Functional Musculoskeletal Anatomy A
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Functional Musculoskeletal
Anatomy A!
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Module 2:!
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Hard Tissues, Distal Upper Limb &
Neurovascular Supply of Upper Limb!
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Semester 1!
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Functional Musculoskeletal Anatomy A
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18. Bone Tissue & Growth of Bones!
18.1 Describe the structure of bone tissue in terms of its organic and inorganic components and
their properties!
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Bone Tissue:!
Dense, supportive connective tissue!
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Contains specialised cells!
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Produces solid matrix of calcium salt deposits (INORGANIC)!
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Around collagen fibres (ORGANIC)!
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Bone (osseous) tissue structure:!
Dense matrix!
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minerals!
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osteocytes (mature bone cells)!
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protein!
Covering - ‘Periosteium’!
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covers outer surface of bone!
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consists of outer fibres & intercellular layers!
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Bone Matrix:!
Minerals!
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2/3 of bone matrix is calcium phosphate - Ca3(PO4)2!
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Reacts with calcium hydroxide to form crystals of hydroxyapatite (dense structure ‣
hardness/toughness of bone)!
Which incorporates other calcium salts & ions!
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Used to repair bones!
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Matrix Proteins!
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1/3 bone matrix = collagen fibres!
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Resilience - stops brittle bones. Reasonably flexible!
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Bone cells!
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2% of bone mass!
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4 types:!
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Osteocytes!
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Mature bone cells that maintain bone matrix!
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Live in lacunae (chamber/pit)!
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Sit between layers (lamellae) in matrix!
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Connect by cytoplasmic extensions through canaliculi in lamellae!
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‘Canaliculi’ = nerve-type structures - connections between different osteocytes to
communicate (usually signals to produce more osteoblasts if bone strengthening is
needed)!
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Do NOT divide!
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Two major functions:!
1. Maintain protein & mineral content of matrix!
2. Help repair damaged bone!
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Functional Musculoskeletal Anatomy A
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18.2 Describe the structure of the two types of bone tissue (spongy & compact) in terms of their
specific function!
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Compact Bone Structure!
- Osteon (Haversian system) is the basic unit (microscopic) - closely packed making it very dense!
- Osteocytes arranged in ‘concentric lamellae’ (rings)!
- Around a central canal containing blood vessels (surounded by endoseium)!
- Perforating (Volkmann’s) canals!
- Perpendicular to central canal!
- Brings blood to centre of osteon (into bone & marrow)!
- Blood supply in remodelling bone is extremely important!
- ‘Circumfrential Lamellae’!
- Lamellae wrapped around the long bone!
- Binds osteons together!
- ‘Interstitial lamellae’ - in between osteons!
- Individual lamellae in osteon arranged in collagen fibres which are perpendicular to each other.
Can resist multiple sheer forces = ‘structurally robust’!
- Matrix is solidly filled with organic ground substance & inorganic salts with lacunae containing
osteocytes)!
- Membrane of compact bone:!
- Periosteum on the outside!
- Covers all bones except parts enclosed in joint capsules!
- Made up of an outer, fibrous layer & an inner, cellular layer!
- “Perforating fibres” = collagen fibres of the periosteum. Connect with collagen
fibres in bone and with fibres of joint capsules; attach tendons & ligaments!
- Functions:!
- Isolates bone from surrounding tissues!
- Provides route for circulatory & nervous supply!
- Participates in bone growth & repair!
- Endosteum on the inside!
- Incomplete cellular layer!
- Lines medullary (marrow) cavity!
- Covers trabecular of spongy bone!
- Lines central canals!
- Contains osteoblasts, osteoprogenitor cells & osteoclasts!
- Active in bone growth & repair!
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Compact Bone Function:!
• Used in weight bearing!
• Protect the organs !
• Support the body !
• Provide levers for the body!
• Store minerals !
• Visible on the outside, dense tissue!
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Functional Musculoskeletal Anatomy A
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18.4 Briefly describe the mechanisms by which long bones grow in length & diameter!
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Bone Development!
- Human bones grow until about age 25!
- Osteogenesis = bone formation!
- Ossification = the process of replacing other tissues with bone!
- Ostoblasts lay down new bone!
- New bone is laid down around the circumference of the shaft in order to increase its diameter!
- The deepest layers of bone are being removed, maintaining a reasonable thickness of cortical
bone & enlarging marrow cavity!
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Calcification:!
- The process of depositing calcium salts!
- Occurs during bone ossification & in other tissues!
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Ossification x2 forms:!
1. Endochondral Ossification !
2. Intramembranous Ossification!
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Endochondral Ossification!
- Ossifies bone that originates as hyaline cartilage (which is most bones) ie. totally dependent on
hyaline cartilage!
- 6 main steps involved:!
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Chondrocytes secrete enzymes (alkaline phosphatase) to begin the process of
mineralization/‘calcification’ (calcium phosphate react with other minerals & crystalline
structure formed inside hyaline cartilage)!
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Bone collar formation. Blood vessels infiltrate & osteoblasts secrete osteoid.!
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Internally, chondrocytes enlarge & secrete vascular endothelial growth factor (VEGF) promotes BV invasion - bringing osteoprogenitor cells, osteoblasts & osteoclasts into
cartilage. Collagen secreted inside!
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Medullary cavity formation - through osteoclasts breaking down bone on inside.
Osteoblasts laying down new bone on outside.!
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Same process occurs in secondary ossification sites: Epiphysis (no medulla though). This
only occurs during birth & puberty - ‘growth spurts’!
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Functional Musculoskeletal Anatomy A
Summary: Bone Development = ossification
o Occurs in 2 distinct phases with about 10 days lag in between 1. Formation of un-mineralised intercellular matrix (osteoid) which occurs as the bone
matrix is secreted by osteocytes 2. Mineralisation of the matrix - uses PG’s, glycoproteins and phosphoproteins which
influence the mineralisation of bones. They form crystals in the matrix (K and Ca
ions) both along & between collagen fibres o Occurs from the hyaline cartilage model (hyaline cartilage = 70% water = good load
bearing tissue)
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Blood Supply of Mature Bones!
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1. Nutrient Artery & Vein!
- Single pair of large blood vessels!
- Enter diaphysis through the nutrient
foramen!
- Femur has more than one pair!
2. Metaphyseal Vessels!
- Supply the epiphyseal cartilage!
- Where bone growth occurs!
3. Periosteal Vessels!
- Blood to superficial osteons!
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- Secondary ossification centres!
Bone Remodelling!
- Adult skeleton maintains itself - involving osteocytes, osteoblasts & osteoclasts!
- Replaces mineral reserves!
- Recycles & renews bone matrix 5-7% per week!
- If deposition is greater than removal, bone gets stronger!
- If removal is faster than replacement, bone gets weaker!
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Effects of Exercise!
- Mineral recycling allows bones to adapt to stress - heavily stressed bones become thicker &
stronger!
- Bone degenerates quickly - up to 1/3 of bone mass can be lost in a few weeks of inactivity!
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Effects of Hormones & Nutrition!
- Dietary source of calcium & phosphate salts (+ small magnesium, fluoride, iron & manganese)!
- Hormone calitriol:!
- made in kidneys!
- helps absorb calcium & phosphorus from digestive tract!
- synthesis requires vitamin D3!
- Growth hormone and thyroxine stimulate bone growth!
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