Musculoskeletal Flashcards
What are the 2 double meanings of bone?
Organ and tissue
What are the 6 functions of the skeletal system?
Support, protection, movement, calcium and phosphorus storage, haemopoiesis, fat storage
What percentage of the body’s calcium is found in bone?
90%
Where is the majority of red bone marrow located?
Around the axial skeleton
Where is the majority of yellow bone marrow located?
Around limbs/further from the centre of the body
What is the main function of the axial skeleton?
Support, protection and haemopoiesis
What is the main function of the appendicular skeleton?
Movement and fat storage
What are the 3 regions of long bones?
Epiphysis, metaphysis and diaphysis
How many axial bones are there?
80
How many named bones are there in the body?
206
How many appendicular bones are there?
126
What are the layers of bone from outer to inner in the diaphysis?
Periosteum, compact bone, endosteum
What are the layers of bone from outer to inner in the epiphysis?
Articular cartilage, compact bone, spongy bone
What is the centre of bone called?
Medullary cavity
What is spongy bone made of and what covers it?
Trabeculae, completely covered by endosteum
What connects the periosteum to the compact bone?
Perforating/Sharpays fibers
What 2 components make up ECM?
Fibres and ground substance
What type of fibres are found in bone?
Collagen
What do collagen fibres resist in bone?
Tension (stretching/pulling)
What is the ground substance in bone made up of?
Hydroxyapatite
What are the 4 cells that makeup bone in order from youngest to oldest?
Osteogenic cell, osteoblast, osteocyte, osteoclast
What does the ground substance in bone resist?
Compression (squeezing/crushing)
Where are osteogenic cells located?
On the surface of bone in the periosteum and endosteum, also found in central canals of compact bone
What is the function of osteogenic cells?
Normally dormant but can divide and supply developing bone with osteoblasts
Where are osteoblasts located?
In the layer under the periosteum or endosteum - wherever new bone is being formed
What is the function of osteoblasts?
Synthesis, deposition and calcification of osteoid (the ECM)
What is calcification?
When the osteoid becomes infiltrated with bone salts (hydroxyapatite)
What is the osteoid, and what does it consist of?
The ECM of bone/precursor matrix mainly consists of collagen (70%), also proteoglycans, proteins and water
Where are osteocytes located?
Within lacunae
What is the function of osteocytes?
Bone tissue maintenance, repair, Ca2+ exchange
Where are osteoclasts located?
At sites where bone resorption is occurring
What is the function of osteoclasts?
Secrete acids and enzymes, dissolve the mineral and organic components of bone
What does the medullary cavity contain?
Bone marrow
What is the endosteum?
Thin, inner fibro cellular layer lining the medullary cavity and trabeculae
What does the periosteum contain?
Blood vessels and nerves
What is the periosteum?
Outer, fibro cellular sheath which surrounds bone
What is the diaphysis made of?
Periosteum, compact bone, endosteum and medullary cavity
What type of force are trabeculae arranged to resist?
Perpendicular force
What is the epiphysis made up of?
Articular cartilage, compact bone, spongy bone, endosteum
What are perforating/sharpays fibres made of?
Thick bundles of collagen
What are the 2 components of all connective tissue?
Cells and ECM
What is the organic component of bone connective tissue?
Fibres - collagen type 1
What is the inorganic component of bone connective tissue?
Ground substance - hydroxyapatite
What is the osteoid?
The organic ECM (collagen) of bone initially laid down by osteoblasts prior to calcification
Overall, what force does the ECM of bone resist?
Torsion
What percentage of the osteoid is collagen?
70%
What makes up the osteoid layer?
Collagen, proteoglycans, proteins and water
What is a lacunae?
Small space in bone containing osteocyte
What does the acid secreted by osteoclasts dissolve?
Mineral components of bone e.g. hydroxyapatite
What are canaliculi?
Small canals through which osteocytes communicate with neighbouring cells using their long cellular processes
How do osteocytes communicate with other cells?
Through cellular processes running thorugh canaliculi
In what order do osteoclasts dissolve bone (organic or inorganic first)?
Inorganic hydroxyapatite then collagen fibres
What do the enzymes secreted by osteoclasts dissolve?
Organic component of bone e.g. collagen
What is the name of the ‘pit’ formed under osteoclasts after the bone is dissolved?
Howships lacunae
What is the ‘clear zone’?
Area/microbiome under osteoclast that ensures acid doesn’t escape and helps to anchor the cell
How long do osteoclasts live for?
2-3 months
What is thicker - the endosteum or periosteum?
Periosteum
How does bone grow?
Via appositional growth
Describe the process of appositional growth
- Signal triggers osteogenic cells to divide, resulting in some of the daughter cells being pushed into the matrix and becoming osteoblasts
- Osteoblasts lay down osteoid and calcify it
- Some osteoblasts become trapped in lacunae, eventually forming osteoclasts
- When growth stops, osteoblasts convert back to osteogenic cells or die - peri/endosteum goes back into resting state
Describe the process of bone resorption.
- Monocyte precuser cells leave BV and start to fuse on bone surface forming syncytium/osteoclase
- Osteoclasts start dissolving bone
- Osteoclasts eventually die via apoptosis
- Blood vessels grow into newly formed space in bone
What is the other type of growth that occurs in the body that bone cannot undergo?
Interstitial growth
Why can bone not grow via interstitial growth?
Because it is required to resist deformation
What 2 processes make up ‘bone remodelling’?
Appositional growth and bone resorption
How do long bones grow in length?
Endochondral ossification
Why can the epiphysis not undergo appositional growth?
Because it is covered in articulate cartilage
Describe endochondral ossification
- Chondrocytes in the hyaline cartilage in the epiphyseal plate divide (interstitial growth), growing the cartilage and pushing the epiphysis away from the metaphysis.
- Cartilage eventually dies, and osteoblasts place new bone as the ossification rate catches up to the cartilage growth rate
Where is the epiphyseal plate located?
Between the epiphysis and metaphysis - closes during puberty
What are the 2 types of bone?
Immature/woven & mature/lamellar
What are the 2 classes of mature bone?
Spongy (cancellous/trabecular) and Compact (cortical)
When is immature/woven bone seen?
Fetus - 3 years old and when a bone is quickly regrown e.g. broken arm
How does immature bone differ from mature bone?
Lower cell count, less dense, irregular collagen fibres
How is bone arranged in mature bone?
In sheets/layers called lamallae
What is the max width of an osteon or trabecula?
0.4mm
What is the max width of circumferential lamellae?
0.2mm
What are the 3 different organisations of lamellae in compact bone?
Circumferential, concentric and interstitial
Where are concentric lamellae found?
Osteons
Where are circumferential lamellae found?
Around the outer edge of the bone
What is the canal in which blood vessels run from the periosteum to central haversian canals?
Perforating/volkmanns canal