Skeletal System: Bones

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Skeletal SystemBones Skeletal Tissues
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Classification of Bones

• Axial Skeleton
• Skull, vertebral column, and rib cage
• Protecting, supporting, or carrying other body
  parts
• Appendicular Skeleton
• Bones of upper and lower limbs and the girdles
  (shoulder hip bones) that attach limbs to axial
  skeleton
• Allow locomotion and manipulation of our
  environment

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Types of Bones

• Long bones
• Short bones
• Flat bones
• Irregular bones

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Long Bones

• Length is longer than the width is wide
• Designed to absorb stress from body weight
• Found in arms, forearms, hands, thighs, legs,
  and feet

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Short Bones

• About equal in length and width, roughly cube
  shaped
• Found in wrist and ankle

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Flat Bones

• Thin, flattened, and usually a bit curved
• Found in cranium, ribs, scapulae, and sternum

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Irregular Bones

• Complicated shapes that do not fit any of the
  previous three categories
• Found in hip bones, vertebrae and bones of the
  face

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Functions of Bones

• Support
• Protection
• Movement
• Mineral Storage
• Blood cell formation

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Bones and Cartilages of the Human Body
Figure 6.1
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Gross Anatomy of Bones Bone Textures

• Compact bone dense outer layer
• Spongy bone honeycomb of trabeculae (thin
  plates of bone interconnected with one another)
  filled with yellow bone marrow (rich in fatty
  tissue for energy storage

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Structure of Long Bone

• Long bones consist of a diaphysis and an
  epiphysis
• Diaphysis
• Tubular shaft that forms the axis of long bones
• Composed of compact bone that surrounds the
  medullary cavity
• Yellow bone marrow (fat) is contained in the
  medullary cavity

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Structure of Long Bone

• Epiphyses
• Expanded ends of long bones
• Exterior is compact bone, and the interior is
  spongy bone
• Joint surface is covered with articular (hyaline)
  cartilage
• Epiphyseal line separates the diaphysis from the
  epiphyses

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Structure of Long Bone
Figure 6.3
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Bone Membranes

• Periosteum double-layered protective membrane
• Outer fibrous layer is dense regular connective
  tissue
• Inner osteogenic layer is composed of osteoblasts
  and osteoclasts
• Richly supplied with nerve fibers, blood, and
  lymphatic vessels
• Endosteum delicate membrane covering internal
  surfaces of bone

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Structure of Short, Irregular, and Flat Bones

• Thin plates of periosteum-covered compact bone on
  the outside with endosteum-covered spongy bone on
  the inside
• Have no diaphysis or epiphyses
• Contain bone marrow between the trabeculae

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Structure of a Flat Bone
Figure 6.4
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Location of Hematopoietic Tissue (Red Marrow)

• In infants
• Found in the medullary cavity and all areas of
  spongy bone
• In adults
• Found in the spongy bone of flat bones, and the
  head of the femur and humerus

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Microscopic Structure of Bone Compact Bone

• Haversian system, or osteon the structural unit
  of compact bone
• Lamella weight-bearing, column-like matrix
  tubes composed mainly of collagen
• Haversian, or central canal central channel
  containing blood vessels and nerves
• Volkmanns canals channels lying at right
  angles to the central canal, connecting blood and
  nerve supply of the periosteum to that of the
  Haversian canal

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Microscopic Structure of Bone Compact Bone

• Osteocytes mature bone cells
• Lacunae small cavities in bone that contain
  osteocytes
• Canaliculi hairlike canals that connect lacunae
  to each other and the central canal

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Microscopic Structure of Bone Compact Bone
Figure 6.6a, b
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Chemical Composition of Bone Organic

• Osteoblasts bone-forming cells
• Osteocytes mature bone cells
• Osteoclasts large cells that resorb or break
  down bone matrix
• Osteoid unmineralized bone matrix composed of
  proteoglycans, glycoproteins, and collagen

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Bone Development

• Osteogenesis and ossification the process of
  bone tissue formation, which leads to
• The formation of the bony skeleton in embryos
• Bone growth until early adulthood
• Bone thickness, remodeling, and repair

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Bone Development

• Intramembranous Ossification
• bones originate within sheetlike layers of
  connective tissues
• broad, flat bones
• skull bones (except mandible)
• intramembranous bones

• Endochondral Ossification
• bones begin as hyaline cartilage
• form models for future bones
• most bones of the skeleton
• endochondral bones

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Formation of the Bony Skeleton

• Begins at week 8 of embryo development
• Hyaline cartilage that makes up fetal bone gets
  covered by osteoblasts
• Eventually most cartilage gets converted to bone,
  except for articular cartilages and the
  epiphyseal plates

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Bone Formation

• Appositional growthincrease in diameter of bone
• Long bone growth depends on a growth hormone
  during puberty
• Growth occurs in the epiphyseal plate (junction
  of diaphysis with each epiphysis) until age
  16-25, with the ossification of the epiphseal
  plate.

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Long Bone Growth and Remodeling
Figure 6.10
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Bone Remodeling

• Retains normal proportions and strength during
  long bone growth
• Two Factors
• Calcium levels in the blood
• Pull of gravity and muscles on the skeleton

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Importance of Ionic Calcium in the Body

• Calcium is necessary for
• Transmission of nerve impulses
• Muscle contraction
• Blood coagulation
• Secretion by glands and nerve cells
• Cell division

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Factors Affecting Bone Development, Growth, and
Repair

• Deficiency of Vitamin A retards bone
  development
• Deficiency of Vitamin C results in fragile
  bones
• Deficiency of Vitamin D rickets, osteomalacia
• Insufficient Growth Hormone dwarfism
• Excessive Growth Hormone gigantism, acromegaly
  
• Insufficient Thyroid Hormone delays bone
  growth
• Sex Hormones promote bone formation stimulate
  ossification of epiphyseal plates
• Physical Stress stimulates bone growth

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Homeostatic Imbalances

• Rickets
• Bones of children are inadequately mineralized
  causing softened, weakened bones
• Bowed legs and deformities of the pelvis, skull,
  and rib cage are common
• Caused by insufficient calcium in the diet, or by
  vitamin D deficiency

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Homeostatic Imbalances

• Osteoporosis
• Group of diseases in which bone reabsorption
  outpaces bone deposit
• Spongy bone of the spine is most vulnerable
• Occurs most often in postmenopausal women
• Bones become so fragile that sneezing or stepping
  off a curb can cause fractures

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Bone Fractures (Breaks)

• Bone fractures are classified by
• The position of the bone ends after fracture
• The completeness of the break
• The orientation of the bone to the long axis
• Whether or not the bone ends penetrate the skin

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Types of Bone Fractures

• Compound (open) bone ends penetrate the skin
• Simple (closed) bone ends do not penetrate the
  skin
• Comminuted bone fragments into three or more
  pieces common in the elderly
• Spiral ragged break when bone is excessively
  twisted common sports injury

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Common Types of Fractures
Table 6.2.1
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Common Types of Fractures
Table 6.2.2
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Common Types of Fractures

• Depressed broken bone portion pressed inward
  typical skull fracture
• Compression bone is crushed common in porous
  bones
• Greenstick incomplete fracture where one side
  of the bone breaks and the other side bends
  common in children

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Common Types of Fractures
Table 6.2.3
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Treatment by Reduction

• Closed reductionbone ends are realigned and put
  back in place by physician.
• Open reductionbone ends are put together with
  pins or wires through surgery
• After reduction, a cast follows to begin healing
  process (simple fracture 6-8 weeks)

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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

Hematoma
Hematoma formation
1
Figure 6.14.1
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Stages in the Healing of a Bone Fracture

• Fibrocartilage callus forms
• Granulation tissue (soft callus) forms a few days
  after the fracture
• Capillaries grow into the tissue and phagocytic
  cells begin cleaning debris

External callus
New blood vessels
Internal callus (fibrous tissue and cartilage)
Spongy bone trabeculae
Fibrocartilaginous callus formation
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Figure 6.14.2
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Stages in the Healing of a Bone Fracture

• Bony callus formation
• Fibrocartilage 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

Bony callus of spongy bone
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Bony callus formation
Figure 6.14.3
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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

Healing fracture
Bone remodeling
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Figure 6.14.4