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Block 4: Anatomy + Physiology > Bone structure, formation and growth > Flashcards

Bone structure, formation and growth Flashcards

1
Q

What type of tissue are bones?

A

Connective tissue

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2
Q

What are the constitutes of bone?

A 
Cells (esp. fibroblasts) 
Extracellular matrix (secreted by fibroblasts and made up of fibrous proteins e.g. collagen/ elastin and ground substance e.g. water glycoproteins and proteoglycans)
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3
Q

What makes up a proteoglycan?

A

Protein core with disaccharide units attached (disaccharide units = Glycosaminoglycans)

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4
Q

What is the role of glycoproteins in bones?

A

Help attach cells to extracellular matrix

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5
Q

What are the features of bones?

A

Rigidity (through mineralised ECM called hydroxyapatite)
Resilience (allows bones to return to original shape when deformed - prevents breaking - provided by collagen type 1 fibres)

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6
Q

What are the functions of bones?

A 
Movement
Mineral homeostasis
Support
Protection 
Site of haematopoeisis
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7
Q

What are the features of periosteum?

A

Non-calcified, dense, irregular connective tissue layer covering bones where tendons and ligaments insert
Consists of two layers: outer fibrous layer and inner cellular layer (containing osteoprogenitor cells and osteoblasts)

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8
Q

What are the functions of periosteum?

A 
Helps bones grow in thickness
Helps to protect bones
Assists in fracture repairs 
Helps nourish bone tissue
Attachment point for tendons and ligaments
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9
Q

Which bones do not have a periosteum?

A

Sesamoid bones (those that are entirely surrounded by tendons or muscles)

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10
Q

What are the microscopic features of woven bone?

A

Collagen fibres arranged randomly (meaning can be formed quickly but are relatively weak)
Found at site of fracture healing and in new bone formation

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11
Q

What are the microscopic features of lamellar bone?

A

Collagen fibres laid out in orderly arrangement to provide strength

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12
Q

What are the types of lamellar bone?

A

Cortical (found surrounding the shafts of diaphysis)
Trabecular (“spongey bone” - formed by beams and struts orientated along the lines of stress to redistribute force throughout bone)

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13
Q

What is lamellae?

A

Bony plates made up of irregularly arranged collagen fibres

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14
Q

What are the functions of Haversian systems (osteons)?

A

Arranged in parallel to long axis of bone to withstand force when its applied to either end of bone to reduce risk of bone bending or breaking
Can be remodelled in response to changes and stress (interstitial lamellae)
Made up of concentric lamellae surrounding central canal (containing blood vessels, lymphatics and nerves)

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15
Q

What are Volkmann’s canals?

A

Run transversely and allow communication between Haversian canals, the periosteum, the marrow cavity and each other

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16
Q

What are the features of trabecular bone?

A

3D network of beams and struts orientated along lines of stress
Areas of intercommunicating space filled with bone marrow (e.g. for haematopoiesis)
More likely to be remodelled in response to changes in stress

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17
Q

Where are osteoblasts formed from?

A

Osteoprogenitor cells (derived from mesenchymal stem cells)

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18
Q

What is the function of osteoblasts?

A

Secrete extracellular matrix (osteoid) - secreted in a non-mineralised form (and mineralised outside of the cell)
Secrete type 1 collagen, proteoglycans and glycoproteins
Secrete proteins that aid mineralisation of extracellular matrix (e.g. alkaline phosphatase)

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19
Q

What is raised ALP indicative of?

A

Liver problem or bone problem

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20
Q

What cells are formed from osteoblasts?

A

Osteocytes - once osteoblasts have been surrounded by matrix and matured

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21
Q

What are osteocytes?

A

Mature bone cells
Trapped in extracellular matrix in spaces called lacuna
Dendritic processes pass through canaliculi (from lacunae) and anastomose, gap junctions between dendritic processes transfer ions and nutrients between osteocytes

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22
Q

What is the function of osteocytes?

A

Matrix maintenance
Calcium homeostasis
Mechanotransduction (detect stress/ force and trigger action of surrounding bone cells)

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23
Q

What are osteoclasts?

A

Derived from monocyte-macrophage system
Large multi-nucleated cells with characteristic ruffled border that makes contact with bone
Occupy Howship’s lacunae (formed from reabsorbtion)

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24
Q

What are the functions of osteoclasts?

A

Synthesise and secrete enzymes and acid involved in breaking down and reabsorbing bone in a localised way
Important in remodelling, growth and repair

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25
Q

What is the basic bone remodelling cycle?

A

Osteoclasts reabsorb bone

Osteoblasts rebuild bone by synthesising and mineralising the matrix

26
Q

How is bone remodelling regulated?

A

RANKL (secreted by osteoblasts and binds to RANK receptors on osteoclasts to stimulate bone reabsorption)
Osteoprotegerin (OPG) - mops up extra RANKL to limit reabsorption

[Ratio of OPG to RANKL important in determining reabsorption rate]

27
Q

What is the role of oestrogen in bone remodelling?

A

Increases amount of OPG (thus favouring bone formation)

28
Q

What is mesenchyme?

A

Undifferentiated embryonic connective tissue

29
Q

What are the two methods of bone development?

A

Intramembranous ossification

Endochondral ossification

30
Q

What is intramembranous ossification?

A

Direct replacement of mesenchyme by bone tissue (so no cartilage precursor)

[e.g. flat bones of skull, clavicle, mandible]

31
Q

What are the steps of intramembranous ossification?

A
  1. Membrane of mesenchyme differentiate into osteoprogenitor cells and then into osteoblasts which secrete osteoid (which is then calcified) - PRIMARY OSSIFICATION CENTRE
  2. Blood vessels invade
  3. Trabeculae established and vascular connective tissue transformed into bone marrow
  4. Mesencyhme on outside differentiates into fibrous periosteum and bone cells form cellular layer of periosteum
  5. Compact bone formed deep to periosteum with trabecular bone in between
32
Q

What is endochondral ossification?

A

Bone develops on cartilage model

[Weight bearing bones e.g. long bones, vertebrae, pelvis]

33
Q

What are the steps of endochondral ossification?

A
  1. Mesenchyme develops into chondroblasts forming cartilage model
  2. Cartilage cells in centre of diaphysis hypertrophy, die and then become calcified (leaving large open spaces)
  3. Osteoblasts secrete matrix and form subperiosteal bony collar
  4. Vascularisation of perichondrium transforms it into periosteum
  5. Blood vessels invade cartilage model with osteoprogenitor cells which then differentiate into osteoblasts
  6. Osteoblasts secrete bone matrix on surface of calcified cartilage - primary ossification centre
  7. Similar process in epiphyses forms secondary ossification centre
34
Q

What is the difference in development between primary and secondary ossification centres?

A

Primary ossification centres develop in utero

Secondary ossification centres develop after birth

35
Q

What are the various types of bone growth?

A 
Longitudinal growth (at epiphyseal growth plate) 
Appositional growth (growth in width)
36
Q

How does longitudinal growth occur?

A

Cartilage proliferation at epiphyseal aspect
Replacement by bone at diaphyseal aspect
Eventually growth plate gets smaller and is replaced by bone causing marrow cavity of epiphysis and diaphysis to join up (once this has happened no further growth can occur)

37
Q

What is the clinical significance of longitudinal growth?

A

Relatively weak point in bone
Growth plate fracture (Salter-Harris fracture) can cause deformities in developing bone
Disorders affecting bone mineralisation (e.g. Rickets) can size and shape of growth plate

38
Q

What is a fracture?

A

Breach in the integrity of part or the whole of a bone

Many different types of fracture!

39
Q

What is a simple (closed) fracture?

A

Clean break with intact overlying tissues

40
Q

What is a compound (open) fracture?

A

Direct communication between broken bone and skin surface

41
Q

What is a transverse fracture?

A

Fracture line perpendicular to longitudinal axis

42
Q

What is an oblique fracture?

A

Fracture line angled approx. 30-45 degrees to longitudinal axis

43
Q

What is a spiral fracture?

A

Fracture line is oblique and encircles a portion of the shaft

44
Q

What is a comminuted fracture?

A

Multiple bone fragments

45
Q

What is a compression (crush) fracture?

A

Compression of trabecular bone (e.g. vertebral bodies)

46
Q

What is a greenstick (incomplete) fracture?

A

Bone incompletely fractured (portion of cortex and periosteum intact on compression side)

47
Q

What is a traumatic fracture?

A

Result of a single violent injury

48
Q

What is a stress fracture?

A

Result of repeated stress (e.g. in athletes)

49
Q

What is a pathological (secondary) fracture?

A

Fracture occurring in bone weakened by disease processes (e.g. metabolic, heraditary)

50
Q

What are the stages of fracture healing?

A
  1. Haematoma
  2. Granulation tissue
  3. Callus
  4. Woven bone
  5. Lamellar bone
  6. Remodelling
51
Q

What occurs during the haematoma stage of fracture healing?

A

Rupture of vessels in region of fracture causing haematoma leading to necrosis of bone fragments and initiation of inflammatory reaction - migration of phagocytes to remove necrotic tissue

52
Q

What occurs during the granulation tissue stage of fracture healing?

A

Blood clot invaded by small capillaries and fibroblasts from surrounding connective tissue to form granulation tissue. Cytokines and growth factors induce cellular proliferation

53
Q

What occurs during the callus stage of fracture healing?

A

Fibrous tissue, inflammatory cells and cartilage form a soft callus forming a bridge between bone ends

54
Q

What occurs during the woven bone stage of fracture healing?

A

Osteoprogenitor cells proliferate and differentiate into osteoblasts to form woven bone
Strengthens callus and gives rigidity
Fracture site clinically united when callus is sufficiently firm that movement no longer takes place

55
Q

What occurs during the lamellar bone of fracture healing?

A

Lamellar bone gradually replaces woven bone

56
Q

What occurs during the remodelling bone of fracture healing?

A

Osteoclasts and osteoblasts remodel lamellar bone in response to stresses
Excessive callus is reabsorbed and medullar cavity re-established

57
Q

What factors aid fracture healing?

A

Stability of fracture
Apposition of bone ends
Adequate blood supply

58
Q

What factors delay fracture healing?

A

Excessive movement of bone ends (instability)
Poor blood supply
Infection
Foreign bodies

59
Q

What is malunion?

A

Fracture healing in an unsatisfactory position

60
Q

What is delayed union?

A

Fracture taking longer than expected to unite

61
Q

What is non union?

A

Inadequate fracture healing leading to fibrous union or pseudoarthritis

Block 4: Anatomy + Physiology (12 decks)

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