Bone Tissue- Chapter 5

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Bone Tissue- Chapter 5
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Bone Functions

• Support
• Protection
• Assistance in movement
• Mineral storage and release
• Blood cell production
• Triglyceride storage

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Bone Chemistry

• Water (25)
• Organic Constituent (25)
• Collagen.
• A fibrous protein that provide flexibility.
• Inorganic Constituent (50)
• Calcium phosphate and calcium carbonate.
• Mineral salts that provide hardness.

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Bone Cell Types

• Osteogenic cells- stem cells.
• Osteoblasts- bone building cells, secrete matrix
  collagen fibers.
• Osteocytes- mature bone cells that no longer
  secrete matrix.
• Osteoclasts- bone digestion.

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Compact and Spongy Bone
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Compact Bone- the osteon is the basic unit of
structure.
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Histology of Compact Bone

• Concentric Lamellae- calcified matrix surrounding
  a vertically oriented blood vessel.
• Lacuna- a small hollow space, contains
  osteocytes.
• Canaliculus- a small channel filled with
  extracellular fluid that connects lacunae to each
  other, and to the central canal.
• Central Canal- a circular channel that contains
  blood and lymphatic vessels, and nerves.

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Lacunae, Lamellae, Canaliculi, Haversian Canals
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Spongy Bone

• Trabeculae- latticework of thin plates of bone.
• Spaces in between the lattice are filled with red
  marrow, which is where blood cells and platelets
  develop.
• Location- found near ends of long bones and
  inside flat bones. i.e. hipbones, sternum, sides
  of skull, and ribs.

Histology- no true osteons.
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Anatomy of a Long Bone
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Bone Growth in Length

• Epiphyseal plate
• Cartilage cells in this plate divide rapidly.
• Zone of proliferating cartilage.
• Between ages 18-25, the epiphyseal plates close.
• Cartilage cells in the plate stop dividing and
  bone replaces the cartilage.
• Growth in length stops at age 25.

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Bone Growth in Width
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Factors Affecting Bone Growth 1

• Nutrition
• Adequate levels of vitamins and minerals.
• Calcium and phosphorus for bone growth.
• Vitamin C for collagen formation.
• Vitamins K and B12 for protein synthesis.

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Factors Affecting Bone Growth 2

• Hormones
• During childhood growth factors stimulate cell
  division.
• Human growth hormone (hGH)
• Thyroid hormones
• Insulin
• Sex steroids at puberty initiate male and female
  characteristics.

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Hormonal Abnormalities

• Oversecretion of hGH during childhood produces
  giantism.
• Undersecretion of hGH or the thyroid hormones
  during childhood produces dwarfism.
• The epiphyseal plate closes before normal height
  is reached.
• Estrogen is responsible for closing the growth
  plate.
• Both men and women that lack estrogen receptors
  on cells grow taller than normal.

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Bone Remodeling

• Bone Remodeling- the ongoing replacement of old
  bone tissue by new bone tissue.
• Resorption and Deposition
• Osteoclasts- removal of minerals and collagen.
• 4 per year in compact bone.
• 20 per year in spongy bone.
• Osteoblasts- deposition of minerals and collagen.

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Aging and Bone Tissue

• Demineralization- loss of minerals.
• Very rapid in women 40-45 as estrogen levels
  decrease.
• In males, begins after age 60, but is gradual.
• Decrease in protein synthesis
• Decrease in growth hormone.
• Decrease in collagen production, which gives bone
  its tensile strength, this causes bone to become
  brittle and susceptible to fracture.

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• Cold spots indicate
• Decreased metabolism of decalcified bone.
• Fracture.
• Infection.

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Osteoporosis

• Decreased bone mass resulting in porous bones.
• Those at risk
• White, thin, menopausal, smoking, drinking
  females with a family history.
• Athletes who are not menstruating due to reduced
  body fat and decreased estrogen levels.
• People allergic to milk or with eating disorders
  whose intake of calcium is low.
• Prevention or decrease in severity of
  osteoporosis.
• Adequate diet, weight-bearing exercise, and
  estrogen replacement therapy (for menopausal
  women).
• Behavior when young may be most important factor.
  

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Exercise and Bone Tissue

• Mechanical Stress- the pull on bone by skeletal
  muscle and gravity.
• Mechanical stress increases deposition of mineral
  salts and collagen production.

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Lack of Mechanical Stress Results in Bone Loss.
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Fracture- any break in a bone.

• Named for shape or position of fracture
  line.
• Common fracture types
• Open fracture- skin broken.
• Comminuted- broken ends of bones are fragmented.
• Greenstick- partial fracture.
• Impacted- one side of fracture driven into the
  interior of other side.
• Potts- distal fibular fracture.
• Colles- distal radial fracture.
• Stress fracture- microscopic fissures from
  repeated strenuous activities.

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Developmental Anatomy

• Bone- derived from the Mesoderm germ layer.
• 5th Week limb bud appears as mesoderm covered
  with ectoderm.
• 6th Week constriction produces hand or foot
  plate, skeleton now totally cartilaginous.
• 7th Week endochondral ossification begins.
• 8th Week upper lower limbs visible.

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Joints

• Joint- a point of contact between
• Two bones
• Bone and cartilage
• Bone and teeth
• Joint articulationarthrosis.
• Arthrology- the scientific study of joints.
• Synovial Cavity- the space between articulating
  bones.

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Classification of Joints

• Structural classification based upon
• 1) Type of connective tissue holding bones
  together.
• 2) Presence or absence of space between bones.
• Fibrous joint- collagen fibers, no space.
• Cartilaginous joint- cartilage, no space.
• Synovial joint- dense irregular connective
  tissue, space.
• Functional classification based upon movement
• Synarthrosis- immovable.
• Amphiarthrosis- slightly movable.
• Diarthrosis- freely movable.

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Synovial Joints

• Synovial cavity separates articulating bones.
• Freely movable (diarthroses).
• Articular cartilage
• Reduces friction.
• Absorbs shock.
• Articular capsule
• Surrounds joint.
• Thickenings in fibrouscapsule called ligaments.
• Synovial membrane
• Inner lining of capsule.
• Secretes synovial fluid
  containing hyaluronic
  acid (slippery).

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Hinge Joint

• Convex surface of one bone fits into concave
  surface of 2nd bone.
• Monoaxial movement, like a door
  hinge.
• Movements-
• Flexion- decreasing the joint angle.
• Extension- increasing the angle.
• Hyperextension- opening the joint beyond
  the anatomical position.
• Examples
• Knee, elbow, ankle, interphalangeal joints.

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Elbow Joint- hinge type.
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Ball and Socket Joint

• Ball fitting into a cuplike depression.
• Multiaxial movement.
• Movement- occurs around all axes.
• Examples
• Shoulder joint
• Hip joint