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

Bone structure, formation, growth and repair Flashcards

1
Q

What are the 5 tissue types?

A

Epithelia, muscle, connective tissue, blood, nervous tissue

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2
Q

What are the 5 roles of connective tissue?

A
  • Structural support
  • Metabolic support
  • Cell adhesion
  • Medium of exchange
  • Defense, protection and repair
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3
Q

What components of bone contribute to its rigidity?

A

Mineralised ECM - hydroxyapatite (calcium and phosphate crystals)

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4
Q

What component of bone contributes to it’s resilience?

A

Type 1 collagen fibres

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5
Q

What are the 5 functions of bone?

A
  • Movement
  • Mineral homeostasis
  • Support
  • Protection
  • Site of haematopoiesis
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6
Q

What is periosteum? What are its functions?

A

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

  • Helps bones grow in thickness (as it contains osteoprogenitor cells and osteoblasts)
  • Helps protect the bone
  • Assists in fracture repair
  • Helps nourish bone tissue
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7
Q

Describe the microscopic appearance of woven bone

A

Woven bone (immature/primary bone) – first bone formed at any site. Collagen fibres arranged randomly. Occurs at sites of fracture healing ​

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8
Q

Describe the microscopic appearance of lamellar bone

A

Lamellar bone (mature bone) – collagen fibres remodelling into orderly arrangement -> STRENGTH​

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9
Q

Define lamellae

A

Lamellae = bony plates made up of collagen fibres arranged in parallel ​

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10
Q

Describe osteons/haversian systems

A

Concentric lamellae around a central canal (Haversian canals)​
Haversian canals contain blood vessels, lymphatic vessels and nerves ​
Volkmann’s canals run transversely or obliquely and allow communication between Haversian canals, the periosteum, the marrow cavity, and each other

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11
Q

Describe the stages a cell goes through to mature to an osteocyte

A

Mesenchymal stem cell –> osteoprogenitor cell –> osteoblast –> osteocyte

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12
Q

What do osteoblasts secrete?

A

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

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13
Q

What type of bone cell are periosteal cells and what are they important for?

A

Bone lining cells (periosteal cells) are resting osteoblasts – important role in fracture healing​

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14
Q

What does osteoid consist of?

A

Type 1 collagen, proteoglycans, glycoproteins and other proteins secreted by osteoblasts

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15
Q

What are the 3 functions of osteocytes?

A
  • Mechanotransduction
  • Matrix maintenance
  • Calcium homeostasis
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16
Q

What are osteoclasts derived from?

A

Derived from monocytes-macrophage system (haemopeoitic origin) ​

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17
Q

What do osteoclasts look like?

A

Large multinucleate cells with ruffled border

18
Q

Why is bone remodelling necessary?

A

Bone remodelling allows:​

  • Strength and shape of bone to be adjusted in response to patterns of stress and mechanical forces, or to repair microfractures​
  • Replacement of old organic matrix which degenerates and becomes brittle and weak
19
Q

Describe the bone remodelling cycle

A

Quiescence (nothing happens) -> Resorption (Osteoclast act) -> reversal (OC apoptosis and removal) -> formation (OB matrix synthesis)

20
Q

Describe intramembranous ossification

A

Direct replacement of mesenchyme by bone tissue
​-Membrane of mesenchyme differentiates directly into osteogenic cells​
-Osteoblasts cluster together and secrete organic bone matrix. This region is known as the primary ossification centre. ​
-The bone matrix becomes calcified ​
-The matrix develops into spongy/trabecular bone around the capillaries​
-The blood vessels eventually condense to form red bone marrow which fills the spaces in the spongy bone ​
-Mesenchyme on outside differentiates into fibrous periosteum and bone cells form cellular layer of periosteum​
-The most superficial layer of spongy/trabecular bone (deep to the periosteum) is transformed into compact bone

21
Q

Where does intramembranous ossification occur?

A

Flat bones of skull, parts of the clavicle, mandible and scapula

22
Q

Describe endochondral ossification

A

Bone develops on cartilage model.​
Steps of endochondral ossification:​
-Mesenchyme develops into chondroblasts
-Miniature hyaline cartilage model is formed​
-Cartilage model continues to grow, providing a scaffold for bone development. It is eventually resorbed and replaced by bone​

23
Q

In endochondral ossification, where do primary ossification centres form?

A

In the diaphysis of long bones - in foetus

24
Q

In endochondral ossification, where do secondary ossification centres form?

A

Secondary (epiphyseal) ossification centres form in epiphyses of long bones which develop at different times after birth. ​

25
Q

In endochondral ossification, in which direction does primary ossification occur?

A

Primary ossification proceeds inwards from the external surface to the centre of the bone

26
Q

In endochondral ossification, in which direction does secondary ossification occur?

A

Secondary ossification starts in the centre and proceeds outwards. his leaves an outer ring of cartilage around the epiphysis which will form the articular cartilage of the joint and the epiphyseal growth plate (between the epiphysis and the diaphysis) ​

27
Q

Describe longitudinal growth

A
  • At the epiphyseal growth plate ​
  • Proliferation of cartilage cells followed by endochondral ossification

Cartilage proliferation occurs at the epiphyseal aspect ​
Replacement by bone occurs at the diaphyseal aspect ​
Eventually ossification zone overtakes proliferation and rest zones -> epiphyseal growth plate closes ​

28
Q

Describe appositional growth

A
  • Growth in width ​

- New bone formed under periosteum

29
Q

Describe the 5 different zones of the epiphyseal growth plate

A

1) Resting zone (quiescent zone/zone of reserve cartilage) – scattered chondrocytes, low rate of proliferation, anchors epiphyseal growth plate to bone of epiphysis
2) Proliferation zone – cartilage cells are proliferating under influence of insulin-like growth factor which is produced by hepatocytes in response to growth hormone. Chondrocytes are stacked in columns like coins.
3) Hypertrophic zone – chondrocytes mature and hypertrophy, and secrete signalling molecules that encourage invasion of blood vessels. Eventually the cells undergo apoptosis and die.​
4) Calcification zone – Hypertrophied chondrocytes die and cartilage matrix becomes calcified. ​
5) Ossification zone – Osteoclasts remove calcified cartilage and osteoblasts lay done bone matrix

30
Q

What is the clinical significance of growth plates?

A
  • Relative weak point particularly if subject to shearing forces​
  • Fractures involving growth plate (Salter-Harris fractures) can cause deformities in developing bone​
  • Disorders affecting bone mineralisation, e.g. rickets, can affect size and shape of growth plate
31
Q

Define fracture

A

A fracture is a breach in the integrity of part or the whole of a bone

32
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

33
Q

What happens in the haematoma stage of fracture healing?

A
  • Necrosis of bone fragments ​

- Inflammatory response -> phagocytosis

34
Q

What happens in the ‘granulation tissue’ stage of fracture healing?

A
  • Capillaries and fibroblasts invade blood clot -> forms fibrovascular granulation tissue ​
  • Cytokines and growth factors induce cellular proliferation

Occurs within the first 2 weeks of fracture

35
Q

What happens in the ‘callus’ stage of fracture healing?

A
  • Fibrous tissue, inflammatory cells and cartilage form a soft callus (fibrocartilagenous callus)​
  • Forms a bridge between bone ends

The callus is very soft in the first 4-6 weeks of fracture healing and so the patient will need adequate support and bracing until the callus begins to ossify. ​

36
Q

What happens in the ‘woven bone’ stage of fracture healing?

A
  • Osteoprogenitor cells proliferate and differentiate into osteoblasts to lay down woven bone​
  • Strengthens the callus and gives rigidity (bony callus)​
  • When callus is sufficiently firm that movement no longer takes place the fracture site is clinically united ​
    ​
    Depending on the size of the bone and the fracture it can take up to 3 months for the fibrocartilagenous callus to be transformed into bone.
37
Q

What happens in the ‘lamellar bone’ stage of fracture healing?

A

Action of osteoblasts and osteoclasts gradually replaces woven bone with lamellar bone​

38
Q

What happens in the remodelling stage of fracture healing?

A
  • Osteoclasts and osteoblasts remodel lamellar bone in response to stresses ​
  • Excessive callus is reabsorbed and medullary cavity re-established
    Remodelling can take between 1 and 2 years.
39
Q

What 3 factors aid fracture healing?

A

1) Stability of the fracture​
2) Apposition of bone ends​
3) Adequate blood supply

40
Q

What 6 factors delay fracture healing?

A

1) Excessive movement of bone ends​
2) Bone loss/soft tissue trauma ​
3) Poor blood supply​
4) Infection ​
5) Foreign bodies​
6) Poor general health, poor nutrition, certain medications, smoking

41
Q

What is osteoprotegerin (OPG)

A

A non-signalling decoy of RANKL

42
Q

What activates osteoclasts?

A

RANKL secreted by osteoblasts

Locomotion (26 decks)

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