Copyright © 2010 Pearson Education, Inc. Appositional Growth and Bone Remodeling Normal Calcium Deposition and Removal Conditions That Stimulate Bone Remodeling Types of Bone Fractures Stages of Bone Healing Hormone Imbalances and Bone Density Problems Developmental Aspects of the Skeleton Axial Skeleton: The Skull Axial Skeleton: Vertebrae Bone Growth, Repair, and Axial Skeleton

Copyright © 2010 Pearson Education, Inc. Postnatal Bone Growth Interstitial growth:  length of long bones Appositional growth:  thickness and remodeling of all bones by osteoblasts and osteoclasts on bone surfaces

Figure 6.11 Bone growth (Interstitial growth) Bone remodeling (Appositional Growth) Articular cartilage Epiphyseal plate Cartilage grows here. Cartilage is replaced by bone here. Cartilage grows here. Bone is resorbed here. Bone is resorbed here. Bone is added by appositional growth here. Cartilage is replaced by bone here.

Copyright © 2010 Pearson Education, Inc. Bone Growth, Repair, and Axial Skeleton Appositional Growth and Bone Remodeling Normal Calcium Deposition and Removal Conditions That Stimulate Bone Remodeling Types of Bone Fractures Stages of Bone Healing Hormone Imbalances and Bone Density Problems Developmental Aspects of the Skeleton

Copyright © 2010 Pearson Education, Inc. Bone Deposition Occurs where bone is injured or added strength is needed Requires a diet rich in protein; vitamins C, D, and A; Ca; P; Mg; and Mn Sites of new matrix deposit are revealed by the Osteoid seam Unmineralized band of matrix Calcification front The abrupt transition zone between the osteoid seam and the older mineralized bone Osteoclasts secrete Lysosomal enzymes to digest organic matrix Acids convert calcium salts into soluble forms Dissolved matrix is transcytosed across osteoclast, enters interstitial fluid and then blood Bone Resorption

Copyright © 2010 Pearson Education, Inc. Control of Remodeling What controls continual remodeling of bone? 1.Hormonal mechanisms that maintain calcium homeostasis in the blood 2.Mechanical and gravitational forces Ca is necessary for transmission of nerve impulses, muscle contraction, blood coagulation, secretion by glands and nerve cells, & cell division

Copyright © 2010 Pearson Education, Inc. Hormonal Regulation of Blood Calcium (Ca +2 or Ca 2+ ) * Leptin (produced by adipocytes) has also been shown to influence bone density by inhibiting osteoblasts

Copyright © 2010 Pearson Education, Inc. Mechanical and Gravitational Forces Wolff’s law: A bone grows or remodels in response to forces or demands placed upon it Observations supporting Wolff’s law: Handedness (right or left handed) results in bone of one upper limb being thicker and stronger Curved bones are thickest where they are most likely to buckle Trabeculae form along lines of stress Large, bony projections occur where heavy, active muscles attach Astronauts who spend months in the absence of gravity have weaker and thinner bones Figure 6.13 Load here (body weight) Head of femur Compression here Point of no stress (axis or fulcrum) Tension here

Copyright © 2010 Pearson Education, Inc. Bone Growth, Repair, and Axial Skeleton Appositional Growth and Bone Remodeling Normal Calcium Deposition and Removal Conditions That Stimulate Bone Remodeling Types of Bone Fractures Stages of Bone Healing Hormone Imbalances and Bone Density Problems Developmental Aspects of the Skeleton Axial Skeleton: The Skull Axial Skeleton: Vertebrae

Copyright © 2010 Pearson Education, Inc. Classification of Bone Fractures Based on Four Aspects 3.Orientation of the break to the long axis of the bone: Linear—parallel to long axis of the bone Transverse—perpendicular to long axis of the bone 4.Whether or not the bone ends penetrate the skin: Compound (open)—bone ends penetrate the skin Simple (closed)—bone ends do not penetrate the skin 2.Completeness of the break Complete—broken all the way through Incomplete—not broken all the way through 1.Position of bone ends after fracture: Nondisplaced—ends retain normal position Displaced—ends out of normal alignment Location is also included when describing a particular fracture

Some Types of Fractures (Splintered or crushed in multiple places)

Bone Growth, Repair, and Axial Skeleton Appositional Growth and Bone Remodeling Normal Calcium Deposition and Removal Conditions That Stimulate Bone Remodeling Types of Bone Fractures Stages of Bone Healing Hormone Imbalances and Bone Density Problems Developmental Aspects of the Skeleton Axial Skeleton: The Skull Axial Skeleton: Vertebrae

Hematoma A hematoma forms. Torn blood vessels hemorrhage Clot (hematoma) forms Site becomes swollen, painful, and inflamed 1 Stages in the Healing of a Bone Fracture

Figure 6.15 Hematoma External callus New blood vessels Spongy bone trabecula Internal callus (fibrous tissue and cartilage) A hematoma forms. Torn blood vessels hemorrhage Clot (hematoma) forms Site becomes swollen, painful, and inflamed Fibrocartilaginous callus forms. - Phagocytic cells clear debris - Osteoblasts begin forming spongy bone within 1 week - Fibroblasts secrete collagen fibers to connect bone ends - Mass of repair tissue now called fibrocartilaginous callus 12 Stages in the Healing of a Bone Fracture

Figure 6.15 Hematoma External callus Bony callus of spongy bone New blood vessels Spongy bone trabecula Internal callus (fibrous tissue and cartilage) A hematoma forms. Torn blood vessels hemorrhage Clot (hematoma) forms Site becomes swollen, painful, and inflamed Fibrocartilaginous callus forms. - Phagocytic cells clear debris - Osteoblasts begin forming spongy bone within 1 week - Fibroblasts secrete collagen fibers to connect bone ends - Mass of repair tissue now called fibrocartilaginous callus Bony callus forms. New trabeculae form a bony (hard) callus Bony callus formation continues until firm union is formed in ~2 months 12 3 Stages in the Healing of a Bone Fracture

Figure 6.15 Hematoma External callus Bony callus of spongy bone Healed fracture New blood vessels Spongy bone trabecula Internal callus (fibrous tissue and cartilage) A hematoma forms. Torn blood vessels hemorrhage Clot (hematoma) forms Site becomes swollen, painful, and inflamed Fibrocartilaginous callus forms. - Phagocytic cells clear debris - Osteoblasts begin forming spongy bone within 1 week - Fibroblasts secrete collagen fibers to connect bone ends - Mass of repair tissue now called fibrocartilaginous callus Bony callus forms. New trabeculae form a bony (hard) callus Bony callus formation continues until firm union is formed in ~2 months Bone remodeling occurs. In response to mechanical stressors over several months Final structure resembles original Stages in the Healing of a Bone Fracture

Figure 6.15 Hematoma External callus Bony callus of spongy bone Healed fracture New blood vessels Spongy bone trabecula Internal callus (fibrous tissue and cartilage) A hematoma forms. Torn blood vessels hemorrhage Clot (hematoma) forms Site becomes swollen, painful, and inflamed Fibrocartilaginous callus forms. - Phagocytic cells clear debris - Osteoblasts begin forming spongy bone within 1 week - Fibroblasts secrete collagen fibers to connect bone ends - Mass of repair tissue now called fibrocartilaginous callus Bony callus forms. New trabeculae form a bony (hard) callus Bony callus formation continues until firm union is formed in ~2 months Bone remodeling occurs. In response to mechanical stressors over several months Final structure resembles original Stages in the Healing of a Bone Fracture

Bone Growth, Repair, and Axial Skeleton Appositional Growth and Bone Remodeling Normal Calcium Deposition and Removal Conditions That Stimulate Bone Remodeling Types of Bone Fractures Stages of Bone Healing Hormone Imbalances and Bone Density Problems Developmental Aspects of the Skeleton Axial Skeleton: The Skull Axial Skeleton: Vertebrae

Copyright © 2010 Pearson Education, Inc. Homeostatic Imbalances: Osteomalacia & Rickets Osteomalacia: Calcium salts not deposited Rickets (childhood osteomalacic disease) causes bowed legs and other bone deformities Cause: vitamin D deficiency (lack of sunlight) or insufficient dietary calcium Vitamin D deficiency can further cause depression

Copyright © 2010 Pearson Education, Inc. Homeostatic Imbalances: Osteoporosis Loss of bone mass where bone resorption outpaces deposit Spongy bone of spine and neck of femur become most susceptible to fracture Risk factors Lack of estrogen (post-menopause), calcium or vitamin D; petite body form; immobility; low levels of TSH; diabetes mellitus Treatment Calcium, vitamin D, and fluoride supplements  Weight-bearing exercise throughout life Hormone (estrogen) replacement therapy (HRT) slows bone loss Some drugs (Fosamax, SERMs, statins) increase bone mineral density

Copyright © 2010 Pearson Education, Inc. Paget’s Disease ( Osteitis deformans) Excessive and haphazard bone formation and breakdown, usually in spine, pelvis, femur, or skull Pagetic bone has very high ratio of spongy to compact bone and reduced mineralization Unknown cause (possibly viral) Treatment includes taking calcitonin and biphosphonates

Copyright © 2010 Pearson Education, Inc. Bone Growth, Repair, and Axial Skeleton Appositional Growth and Bone Remodeling Normal Calcium Deposition and Removal Conditions That Stimulate Bone Remodeling Types of Bone Fractures Stages of Bone Healing Hormone Imbalances and Bone Density Problems Developmental Aspects of the Skeleton Axial Skeleton: The Skull Axial Skeleton: Vertebrae

Copyright © 2010 Pearson Education, Inc. Developmental Aspects of Bones: Embryo and Birth Embryonic skeleton ossifies predictably so fetal age easily determined from X rays or sonograms At birth, most long bones are well ossified (except epiphyses) Fontanelles are places where skull bones are joined by fibrous membranes Completely replaced with bone within two years after birth

Copyright © 2010 Pearson Education, Inc. Developmental Aspects of Bones: Later Events Nearly all bones completely ossified by age 25 (ossification of epiphyseal plates, no more bone growth) Bone mass decreases with age beginning in 4th decade (estrogen deficiency in women at menopause may lead to osteoporosis) Rate of loss determined by genetics and environmental factors In old age, bone resorption predominates. Vertebral collapse may occur, resulting in kyphosis. Kyphosis

Copyright © 2010 Pearson Education, Inc. Bone Growth, Repair, and Axial Skeleton Appositional Growth and Bone Remodeling Normal Calcium Deposition and Removal Conditions That Stimulate Bone Remodeling Types of Bone Fractures Stages of Bone Healing Hormone Imbalances and Bone Density Problems Developmental Aspects of the Skeleton Axial Skeleton: The Skull Axial Skeleton: Vertebrae