in balance In old age reabsorption predominates Bone mass declines with age