+ The Skeletal System Bone Growth and Repair

Types of Bone Cells Slide 5.15 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Osteocytes  Mature bone cells  Osteoblasts  Bone-forming cells  Osteoclasts  Bone-destroying cells  Break down bone matrix for remodeling and release of calcium

Bone Development Slide 5.12 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  In embryos, the skeleton is primarily hyaline cartilage  Uses hyaline cartilage “bones” for bone construction  During development, much of this cartilage is replaced by bone  Begins in second month of development Bone Development

Bone Growth Slide 5.13a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Epiphyseal plates allow for growth of long bone during childhood  New cartilage is continuously formed  Older cartilage becomes ossified  Cartilage is broken down  Bone replaces cartilage Bone Growth Animation

+ Hormonal Regulation of Bone Growth During Youth During infancy and childhood, epiphyseal plate activity is stimulated by growth hormone During puberty, testosterone and estrogens: Initially promote adolescent growth spurts Cause masculinization and feminization of specific parts of the skeleton Later induce epiphyseal plate closure, ending longitudinal bone growth

+ Bone Remodeling Bones are remodeled continually in response to changes in two factors: Calcium Levels in the blood The pull of gravity and muscles on the skeleton

+ Bone remodeling When blood calcium levels drop below homeostatic levels, the parathyroid glands release Parathyroid hormone PTH activates osteoclasts to break down bone matrix and release calcium ions into the blood Bone remodeling is essential if bones are to retain normal proportions and strength during long-bone growth Accounts for the fact that bones become thicker and form large projections to increase strength in areas where bulky muscles are attached

+ Fractures and Bone Healing

Bone Fractures Slide 5.16 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  A break in a bone  Types of bone fractures  Closed (simple) fracture – break that does not penetrate the skin  Open (compound) fracture – broken bone penetrates through the skin  Displaced – the bone snaps into two or more parts and moves sot that the two ends are NOT lined up straight  Non-displaced – the bone cracks either part of all of the way through, but does move and maintains its proper alignment

+ Transverse fracture Usually caused by directly applied force to fracture site Broken straight across the bone

+ Spiral or Oblique Caused by violence transmitted through limb from a distance (twisting movements)

+ Greenstick Occurs in children: bones soft and bend without fracturing completely

+ Crush fractures Fracture in cancellous bone: result of compression (osteoporosis)

+ Burst fracture Occurs in short bones, e.g. vertebra from strong direct pressure such as impaction of disc.

+ Fracture dislocation/subluxation Fracture involves a joint: results in malalignment of joint surfaces.

+ Impacted fracture Bone fragments are impacted into each other.

+ Comminuated fracture Two or more bone pieces - high energy trauma

+ Comminuated fractures can require serious hardware to repair.

+ Stress fracture Abnormal stress on normal bone (fatigue fracture) or normal stress on abnormal bone (insufficiency fracture).

+ Bone Repair!

+ Repair of Bone Fractures Slide 5.18 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 1.Hematoma (blood-filled swelling) is formed 2.Break is splinted by fibrocartilage to form a callus 3.Fibrocartilage callus is replaced by a bony callus 4.Bony callus is remodeled to form a permanent patch

+ Stages in the Healing of a Bone Fracture Slide 5.19 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5.5

+ Stages in the Healing of a Bone Fracture Hematoma formation Torn blood vessels hemorrhage A mass of clotted blood (hematoma) forms at the fracture site Site becomes swollen, painful, and inflamed Figure Hematoma Hematoma formation

+ Stages in the Healing of a Bone Fracture Fibrocartilaginous callus forms Granulation tissue (soft callus) forms a few days after the fracture Capillaries grow into the tissue and phagocytic cells begin cleaning debris Figure Fibrocartilaginous callus formation External callus New blood vessels Spongy bone trabeculae Internal callus (fibrous tissue and cartilage)

+ Stages in the Healing of a Bone Fracture The fibrocartilaginous callus forms when: Osteoblasts and fibroblasts migrate to the fracture and begin reconstructing the bone Fibroblasts secrete collagen fibers that connect broken bone ends Osteoblasts begin forming spongy bone Osteoblasts furthest from capillaries secrete an externally bulging cartilaginous matrix that later calcifies

+ Stages in the Healing of a Bone Fracture Bony callus formation New bone trabeculae appear in the fibrocartilaginous callus Fibrocartilaginous callus converts into a bony (hard) callus Bone callus begins 3-4 weeks after injury, and continues until firm union is formed 2-3 months later Figure Bony callus formation Bony callus of spongy bone

+ Stages in the Healing of a Bone Fracture Bone remodeling Excess material on the bone shaft exterior and in the medullary canal is removed Compact bone is laid down to reconstruct shaft walls Figure Bone remodeling Healing fracture

+ Repair of Bone Fractures Slide 5.18 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Hematoma (blood-filled swelling) is formed  Break is splinted by fibrocartilage to form a callus  Fibrocartilage callus is replaced by a bony callus  Bony callus is remodeled to form a permanent patch