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
What are the 2 layers that make up the periosteum?
Outer fibrous layer and inner osteogenic layer
Where are interstitial lamellae found?
Between osteons
Describe the formation of a primary osteon
- Osteoblasts in active periosteum put down new bome forming ridges around blood vessels
- Ridges fuse (periosteum now endosteum)
- Osteoblasts build bone inwards towards the centre of the canal
- Bone continues to grow outwards as osteoblasts place circumferential lamellae
Describe the formation of a secondary osteon
- Osteoclasts form and gather in an area that needs remodelling
- Osteoclasts begin to bore through existing bone creating tunnel inside bone - cutting cone
- Osteoblasts move into newly formed tunnel and deposit osteoid/build concentric lamellae layers slowly filling tunnel in - closing cone. Some osteoblasts are trapped and become osteocytes
- Eventually tunnel is reduced to size of typical haversian canal and osteoblasts lining the tunnel either die or revert back to osteogenic cells making up resting endosteum
What are the percentages of compact bone and spongy bone in long bones?
90% compact, 10% spongy
What component of mature bone are osteoclasts often found on and why?
Trabeculae as spongy bone can grow 5x faster than compacts bone - good Ca2+ source
Where is spongy bone predominantly located in long bones?
Epiphysis
What is the main function of spongy bone?
Support stress from multiple directions
Where is compact bone predominantly located in long bones?
Diaphysis
What is the main function of compact bone?
Support and protection
What is the location of blood supply for spongy bone?
Blood vessels between trabeculae
What is the location of blood supply for compact bone?
Blood vessels running through volkmanns and haversion canals
Why are not all osteons primary?
There are not enough blood vessels for osteons to form around
What is the cement line?
Line between newly formed secondary osteon and old bone
What is the rate of bone resorption of the cutting cone?
1mm/20 days
Approximately what percentage of our skeleton do we replace every year?
10%
What is the unit of spongy bone?
Trabeculae
What is the direction of unit growth in spongy bone?
Outwards
What is the unit of compact bone?
Osteon
What is the direction of unit growth in compact bone?
Inwards
What percentage of connective tissue in bone is crystallised mineral salts?
50-60%
What do tendons connect?
Muscle to bone
What do ligaments connect?
Bone to bone
What are the 3 main functions of joints?
Movement
Force transmission
Growth
What is a joint?
Any point at which 2 or more bones interconnect
What are the 3 functional classifications of joints?
Synarthrosis, amphiarthrosis, diarthrosis
What are synarthrosis joints?
Immovable, highly stable, common in axial skeleton, for growth and force transmission
What are amphiarthrosis joints?
Slightly moveable, medium stability, common in axial skeleton, e.g. intervertebral disks, force transmission
What are diarthrosis joints?
Freely moveable, low stability, common in the appendicular skeleton
What percentage of diarthrosis joints are found in the appendicular skeleton?
80%
What functional class of joint are synovial joints?
Diarthrosis
What is the most common type of joint?
Synovial
What are the 4 common features of synovial joints?
Articular cartilage, articular capsule, joint cavity, synovial fluid
What is the thickness of articular cartilage?
1-7mm
What type of cartilage is articular cartilage?
Hyaline (specialised)
What percentage of articular cartilage is cells?
5%
What is the articular cartilage attached to?
Bone
What are the functions of articular cartilage?
Protect ends of bones, absorb shock, support heavy loads for extended time periods, provide smooth and frictionless surface when combined with synovial fluid
What cells are found in articular cartilage?
Chondrocytes
Describe the cells in articular cartilage
Chondrocytes which build, repair and maintain cartilage
Live in lacunae
Live by themselves or in nests (depending on zone)
Secrete ECM
What percentage of articular cartilage is ECM?
95%
What 3 components make up the ground substance of the ECM in articular cartilage?
Water (+soluble ions), GAGS and PGs
What fibre is present in the ECM of articular cartilage
Collagen - type 2
What makes up the fixed solid component of articular cartilage?
PGs and Collagen fibres
What percentage of the wet weight of articular cartilage is water?
75%
What percentage of the dry weight of articular cartilage is collagen?
75%
What percentage of the dry weight of articular cartilage is PGs?
25%
What provides the swelling and hydrating mechanism for the proper function of articular cartilage?
GAGs
What are 3 of the common GAGs found in articular cartilage?
Hyaluronic acid, chondroitin sulphate, keratin sulphate
What is the common PG found in articular cartilage?
Aggrecan
What are the 3 zones that make up the functional zone of articular cartilage?
Surface, middle and deep zones
What zone of articular cartilage has the lowest PG level?
Surface zone
What zone of articular cartilage has the highest PG level?
Deep zone
What are the infoldings of the synovial membrane called?
Vili
What is the junction between calcified cartilage and subchondral bone called?
Osteochondral junction
What are thicker sections of the fibrous capsule called?
Capsular ligaments
How are the chondrocytes in cartilage nourished?
By diffusion
Where is the nearest blood supply to the articular cartilage?
In the articular capsule
What is unloaded equilibrium?
When the swelling force = the tension force
What is loaded equilibrium?
When the cartilage stops shrinking after load has been placed on it
What is the fluid loss out of cartilage due to load known as?
Creep
What are the 2 layers of the synovial membrane?
Intima & subintima
What are the 2 layers of the articular capsule?
Outer fibrous layer and inner synovial membrane
What does the synovial membrane line?
All non-articular surfaces in joint cavity
What is the synovial membrane made of?
Loose connective tissue
What is the fibrous capsule made of?
Dense connective tissue (irregular & regular)
What cells make up the intima layer of the synovial membrane?
Synoviocytes
What do proprioceptors do?
Monitor stretch and help us know the positions of our joints
What do synoviocytes secrete?
Hyaluronic acid and lubricating proteins
What does synovial fluid consist of?
Ultrafiltrate of blood plasma, hyaluronic acid, lubricating proteins, free cells (mono, lymph, macro, synovio)
What are the functions of synovial fluid?
Shock absorption, joint lubrication, chondrocyte metabolism, joint maintenance
Which is the larger GAG: keratin sulphate or chondroitin sulphate?
Chondroitin (125 units)
What is the max volume of synovial fluid in the joint cavity?
2ml
What does the tide mark indicate?
The boundary between the deep zone and calcified cartilage
What is the outer fibrous layer of the articular capsule continuous with?
Periosteum of bone
What is the most vascular layer of the articular capsule?
Subintima of the synovial membrane
What percentage of body mass is skeletal muscle?
40-50%
What are the 5 main functions of muscle?
Movement, stability, communication, control of body passages and heat production
What is the junction between bone and tendon called?
Osteotendinous junction
What is the junction between muscle and tendon called?
Myotendinous junction
What are the layers of skeletal muscle in order from outer to inner?
Epimysium -> perimysium -> fascicle -> endomysium -> myocyte -> sarcolemma -> sarcoplasm -> myofibril
What does the epimysium surround?
The entire muscle
What does the perimysium surround?
Fascicles
What are the epimysium and perimysium both made of?
Dense irregular connective tissue
What is a fascicle?
Buncle of myocytes
What does the endomysium surround?
Myocytes
What surrounds myocytes?
Endomysium
What is endomysium made out of?
Loose, irregular CT
What contains the nerve and blood vessels supplying myocytes?
Endomysium
What does a myofibril contain?
Sarcomeres
What does a myocyte contain?
Sarcolemma, sarcoplasm, myofibrils
What is the thickness range of myocytes?
10um -> 100um
What does the sarcoplasm contain?
Mitochondria, myoglobin, glycogen
What are deeper walls of deep fascia called?
Investing fascia
What is deep fascia between 2 bones called?
Interosseous membrane
What is deep fascia between muscles called?
Intermuscular Septa
What is deep fascia made of?
Dense irregular and regular CT
What is the outermost layer of muscle?
Epimysium
What is hypertrophy?
Increase in muscle size due to increased number of individual myofibrils inside myocytes
What are anabolic steroids?
Synthesized variants of testosterone
What are 2 ways hypertrophy can occur?
Resistance training and anabolic steroids
What are some of the side effects of anabolic steroids?
Acne, hair loss/growth, liver failure, shrivelled testes, infertility, mood swings, increased risk of coronary artery disease
What is atrophy?
Decrease in muscle size due to reduction of myofibrils in myocytes
What causes atrophy?
Lack of stimulation of muscle by motor neurons
At what age does muscle loss become accelerated?
50
What percentage of muscle is lost by 80 years?
40%
At what age does normal muscle loss begin?
20
What is hypoplasia?
Myocyte loss
How are myocytes created?
Fusion of many myoblasts during fetal growth
Myocytes contain many nuclei so are a…….
Syncytium
How are satellite cells made?
Formed from unfused myoblasts
Where are satellite cells located?
Outside the sarcolemma but within the basement membrane of myocytes
What is the role of satellite cells?
Divide upon signal and fuse to form new myocytes to repair damage
What are the 4 functions of skeletal muscle CT?
Organisation/scaffolding
Medium for blood vessels and nerves
Prevent excessive stretching
Distribute forces generated by contraction
What protein helps to align sarcomeres between myofibrils?
Desmin
What is the role of desmin?
To align sarcomeres between adjacent myofibrils
How do the Z lines of the outermost myofibrils attach to the sarcolemma, basement membrane and enomysium?
Via protein complexes
What are the protein complexes in myocytes responsible for?
Attaching myocytes and surrounding connective tissue
Strengthing the sarcolemma
