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Bone Tissue- Chapter 5
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Bone Functions
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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.
5-3
Bone Cell Types
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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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80%
20%
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.
– Pott’s- 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= articulation=arthrosis.
• 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 fibrous
capsule 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
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