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Year 1 Locomotion > Bone structure, formation, growth and repair > Flashcards

Bone structure, formation, growth and repair Flashcards

1
Q

Give 5 roles of bone as a connective tissue

A

Structural support

Metabolic support

Cell adhesion

Medium of exchange

Defence, protection and repair

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2
Q

What are the two components of connective tissue? Give examples of each

A

Cells

Fibroblasts, Adipocytes and osteocytes

Extracellular matrix

Fibrous protiens - collagen/elastin

Ground substance - proteoglycans and glycoprotiens

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3
Q

What are the two main features of bone?

What gives these properties?

A

Rigidity - Mineralised ECM

Resilience - Type 1 collagen fibres

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4
Q

What are the main functions of bone?

A

Movement

Mineral Homeostasis

Support

Protection

Site of haematopoiesis

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5
Q

What is the Periosteum?

A

A non-calcified dense irregular connective tissue layer covering bone where tendons and ligaments insert.

Absent on surfaces covered by articular cartilage and around sesamoid bones (e.g. patella).

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6
Q

What does the periosteum consist of?

A

Consists of two layers: outer fibrous layer and inner cellular layer (contains osteoprogenitor cells and osteoblasts).

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7
Q

What is the role of the periosteum?

A

Helps bones grow in thickness (as it contains osteoprogenitor cells and osteoblasts)

Helps protect the bone

Assists in fracture repair

Helps nourish bone tissue

Is an attachment point for tendons and ligaments.

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8
Q

What is woven bone?

A

Immature/primary bone

First bone formed at any site. Occurs at sites of fracture healing

Collagen fibres arranged randomly.

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9
Q

What is Lamellar bone?

A

Mature bone

Collagen fibres remodelling into an orderly arrangment

Results in strong bone

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10
Q

What is cortical bone (compact) made up of?

A

Lamellae =

Bony plates made up of collagen fibres arranged in parallel

Outer circumferential lamellae

Haverian Systems (osteons)

Interstitial lamellae =

A result of bone remodelling and formation of new Havarsian systems

Inter-circumferntial lamellae

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11
Q

What is a Havarsain system (osteons)?

How does the Havarsian system work?

A

Concentric lamellae form around a Haversian Canal

Haversian Canals contain blood vessels, lymphatic vessels and nerves

Volkmans Canals run transversly or obliquely to the Haversian canals, allowing communication between Haversian canals, the periosteum, the marrow cavity and itself

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12
Q

What is Trabecular bone?

A

Cancellous/Spongey bone

A three dimensional network of beams and struts of lamellar bone - orientated along the lines of stress

Contain large areas of intercommunicating marrow spaces for haematopoesis

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13
Q

What are the 4 main arteries that supply the bone? State which part of the bone each artery supplies

A

Epiphyseal artery

Epiphysis region

Metaphyseal artery

Metaphysis region

Periosteal artery

Diaphysis region

Nutrient artery

Diaphysis region

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14
Q

Describe how bone cells are formed

A

Derived from mesenchymal stem cells

Differentiate into osteoproginator cells

Differentiate into osteoblasts

Osteoblasts line the bone and secrete organic bone matrix (osteoid) which is subsequently mineralised

Osteoid contains type 1 collagen, proteoglycans and glycoprotiens along with other protiens secreted by osteoblasts that aid in the mineralisation of the ECM

Differentiate into osteocytes

As osteoblasts are surrounded by matrix they become trapped and become osteocytes.

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15
Q

What are periosteal cells important in?

A

They are bone lining cells (resting osteoblasts)

Play an important role in fracture healing

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16
Q

What are osteocytes?

A

Mature bone cells that do not divide

They occupy the lacunae surrounded by bone matrix

Has roles in mechanotransduction and matrix maintenance

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17
Q

How do osteocytes carry out their role of mechanotransduction?

A

Dendritic processes of osteocytes pass through canaliculi which radiate from lacunae

The dendritic processes then anastomose with those from other lacunae allowing signals to be passed

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18
Q

How do osteocytes carry out their role of matrix homeostasis?

A

Gap junctions between dendritic processes of osteocytes allow transfer of ions and nutrients

19
Q

What are osteoclasts?

A

Large multinucleated cells with a ruffled border (aids with bone reabsorption)

Derived from the monocyte-macrophage system

20
Q

What role do osteoclast play?

A

Involved in bone remodelling, growth and repair

Main role is reabsorption of the bone matrix - sysnthesise and secrete enzymes and acid

Form Howship’s lacunae (reabsoption craters)

Nutrients is reabsorbed back into the blood

21
Q

Describe the normal bone remodelling cycle

A

Continual process throughout life in response to mechanical stress or microfractures of the bone

Coupling of bone resorption and formation

Resorption

Osteoclast apoptosis and removal

Reversal

Osteoblast recruitment, differentiation and activation

Results in matrix synthesis

Formation

Mineralisation

Quiescence

Osteoclast recruitment, differentiation and activation

RETURNS TO RESORPTION

22
Q

Describe how in normal cortical bone remodelling, new Haversian systems are replaced and remodelled

A

Osteoclasts form cone shaped tunnels into the compact bone (resorption cavities).

The tunnels then become invaded by blood vessels, osteoblasts and osteoprogenitor cells.

Osteoblasts lay down new bone in concentric lamellae around blood vessels forming new Haversian systems (closing cone).

23
Q

How is normal bone remodelling regulated?

What can alter this system

A

Differentiation of osteoclasts is regulated by signalling molecules secreted by osteoblasts

RANKL

Binds to RANK on osteoclasts and causes activation

Osteoprotegerin (OPG)

Non-signalling decoy receptor of RANKL

Results in less osteoclast activation as less RANKL binding to RANK

This system can be altered by cytokines, hormones, and drugs. Balance of RANKL to OPG is important in determining the degree of resorption

24
Q

Name the two processes that bone develops by

How do these processes differ?

A

Intramembronous ossification

Mesenchyme –> Bone

Endochondral ossification

Mesenchyme –> Cartilage –> Bone

25
Q

Describe the process of intramembranous ossification.

Where would this process occur?

A

Direct replacement of mesenchyme by bone tissue without a cartilage precursor

Membrane of mesenchyme which differentiates directly into osteoprogenitor cells –> osteoblasts –> secrete osteoid which is then calcified.

This region is known as the primary ossification centre.

Blood vessels invade. A sponge-like trabeculae is established and vascular connective tissue is transformed into bone marrow.

Occurs in flat bones of the skull, clavicle and mandible

26
Q

What are the two main steps in endochondrial ossification?

Where is this process likely to occur?

A

Miniature hyaline cartilage model is formed

Cartilage model continues to grow, providing scaffolding bone developement. It is eventually resorbed and replaced by bone

Occurs mainly in weight bearing bones eg. long bones, vertebrae, pelvis etc.

27
Q

How is the primary ossification centre formed in endochondral ossification?

A
  1. Mesenchyme develops into chondroblasts which form a cartilage model
  2. Cartilage cells in the centre of the diaphysis hypertrophy, die and become calcified –> leaves large open spaces in cartilage (future marrow cavity)
  3. Osteoblasts secrete matrix and form a subperiosteal bony collar
  4. Vascularisation of the perichondrium transforms it into periosteum
  5. Blood vessels invade cartilage model with osteoprogenitor cells
  6. Osteoprogenitor cells differentiate into osteoblasts
  7. Osteoblasts secrete bone matrix on surface of calcified cartilage
28
Q

What are the differences in formation of the secondary ossification centres compared to the primary ossification centres in endochondral ossification?

A

Occurs in the Epiphyses

Similar process to primary ossification centre formation

Osteoprogenitor cells invade the cartilage and differentiate into osteoblasts which lay down bone on cartilige scaffold

Except at articular surface and epiphyseal plate

No bony collar

29
Q

Compare the primary and secondary ossification centres

A

Primary :

Reside in diaphyses

Develop in foetal life

Secondary :

Reside in Epiphyses

Develop in after birth

30
Q

What is longitudinal bone growth?

A

Occurs at the epiphyseal growth plate of weightbearing long bones

Is the proliferation of cartilage cells followed by endochondrial ossification

Replacement by bone occurs at the diaphyseal aspect

Eventually the ossification zone overtakes proliferation and rest zones causing the epiphyseal growth plate to close

31
Q

What is appositional growth?

A

Growth in width of the bone

New bone is formed under the periosteum

32
Q

Name the zones and zone functions on the epiphyseal growth plate

A

Resting zone (quiescent zone/zone of reserve cartilage)

Cartilage cells found

Proliferation zone (zone of proliferation) Cartilage cells proliferation under influence of insulin-like growth factor which is produced by hepatocytes in response to growth hormone. Chondrocytes are stacked in columns like coins.

Hypertrophic zone (zone of maturation and hypertrophy)

Chondrocytes mature and hypertrophy

Calcification zone

Hypertrophied chondrocytes die and cartilage matrix is calcified. Osteoclasts remove calcified matrix.

Ossification zone

Osteoprogenitor cells invade and differentiate into osteoblasts which lay down bone on cartilage scaffold

33
Q

What is a fracture?

Give 3 examples of fractures

A

A breach in the integrety of part or whole of the bone

Transverse (straight across)

Crush (compression of bone)

Oblique (diagonally up)

34
Q

What are the 6 stages of fracture healing?

A
  1. Haematoma
  2. Granulation tissue
  3. Callus
  4. Woven bone
  5. Lamellar bone
  6. Remodelling
35
Q

Regarding fracture healing, describe what happens in the following stage:

Haematoma

A
  1. Rupture of vessels in region of fracture site causing haematoma to form
  2. Necrosis of bone fragments
  3. Initiates inflammatory reaction
  4. Phagocytes migrate to area to remove necrotic tissue
36
Q

Regarding fracture healing, describe what happens in the following stage:

Granulation tissue

A
  1. Blood clot is invaded by small capillaries and fibroblasts from surrounding connective tissue
  2. Granulation tissue forms
  3. Cytokines and growth factors induce cellular proliferation
37
Q

Regarding fracture healing, describe what happens in the following stage:

Callus

A
  1. Fibrous tissue, inflammatory cells and cartilage form a soft callus
  2. Forms a bridge between bone ends
38
Q

Regarding fracture healing, describe what happens in the following stage:

Woven bone

A

Osteoprogenitor cells proliferate and differentiate into osteoblasts to form woven bone

Strengthens the callus and gives rigidity (bony callus)

When callus is hard enough that no movement takes place, the fracture site is clinically united

39
Q

Regarding fracture healing, describe what happens in the following stage:

Lamellar bone

A

Gradually replaces woven bone

40
Q

Regarding fracture healing, describe what happens in the following stage:

Remodelling

A
  1. Osteoclasts and osteoblasts remodel lamellar bone in response to stresses
  2. Excessive callus is reabsorbed and medullar cavity re-established
41
Q

Give 3 factors that aid fracture healing

A

Stability of the fracture

Apposition of bone ends

Adequate blood supply

42
Q

Factors that delay fracture healing

A

Excessive movement of bone ends

Poor blood supply

Infection

Foreign bodies

43
Q

Define the following terms in regards to fracture healing:

  1. Malunion
  2. Delayed union
  3. Non-union
A
  1. Healing in unsatifactory positions
  2. Takes longer than expected to unite
  3. Can lead to fibrous union or pseudoarthritis

Year 1 Locomotion (18 decks)

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