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Developmental Aspects: Fetal Skull • Infant skull has more bones than the adult skull • Skull bones such as the mandible and frontal bones are unfused • At birth, skull bones are connected by fontanelles • Fontanelles • Unossified remnants of fibrous membranes between fetal skull bones • Four fontanelles • Anterior, posterior, mastoid, and sphenoid Frontal bone Ossification center Posterior fontanelle (a) Superior view Parietal bone Ossification center Posterior fontanelle Mastoid fontanelle (b) Lateral view Frontal suture Anterior fontanelle Parietal bone Occipital bone Frontal bone Sphenoidal fontanelle Temporal bone (squamous portion) Occipital bone Figure 7.35 Developmental Aspects: Growth Rates • At birth, the cranium is huge relative to the face • At 9 months of age, cranium is ½ adult size • Mandible and maxilla are foreshortened but lengthen with age • The arms and legs grow at a faster rate than the head and trunk, leading to adult proportions Developmental Aspects: Spinal Curvature • Thoracic and sacral curvatures are obvious at birth • These primary curvatures give the spine a C shape • Convex posteriorly Figure 7.37 Developmental Aspects: Spinal Curvature •Secondary curvatures •Cervical and lumbar—convex anteriorly •Appear as child develops (e.g., lifts head, learns to walk) Developmental Aspects: Old Age • Intervertebral discs become thin, less hydrated, and less elastic • Risk of disc herniation increases • Loss of stature by several centimeters is common by age 55 • Costal cartilages ossify, causing the thorax to become rigid • All bones lose mass Ankylosing spondylitis •The cause of ankylosing spondylitis is unknown, but genes seem to play a role. •The disease most often begins between ages 20 and 40, but it may begin before age 10. It affects more males than females. Medial tibial stress syndrome (MTSS), tibial periostitis or shin splints • pain associated with MTSS is caused from a disruption of Sharpey's fibers that connect the medial soleus fascia through the periosteum of the tibia where it inserts into the bone Stress Fractures •Stress fractures are tiny cracks in a bone. Stress fractures are caused by the repetitive application of force, often by overuse — such as repeatedly jumping up and down or running long distances. *Disorders associated with Homeostatic Imbalances • Osteomalacia and rickets • Calcium salts not deposited • Rickets (childhood disease) causes bowed legs and other bone deformities • Cause: vitamin D deficiency or insufficient dietary calcium Rickets *Disorders associated with Homeostatic Imbalances • Osteoporosis • Loss of bone mass—bone resorption outpaces deposit • Spongy bone of spine and neck of femur become most susceptible to fracture • Risk factors • Lack of estrogen, calcium or vitamin D; petite body form; immobility; low levels of TSH; diabetes mellitus Figure 6.16 *Osteoporosis: Treatment and Prevention • 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 *Paget’s Disease • 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 calcitonin and biphosphonates Rheumatoid Arthritis (RA) • Chronic, inflammatory, autoimmune disease of unknown cause • Usually arises between age 40 and 50, but may occur at any age; affects 3 times as many women as men • Signs and symptoms include joint pain and swelling (usually bilateral), anemia, osteoporosis, muscle weakness, and cardiovascular problems; RA begins with synovitis of the affected joint • Inflammatory blood cells migrate to the joint, release inflammatory chemicals • Inflamed synovial membrane thickens into a pannus • Pannus erodes cartilage, scar tissue forms, articulating bone ends connect (ankylosis) • Conservative therapy: aspirin, long-term use of antibiotics, and physical therapy • Progressive treatment: anti-inflammatory drugs or immunosuppressants Osteoarthritis (OA) • • • • • • • • • Common, irreversible, degenerative (“wear-and-tear”) arthritis 85% of all Americans develop OA, more women than men Probably related to the normal aging process More cartilage is destroyed than replaced in badly aligned or overworked joints Exposed bone ends thicken, enlarge, form bone spurs, and restrict movement Treatment: moderate activity, mild pain relievers, capsaicin creams, glucosamine and chondroitin sulfate Common, irreversible, degenerative (“wear-and-tear”) arthritis 85% of all Americans develop OA, more women than men Probably related to the normal aging process Developmental Aspects of Bones • Embryonic skeleton ossifies predictably so fetal age easily determined from X rays or sonograms • At birth, most long bones are well ossified (except epiphyses) Parietal bone Occipital bone Mandible Frontal bone of skull Clavicle Scapula Radius Ulna Ribs Humerus Vertebra Ilium Tibia Femur Figure 6.17