Muscoskeletal Flashcards
What are the two main skeletal regions, # of bones and the main regional differences in function
Axial skeleton (core) : 80 bones (some paired)
Appendicular skeleton (outside) : 126 bones ( all paired)
-Regional differences is that axial is mainly for support/protection and has Haemopoeisis and -Appendicular is for movement and fat storage
What are the 6 functions of the skeletal system
Support (hand soft tissue),
Protection (hard and dense),
Movement (framework for pulling),
Ca+ (for AP& muscle contraction) and Phosphorous (building body) reserves,
Haemopoeisis (red bone marrow)
Fat storage (yellow bone marrow)
What is the regional zones of long bone
At the ends are the epiphyses, Then inwards of that there is are transitory region called metaphyses, and then middle is the Diaphysis.
Describe the layers of Epiphysis from out to in
Epiphysis has 3 layers
Outermost is Articular cartilage: in contact with another bone
Thin layer of Compact bone
5 Blood vessels: (inside compact bone and between trabeculae-> into the medullary cavities)
Spongy bone- made of trabeculae covered in Endosteum with Medullary cavities in between containing red bone marrow.
Describe the layers of Diaphysis from out to in
Outermost is the Periosteum (outer fibrocellular sheath surrounding bone).
5-3 Blood vessels and nerves in the periosteum to compact bone
Perforating Sharpey’s fibers: (provide strong anchorage of collagen fibres to transition Periosteum to compact bone- tendons attach here)
Thick layer of Compact bone
Endosteum : fibrocellular layer lining the medullary cavity
Medullary cavity: yellow bone marrow
What are the main differences between the Epiphysis and the Diaphysis
The epiphysis receives uniform perpendicular forces like a roof, so therefore has trabeculae cross structures
The Diaphysis receives parallel compression forces therefore has a thick compact bone section like walls
What is a connective tissue
It is Cells + ECM. ECM is made of fibres and grounds substance
Compare the properties that make bone a specialised connective tissue : Fibres vs Ground substance (forces, organicness, dry weight) and Cells
Fibres: Type 1 Collagen=1/3 dry weight. Resists stretching/pulling force ( tension)
GS: Hydroxyapatite (Ca and P store) =2/3 dry weight. Resists crushing, squeezing force (compression)
Overall Bone resists Torsion (twisting force)
Cells: Osteo genic, blast, cyte, clast
Describe the Precursor, location, function of Osteogenic cell/ Osteoprogenitor cell
Precursor: Unspecialised stem cell from Mesenchyme, the embryonic CT
Location: Surface of bone in the periosteum and endosteum. Also found in the central canals of compact bone
Function: Normally dormant/resting but can divide and supply developing bone with bone forming cells
Describe the Precursor, location, function of Osteoblast cell
Precursor: Osteogenic cell
Location: Usually in the layer under the peri or endosteum of active bone-> wherever new bone is being formed
Function: Synthesis and depositation and calcification of the osteoid
What is the osteoid
The organic ECM matrix (mostly collagen) of bone, synthesised by osteoblasts prior to mineral depositation.
Made of 70% collagen, 30% proteoglycans other proteins and water.
What is calcification and its rate + limitations of rate
Calcification is the deposition of mineral salts, primarily hydroxyapatite in a framework of collagen fibres, making the tissue harden.
The rate is initially very fast but then gets very slow (years) because the calcification means that nutrient movement is slow because of dense + displacement of water.
Describe the Precursor, location, function of Osteocyte cell
Precursor: Osteoblast
Location: Trapped within lacunae inside bone. Osteocytes can communicate with neighbouring cells through their long cellular processes inside caniculi
Function: Bone tissue maintenance through
live lattice inside bone
localised minor repair
Rapid Ca+ exchange
What is the organic vs inorganic part of bone as a CT
Organic : Type 1 collagen (70%) 30% other proteoglycans + other proteins and water (fibres)
Inorganic is the hydroxyapatite =ground substance
What is the precursor, location and function of Osteoclast
Osteoclasts are from a separate lineage: they come from the fusion of monocyte progenitor cells.
Location: At sites where bone reabsorption is occuring
Function: Secretes acid to dissolve the mineral and enzymes to dissolve the organic components of bone
How does the osteoclast control the destructive enzymes
It has a clear zone close to its ruffled border which collects the enzymes that it secretes and forces it to be endocytosed so it can be neutralised. The enzymes are also only active in an acid environment.
In what layers are the osteogenic cells in inactive bone and what does inactive bone not have ?
Layer under blood vessels in the periosteum, on top of the osteocytes
Under the mineralised bone, in the endosteum, on top of the medullary cavity where there is bone, marrow and bv.
Bones don’t have osteoblasts if inactive
What does bone remodelling mean
Ongoing replacement of old bone tissue, involving bone reabsorption (removal of minerals and collagen fibres) by osteoclasts and appositional growth (addition of minerals and collagen fibres) by osteoblasts on existing bone.
Describe the process of appositional growth 3 steps from active to inactive.
Osteogenic cells divide, forming osteoblasts which deposit osteoid
Some osteoblasts become trapped in the lacunae where they will eventually become osteocytes
When growth stops, osteoblasts can convert back to osteogenic cells or die. The osteoid is fully calcified
Why does the bone grown appositional instead of interstitial
The tissue bone is too rigid for interstitial growth which involves the cells dividing inside the tissue, excreting more ECM and growing the tissue from within. It can only grow by having more stuff added on top.
Are the appositional growth and bone reabsorption always happening at the same time. Where can they occur
No, they occur throughout the skeleton independently of each other. They can occur in the endosteum or the periosteum
How do long bones grow in length and why does it do that
Endochondral ossification= There is a plate of hyaline cartilage that can grow by interstitial growth underneath the epiphysis which is the epiphyseal plate. This cartilage grows, dies then is replaced by bone.
It does it this way because it can’t lay bone down on the articulate cartilage on the ends.
What is the two types of mature lamellar bone and what characterises this bone subset
Mature lamellar bone is characterised by many layers of bone, with collagen fibres put down in the same direction within one layer but alternating out of phase between layers. This enables bone to withstand forces from different directions.
The two types are spongey and compact bone
Describe the structure of spongey/cancellous/trabecular bone and where you find it usually
Made of lamellae arranged in irregular thin columns called trabeculae. The spaces in between are filled with bone marrow (called medullary cavity). Usually found in the interior of a bone, always covered by compact bone for protection.
What are the main different characteristics of spongey bone that is different to compact bone
spongey bone is light which allows the skeleton to move more readily
spongey bone supports red bone marrow so is the site of haemotpoeisis
Spongey bone is the site where bone remodelling is greater because the greater SA means that its easier for osteoclasts to settle on trabeculae to + and - Ca and P
Describe the structure and organisation of compact/cortical bone and where you find it usually
Made of repeating osteons/haversian systems. This consists of concentric lamellae arranged around a central canal containing blood vessels and nerves. There are alternating arrangements of collagen fibres between lamellae.
Compare how spongey bone and compact bone resist stresses- and therefore perform function
Spongey bone isn’t for heavy stresses but its trabeculae are orientated to resist stress from multiple directions and help to support outer cortex of compact bone.
Whereas Compact bone is for heavier stresses, resisting bending because osteons are aligned in the same direction and parallel to the length of the diaphysis. It also thickens in area exposed to large forces.
Whats the difference between circumferential lamellae and interstitial lamellae in compact bone
Interstitial lamellae is areas between neighbouring osteons that contain lamellae with osteocytes and canaliculi. They are fragements of older osteons destroyed during rebuilding.
Whereas Circumferential lamellae is developed during initial bone formation and line the inner and outer boundaries of the compact bone.
What lines the central canal
endosteum
Describe 4 steps how a primary osteon forms from appositional growth
Osteoblasts in the active periosteum either side of the blood vessel put own new bone forming ridges
Bone continues ridges come together and fuse forming a tunnel around the blood vessel. The tunnel is now lined with endosteum.
The osteoblasts in the endosteum build concentric lamellae onto the walls of the tunnel. The tunnel fills inward toward centre
The bone continues to grow outwards as the osteoblasts in the periosteum build new circumferential lamellae.
Process repeats as new ridges fold over blood vessels
Where and what purpose of primary osteon formation happen compared to secondary osteon formation
Primary osteon tunnel formation happens around existing blood vessels in the active periosteum, which happens when bone is growing. Whereas secondary osteons the tunnels are created inside existing bone to help repair/ increase vasculature.
What are the 5 steps of forming a secondary osteon
Osteoclasts form and gather in an area that needs to be remodelled. They start boring its way through the existing bone.
Osteoblasts move in behind the cutting cone and line tunnel wall as new endosteum and start depositing osteoid.
Osteoid calcifies to form new lamella and a blood vessel will grow into the tunnel to supply the cells.
Osteoblasts deposit layer upon layer of new concentric lamellae on the wall of the tunnel to fill it in. Some osteoblasts get trapped and become osteocytes
When the tunnel is reduced to size of normal Haversian canal, remaining osteoblasts die or become osteogenic cells part of the resting endosteum.
What is the cement line
This is the junction between the closests to outer surface lamella of the new osteon and the pre existing older bone. It is filled with GAGs which are glue between old and new bone.
What is the closing cone
The active area of osteoblasts depositing new layers of concentric lamellae behind the cutting cone front of osteoclasts.
