MSK L5 Bone and Cartilage Flashcards Preview

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Flashcards in MSK L5 Bone and Cartilage Deck (57):
1

Matrix: Made up of

Inorganic/mineral
Organic

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Matrix: Inorganic/mineral made up of

Hydroxyapatite

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Matrix: Inorganic/mineral Function

Compression strength
→ without = bendy

4

Matrix:Organic made up of

Collagen and proteoglycans
→ without =brittle bones (osteogenesis impracta

5

Matrix: Organic part function

Flexible strength

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Bones types:

1. Cortical or compact – more dense
2. Cancellous (trabecular or spongy) – less dense – bars and plates interconnected

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Matrix

Made up of many osteons

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Osteon

Concentric layers of lamellae around central blood vessels.

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Haversian canal

Contains blood vessels

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Interstial lamellae

In between two osteon

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Circumferential lamellae

Near matrix at surface

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Canaliculi

Radiate from lacunae from mature bones and osteocytes into the haversian canal. Channels provide passageway through compact bone to provide nutrition to the cells.

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Volkmann’s canal

Perforating blood vessels – allows them to join in outer membrane

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Osteoblast

Forming bone (multinucleated)

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Canaliculus

Radiate from lacunar of mature bone cell (osteocyte) into adjacent cavities with blood vessels to obtain nutrients.

16

2 types of bone development (ossification):

1. Intramembranous → ossification of membrane to bone
2. Endochondral ossification→ calcification of cartilage model into bone

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Bone Growth:

Apposition growth
Process (width)
Endochonral growth (length) process

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Apposition growth
Process (width)


1. OB in periosteum secrete matrix and become trapped as osteocytes
2. Osteoclasts in crease diameter of medullary cavity
3. Increases diameter of bones until skeletal maturity

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Endochonral growth (length) process

1. Requires interstitial growth from cartilage first
2. Occurs at epiphyseal growth plates
3. Stops when growth plates ossify

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New bone laid down

Woven bone (random collagen)

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Remodelled why

More orderly collagen fibres

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Remodelling process

Osteoblasts lay down bone
Osteoclasts resorbed (remove) bone
→ Lamellar bone (ordered formed)

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Mature bone

Old bone is constantly being replaced by new bone
Bone shape changes in response to changing stresses

24

Factors influencing bone growth and remodelling:

1. Mechanical factors
2. Genes
3. Hormones
4. Aging
5. Diseases

25

Mechanical → influencing bone growth and remodelling:

Wolf’s Law
→ More stress increases osteoblasts activity → more bone
→ Less stress decreases osteoblast activity → less bone

26

Genes: influencing bone growth and remodelling:

1. Determine potential shape and size
2. Height and bone mass is multifactorial (many genes involved and other factors)
3. Genes influence
a. Growth hormone release
b. Hormone receptor on bone cells
c. Ability to absorb nutrients from the gut
4. Some genetic disorders influence bone growth e.g. dwarfism (FGFr3 mutation), turners syndrome

27

Hormones: influencing bone growth and remodelling:

1. Growth, sex and thyroid hormones influence cell differentiation and metabolism
2. Overactive pituitary gland →excess GH

28

Ageing: influencing bone growth and remodelling:

1. Osteoblast matrix production slows in comparison to osteoclast matrix resorption
2. Decreased collagen deposition results in more brittle bone (less flexible strength)
3. Bone mass peaks at 25-30 years then falls.

29

Diseases: influencing bone growth and remodelling:

1. Osteoporosis → bone mass is reduced particularly in women after menopause (reduced oestrogen production).
2. Other factors affecting oestrogen levels
a. Removal of ovaries
b. Extreme exercise
c. Anorexia nervosa
d. Smoking
3. Cancellous bone is most affect as it is severly weakened if connections lost.


30

FGFr3 →

normal proliferation of chondrocytes
Defective = poor proliferation of chondrocytes an abnormal growth of long bones in limb.


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Cartilage: types

1. Fibrocartilage – strongest and most rigid
a. E.g. minicus
2. Hyaline cartilage
a. Joint surface
b. Epiphyseal growth plate
3. Elastic cartilage → balance between structure and flexibility
a. E.g. ear
b. Eustacian tube

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Cartilage growth

1. Appositional growth
2. Interstial growth

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Perichondrium: Outer layer

Dense irregular CT with fibroblasts

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Perichondrium: Inner layer

Fewer fibres with chondroblasts

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Perichondrium: Appositional growth

Chondroblasts

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Perichondrium: Interstial growth

Chondrocytes

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Articular Cartilage: Type of

Hyaline cartilage

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Articular Cartilage: Found

On articular surfaces of bones

39

Articular Cartilage:Has no

Perichondrium- as it forms part of the joint.

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Articular Cartilage: Growth

Similar to growth plate (but never ossifies)
Columns of cells → calcified cartilage and then form bone

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Articular Cartilage: Collagen structure

Arcades – high concentration of collagen on the surface.

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Articular Cartilage: Arcades

Type II collagen fibrils anchor proteoglycan matrix to bone

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Articular Cartilage: Growth stops

At a similar time to growth plate but never ossifies

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Function of Articular cartilage: Smooth

1. Reduces friction (heat → protein damage)
2. Low-wear surface

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Function of Articular cartilage: Deformable and elastic

Distributes load evenly
• Increased surface area → reduced force (peak contact stress)
• Creep (deformation and load) also increase surface area during sustained loading

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Function of Articular cartilage: Visually

• Simple, inert tissue
• Has high stiffness to compression and resilience
• Exceptional ability to distribute load and great durability

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Function of Articular cartilage: Adult articular cartilage

Hypocellular
Aneural
Avascular

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Cartilage matrix

. Large number of proteoglycans attaching to hyaluronic acid chain → help to maintain the reversible deformity property of cartilage.
→ Maintains water within the structure
3. Collagen type II (mainly)
a. Provide stable structure
4. Collagen (other types)

49

Matrix Synthesis Promotion

TGF
IGF

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Matrix Synthesis Inhibition

IL-1
TNF

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Matrix degradation Promotion

IL-1
TNF

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Matrix degradation Inhibition

TGF
IGF

53

Factors influencing cartilage metabolism

1. Mechanical factors
2. Injury
3. Aging
4. Diseases

54

Mechanical → adaptive remodelling

Cartilage is poor at this
➢ High strain = deposition
➢ Low strain = resorption
1. Anabolic and catabolic processes adjusted to adapt matrix to mechanical demands.
2. Low below 1 MPa may be catabolic while load above 1 MPa may be a anabolic stimulus.

55

Injury and repair:

1. Lack capillaries within cartilage.
2. Nutrients from diffusion (synovium not bone).
3. Chondrocytes do not normally divide in adult but still secrete matrix (repairs normal wear).
4. Tears/lesions never fully heal.

56

Ageing:

1. Decreased PG and collagen turnover
a. Collagen disruption
b. PGs lost
c. Water lost on compression
d. Tissue damage
2. Increase no-enzymatic glycation NEG)
3. Impaired joint lubrication
a. Friction/heat
b. Fibrillation
c. Osteoarthritis

57

Non-enzymatic glycation:

1. Cross-linking between collagen and sugars
2. Process not controlled by enzymes or cells
3. Advanced glycatino end=products (AGEs) make tissue stiffer, more brittle and yellowish (seen with ageing)

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