Musculoskeletal System Flashcards
Functions of the skeletal system
Support Protection Movement Calcium and phosphorous reserve Haemopoiesis Fat storage
Number of bones in the axial skeleton
80
Some paired
Number of bones in the appendicular skeleton
126
All paired
Function of axial skeleton
Support
Protection
Haemopoiesis
Function of appendicular skeleton
Movement
Fat storage
Type of bone marrow in axial and appendicular skeletons
Axial - red bone marrow
Appendicular - yellow bone marrow
Importance of calcium reserve
Calcium imbalance can impact on muscle contraction and calcification of bone - reserve needed to avoid adverse effects
Importance of phosphorous reserve
Phosphorous is a building block of cells, reserve needed for repair and maintenance
Epiphysis
End of long bone
Contains red bone marrow
Metaphysis
Junction of long bone between epiphysis and diaphysis
Diaphysis
Body of long bone
Contains yellow bone marrow
Describe the forces acting on a long bone
At the epiphysis the forces acting on the long bone are perpendicular to the surface for compression
At the diaphysis the forces are parallel to the surface for structure and strength
Describe the organisation of the epiphysis
Articular cartilage on the outside surrounding thin layer of compact bone
Thick layer of spongy bone consisting of trabeculae completely covered in endosteum
Blood vessels inside compact bone and between trabeculae
Gaps formed by trabeculae network are called medullary cavities which are filled with red bone marrow
Describe the organisation of the diaphysis
Periosteum with Sharpeys fibres on the inside surround thick layer of compact bone
Thin layer of endosteum on the inside lining medullary cavity consisting of yellow bone marrow
Bone vessels and nerves are found in the periosteum
Sharpeys fibres
Perforating fibres that are incredibly strong and attach the periosteum to the bone itself
Periosteum
Outer fibrocellular sheath surrounding bone
Endosteum
Thin inner fibrocellular layer lining medullary cavity
Covers all bony surfaces
Articular cartilage
In replacement of periosteum at epiphysis, found mostly at joints
Tendons
Bundles of collagen fibres oriented in same direction to resist tension
Collagen fibre Type I
Thick and strong
Located in areas where there is lots of tension
Describe the extracellular matrix of bone
Organic fibres - 1/3 of dry weight, consist of collagen fibres type I and V, resist tension
Inorganic ground substance - 2/3 dry weight, consist of hydroxyapatite and resists compression
Osteogenic cells
Cell reserve - unspecialised stem cells
Found in periosteum and endosteum and central canals of compact bone
Can divide and supply developing bone with bone forming cells
Osteoblast cells
Bone formation
Usually in a layer under the periosteum or endosteum, wherever new bone is being formed
Synthesis, deposition and calcification of osteoid
Osteocyte cells
Bone maintenance
Trapped within lacunae inside bone
Can communicate with neighbouring cells through long cellular processes inside canniculi
Bone tissue maintenance and localised minor repair
Live lattice tissue inside bone
Rapid calcium exchange
Osteoclast cells
Bone destruction
Sites where bone resorption is occurring
Secretes acid and enzymes to dissolve mineral and organic components of bone
Hydroxyapatite
Ca10(PO4)6OH2
Crystallised and mineralised salt allowing calcium and phosphorous reserve
Osteoid
Organic extracellular matrix of bone synthesised by osteoblasts prior to mineral deposition
70% collagen, 30% proteoglycans, water and other proteins
Calcification makes the bone strong and dense
Calcification
Osteoid, a precursor matrix, is infiltrated with bone salts called hydroxyapatite making the bone strong, dense and impenetrable to nutrient diffusion via water displacement and diminishing fluid levels
Describe the process of osteogenic cell to osteocyte
Mesenchyme Osteogenic cell Osteoblast Osteocyte Fusion of monocyte progenitor cells leads to osteoclast
Canaliculi
Microscopic canals between the lacunae of ossified bone
Lacunae
A small space containing an osteocyte in bone or chondrocyte in cartilage
Processes of bone remodelling
Appositional growth
Bone resorption
Describe why bone can’t remodel by interstitial growth
Interstitial growth is a process that occurs in derfomable soft tissues. Bone is too rigid to grow by cells dividing within the tissue to make more so it can only grow by adding cells onto existing tissue
Briefly describe endochondral ossification
Growth of the epiphysis - because it’s covered in cartilage it can’t grow appositionally, i.e. put bone tissue down on top of the cartilage. Instead, the epiphysis and metaphysis come apart across the epiphyseal line where new bone tissue its put. The epiphysis moves away from the metaphysis which then tries to catch up. When they fuse again, bone growth stops.
Describe the layers of bone from the periosteum to the medullary cavity
Periosteum (fibrocellular layer) - blood vessels and nerves - osteogenic cells Mineralised bone (live lattice of bone) - osteocytes in their lacunae - osteocyte (cellular processes in canaliculi) Endosteum (fibrocellular layer) - osteogenic cells Medullary cavity and bone marrow - blood vessels
‘Resting’ periosteum or endosteum
No osteoblasts present - only dormant osteogenic cells meaning these fibrocellular levels are not currently active or growing
Describe the process of appositional growth
Periosteum becomes active when osteogenic cells which divide and differentiate into osteoblasts
Osteoblasts deposit osteoid which calcifies the bone
Some osteoblasts become trapped in the lacunae, eventually becoming osteocytes
Growth stops, osteoblasts convert back into osteogenic cells or die
Osteoid is fully calcified, periosteum becomes resting
Describe the process of bone resorption
Monocyte precursor cells leave blood vessels and fuse together on the bone surface forming a syncytium called osteoclast
Osteoclasts secrete acid and enzymes to dissolve the bone
Osteoclasts eventually undergo apoptosis, ending resorption
Blood vessels grow into the space created by the bone dissolution
Describe how bone density could be affected by bone growth
Resorption and appositional growth occur throughout the skeleton constantly but independently of each other. Because appositional growth creates new bone tissue and resorption dissolves old bone tissue, if one occurs much more than the other it can cause an increase or decrease in bone density
Describe how estrogen plays a role in bone density
Estrogen has been shown to regulate osteoclast activity. With a decrease in estrogen levels, especially during menopause, osteoclasts become rampant and dissolve bone more than they should, decreasing bone density and increasing chance of osteoporosis
Immature bone
Also known as woven bone
Common in infants, by the time a child has reached age 3 most immature bone has been replaced by mature bone
Collagen is randomly arranged meaning it is fairly pliable and not very strong
Mature bone
Also known as lamellar bone i.e. layered
Collagen fibres are put down in the same direction within a layer but between layers vary the angle to 90 degrees. This allows bone to withstand forces from many different directions making it significantly stronger
Could be spongy or compact
Spongy bone
Type of mature bone
Also known as cancellous or trabecular
Many trabeculae increases the surface area of the bone which increases the blood supply. Good supply means the bone remodels quickly
Maximum width of a trabecula is 0.4mm
Compact bone
Type of mature bone
Also known as cortical bone
Classified by containing osteons
Variable thickness but normally more than 0.4mm
Also contains interstitial and circumferential lamellae and Volkmanns canals which are perpendicular to the bone surface
Blood vessels run through
Osteon
Also called Haversian system
Contain a central/Haversian canal parallel to the surface which has blood vessels and nerves running through
Endosteum lines the insides
Alternating arrangement of collagen fibres between concentric lamellae
Periosteum in compact bone
Contains periosteal blood vessels
Outer fibrous layer and inner osteogenic layer
Primary osteon formation
Primary osteons are formed around an existing blood vessel on the surface of bone, normally in the periosteum
Osteoblasts in active periosteum either side of a blood vessel put down new bone forming ridges
Ridges fuse forming a tunnel around the blood vessel lined with endosteum
Osteoblasts in endosteum build concentric lamellae onto tunnel walls which is slowly filled inward
Bone grows outwards as osteoblasts in periosteum build new circumferential lamellae
Secondary osteon formation
Secondary osteons are created inside existing bone
Osteoclasts form and gather in an area that needs to be remodelled and starts boring its way through existing bone
Tunnel is created, osteoblasts move in and line the tunnel wall forming new active endosteum and deposit osteoid onto tunnel walls
Osteoid layer is calcified forming new lamellae and allowing a blood vessel to grow into the tunnel
Osteoblasts deposit concentric lamellae onto tunnel walls, filling it in. Some are trapped in newly deposited lamellar bone and become osteocytes
Tunnel reduces in size and remaining osteoblasts lining Haversian canal die or become bone lining osteogenic cells and contribute to resting endosteum