Skeletal Tissues and Bone Repair

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Skeletal Tissues and Bone Repair

• Chapter 6

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Functions of bones

• Support Bone bears body weight cartilage
  provides firm yet flexible support ligaments
  attach bones to bones
• Protection Bone protects organs
• Movement contraction of muscles moves bones and
  produces movement
• Storage minerals (Ca P) and fat
• Blood cell formation bone marrow gives rise to
  blood cells and platelets

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Quick Review Connective Tissues

• Bone, cartilage, tendons, and ligaments are
  connective tissues.
• The matrix of these tissues contains
• Collagen (a tough protein)
• Ground substance (polysaccharide molecules)
• Water
• Minerals

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Quick Review Connective Tissues

• Tendons and ligaments contain lots of collagen
  making them tough, but flexible
• Cartilage contains collagen and ground substance
  making it rigid, but able to be compressed good
  shock absorber
• Bone contains collagen and minerals (like
  reinforced concrete) leading to a flexible
  strength in bone

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General Features of Bones

• SHAPES
• Long bones longer than they are wide
• Short bones broad as they are long
• Flat bones thin, flattened shape
• Irregular bones shapes dont fit the other
  categories

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General Features of Bones

• TYPES of BONE
• Compact Bone is mostly solid matrix and cells
• Cancellous (spongy) bone consists of a lacy
  network of bone with many small, marrow-filled
  spaces

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Structure of a Typical Long Bone

• AREAS of LONG BONE
• Diaphysis (shaft) collar of compact bone around
  a medullary cavity
• Epiphyses (bone ends) mostly spongy bone with
  compact bone exterior. Cartilage is seen in the
  ends of long bones at the articular surface
  (hyaline cartilage) and epiphyseal plate (growth
  plate)

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Structure of a Typical Long Bone

• CAVITIES of LONG BONE
• Medullary cavity (in diaphysis) filled with
  yellow marrow consists mostly of fat
• Other smaller cavities (in epiphyses) filled
  with red marrow consist of blood-forming cells
  and is the site of blood formation in adults

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Structure of a Typical Long Bone

• MEMBRANES of LONG BONE
• Periosteum- a dense CT on the bones outer
  surface protects and provides an anchoring point
  for tendons and ligaments contains nerves, lymph
  vessels, and blood vessels.
• Endosteum- thinner CT that lines the medullary
  cavity
• Both membranes contain osteoblasts (bone-building
  cells) and osteoclasts (bone-killing cells)

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Bone Tissue Vocabulary

• Osteoblast bone building cells
• Osteocyte osteoblast surrounded by a matrix
  (bone cell)
• Lamellae thin sheets of extracellular matrix
  (has osteocytes between the layers)
• Lacunae hollow spaces which house osteocytes
• Canaliculi tiny canals extending from
  osteocytes into the lamellae

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Compact Bone

• Forms most of the diaphysis of long bones and
  thinner surfaces of other bones
• Is made of osteons (a.k.a Haversian systems)
  seen in cross-section, osteons look like targets
• Lamellae are organized into sets of concentric
  rings each surrounding a central canal (a.k.a.
  Haversian canal)
• Central canals contain blood vessels
• Dense but riddled with tiny canals
• Nutrients leave blood vessels of central canal
  and diffuse to the osteocytes through the
  canaliculi.

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Diagram of a single osteon
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Cancellous bone

• Located mainly in the epiphyses of long bones and
  sandwiched in middle of all other bones
• Consists of delicate rods of bone tissue called
  trabeculae spaces between these rods are filled
  with bone marrow
• No blood vessels penetrate the trabeculae no
  central canals
• Nutrients exit vessels in the marrow and diffuse
  through canaliculi to the osteocytes

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Bone Formation

• Ossification is the formation of bone by
  osteoblasts
• When osteoblasts are surrounded by bone matrix,
  they become osteocytes (mature bone cells)
• All bones begin as hyaline cartilage as a fetus
  develops, bone forms on pre-existing connective
  tissue either CT membranes or cartilage

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Intramembranous Ossification

• Occurs when osteoblasts produce bone in CT
  membranes, primarily in the flat bones of the
  skull osteoblasts line up on CT fibers and
  deposit bone matrix to form trabeculae.
• The initial spongy bone is then remodeled to
  enlarge or form compact bone.

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Endochondral Ossification

• Occurs at the base of the skull and in other
  bones
• Steps
• 1. Cartilage cells (chondrocytes) increase in
  number they create a shape similar to mature
  bone this shape is covered with a CT covering
  (perichondrium) blood vessels
• 2. Osteoblasts form and produce a collar of bone
  around the diaphysis chondrocytes enlarge and
  the cartilage matrix calcifies perichondrium
  becomes the periosteum

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Endochondral Ossification (steps cont)

• 3. Blood vessels and osteoblasts invade the
  calcified cartilage (in diaphysis) forming a
  primary ossification center osteoblasts form
  trabeculae
• 4. A medullary cavity forms in the diaphysis as
  osteoclasts remove bone and calcified cartilage
  which is replaced by bone marrow later a
  secondary ossification center forms in the
  epiphyses.
• At birth, most long bones are ossified except at
  epiphyses Nearly all bones are ossified by age
  25.

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Bone Growth

• Growth in diameter
• Osteoblasts deposit new bone matrix on the
  surface of bones, under the periosteum
• Growth in length (occurs in the epiphyseal plate)
  
• New cartilage is produced on the epiphyseal side
  of the plate as chondrocytes divide and form
  vertical stacks of cells
• Chondrocytes enlarge the matrix calcifies then,
  chondrocytes die, are removed by osteoclasts, and
  are replaced by osteoblasts
• This process produces bone on the diaphyseal side
  of the plate

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Bone Remodeling

• Involves the removal of existing bone by
  osteoclasts and the deposition of new bone by
  osteoblasts
• Remodeling is involved in
• Bone (length) growth at the epiphyseal plate
• Maintaining the thickness of compact bone
  relative to the medullary cavity (to prevent the
  compact bone of the diaphysis from becoming too
  heavy)
• Changes in bone shape
• Adjustment of bone to stress
• Bone repair
• Calcium regulation in body fluids

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Bone and Calcium Homeostasis

• Bone stores Ca maintaining blood Ca levels is
  critical for normal muscle and nervous system
  function
• Ca moves into bone as osteoblasts build new bone
  Ca moves out of bone as osteoclasts break down
  bone
• Decreasing blood Ca levels stimulates parathyroid
  hormone (PTH) from the parathyroid glands
• Increasing blood Ca levels stimulates calcitonin
  from the thyroid gland

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PTH vs. Calcitonin

• PTH
• Stimulates osteoclast activity
• Increases bone breakdown
• Increases blood Ca levels
• Increases Ca reabsorption from urine by kidneys
• Stimulates the kidneys to form vitamin D, which
  increases Ca absorption from the small intestines

• Calcitonin
• Decreases osteoclast activity
• Decreases blood Ca levels

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Steps of Bone Repair

• 1. The bone is broken, and blood vessels are
  damaged bleeding occurs and a clot forms
• 2. Invading cells and blood vessels form CT
  fibers and cartilage that holds the bone
  fragments together called a callus (2 3 days)
• 3. Osteoblasts enter the callus and form spongy
  bone immobilization is critical (4 6 weeks)
• 4. Spongy bone is remodeled to form compact bone
• Healing may require several months however, the
  healed region can be stronger than the adjacent
  bone

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Types of Fractures

• Simple (closed fracture)
• Compound (open fracture)
• Comminuted (broken to small pieces)
• Compression (crushed)
• Depression (broken pieces push inward)
• Impacted (bones are forced together)
• Spiral (bone twists apart)
• Greenstick (incomplete fracture kids)

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Bone diseases

• Rickets - soft bones in children inadequate
  diet or amounts of sunlight needed for vitamin D
  production (necessary for Ca absorption)
• Osteogenesis Imperfecta genetic, brittle bone
  disease due to insufficient collagen in bone
• Osteomalacia - soft bones in adults caused by
  poor deposition of calcium salts insufficient
  calcium or vitamin D in diet
• Osteomyelitis bacterial infection in bone
  (Staph infection)
• Osteoporosis (see next slide)

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Osteoporosis

• Bone re-absorption outpaces bone deposit
• In women usually due to a decrease in estrogen
  (menopause, removal of ovaries, amenorrhea,
  anorexia, cigarette smoking)
• In males usually due to a decrease in
  testosterone (less of problem b/c bone is denser
  and levels dont decrease until after age 65
  very slowly)
• In everyone inadequate diet or absorption of
  Ca inadequate exercise or paralysis leading to
  bone loss

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Bone Markings

• Projections (t names) for attachment of muscle
  and ligaments
• Tuberosity
• Crest and line
• Trochanter
• Tubercle
• Epicondyle
• Spine

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More bone markings

• Projections that help to form joints
• Head
• Facet
• Condyle

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More Bone Markings

• Depressions or holes (f names) for blood
  vessels and nerves
• -Meatus- external auditory meatus
• -Sinus- cavity in bone
• -Groove
• -Fossa
• -Fissure
• -Foramen- foramen magnum