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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 Bone80% 20%

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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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• 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.

Joints

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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