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BVM1 - Locomotion > 1.7 Tissue and bone adaptation > Flashcards

1.7 Tissue and bone adaptation Flashcards

1
Q

What makes a connective tissue?

A 
Extracellular matrix (ECM) = network of discreetly secreted macromolecules which maintain cell/tissue integrity 
Rich in fibrous proteins 
Glycoaminoglycans (GAG) - polysaccharides which usually link with proteins - proteoglycans
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2
Q

What are properties of hyaluronan/hyaluronic acid?

A

GAG,

  • very large molecule
  • high affinity for water (hydrophilic)
  • tissue viscosity
  • excellent lubricative properties
  • important in tissue repair/linked to tumour progression
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3
Q

What are properties of Chondroitin sulphate/keratan sulphate?

A

Highly charged sulphate groups provide electrostatic repulsion and high anti compressive properties

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4
Q

What is elastin?

A

Protein with a coiled structure

  • cross links between molecules
  • give elastin its characteristic elastic properties
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5
Q

What is Collagen?

A

Major component of ECM
Triple helix of polypeptide chains to form collagen microfibril
microfibril - fibrils - fibres
- high tensile strength
- complaint - arrangement of fibrils and CRIMP
- 29 forms

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6
Q

Describe the structure of a tendon

A 
Collagen - predominantly type I - 86%
Proteoglycans 1-5% 
Elastin 2% 
Cells: tenocytes (specialised fibrocytes)
Water
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7
Q

Describe the structure of a ligament

A

Fibrocytes plus ECM
Similar to tendon but lower (~75%) collagen component, more proteoglycan
Slight differences in collagen types/organisation

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8
Q

Describe the composition of cartilage

A

Cells = chondrocytes
Collagen ~ 10-20%, type II mostly (90%), but also III, IV XII and XIV
Predominant proteoglycan (10-20%) is chondroitin sulphate
Hylauronan
68% water
Regional variation

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9
Q

Describe the structure of a chondrocyte

A

Spheroid in shape - except surface
Synthesise type II collagen, large proteoglycan aggregates and non - collagenous proteins
Depend on anaerobic metabolism
Mechanical joint loading influences the functions of chondrocytes

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10
Q

How is cartilage adapted in the superficial (tangential) zone?

A

85% collagen, orientated tangential to surface

Greatest ability to resist shear stresses

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11
Q

How is cartilage adapted in the middle (transitional) zone?

A

Transition between shearing forces of surface to compression forces in deep layer; collagen arranged obliquely
Composed largely of proteoglycans

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12
Q

How is cartilage adapted in the deep (radial) zone?

A

Collagen fibres attached radially (vertical) into the tidemark - distributes loads and resists compression: high PG content

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13
Q

What are osteocytes?

A

support and maintain bone structure

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14
Q

What are osteoblasts?

A

synthesise bone matrix

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15
Q

What are osteoclasts?

A

absorb bone

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16
Q

What is Wolff’s Law?

A

Stresses caused by ligaments and muscles = stresses on the tissue
- signals to osteocytes to stimulate/send signals to osteoblasts to produce greater bone tissue to resist that load + reduce stresses

17
Q

How are trabeculae orientated?

A

Not randomly orientated but are orientated along the axis of high stress and strain
- parallel to major axis of stress and strain to resist and even out the loading on the bone

18
Q

What if you continually stress a tissue?

A

Fracture, rupture or failure ‘ultimate’ stress and strain

19
Q

Describe the relationship of ECM and cells

A
  1. Matrix can influence cell shape, survival and proliferation
  2. Matrix influences cell behaviour by binding to cell surface receptors that activate intracellular signalling pathways
  3. Continuous turnover of ECM - matrix macromolecules degraded and resynthesised
20
Q

What is intramembranous ossification?

A
  • Mesenchymal cells (stem cells by de noro method) become osteoblasts which then secrete osteoid (bone precursor tissue, but due to no ECM surrounding it, it produces pre-mineralised matrix)
  • Osteoblasts trapped in mineralised matrix become osteocytes
21
Q

How do long bones form?

A

Long bones form from cartilage template

22
Q

Describe the process of long bone formation - intramembranous ossification

A

Perichondrium lays down bone on cartilage in diaphysis region (mesenchymal cells differentiate into bone precursor cells and lay down bony tissue, gets mineralised forms a collar around the long bone)

23
Q

Describe the process of long bone formation - endochondral ossification

A

Cartilage at centre of shaft degenerates; vascularisation; matrix becomes impregnated with calcium salts

24
Q

How do bones grow in length?

A

Elongating in the diaphysis region

  • cells increase in no. + size
  • hypertrophied cells = enlarged and either excrete a large amount of matrix or change fates
25
Q

Stages in bone growth at the growth plate

A
  1. Proliferation and maturation of cartilage cells
  2. Hypertrophy of chondrocytes
  3. Calcification of cartilage matrix
  4. Depolarisation of bone on cartilage template
  5. Organisation of bony trabeculae and their osteoclastic resorption
26
Q

How does the bone grow in girth?

A

More lamellae/osteons created as the bone widens

27
Q

What are nutritional influences on bone?

A

Dietary calcium and phosphate salts
Absorption depends on calcitriol - only made in the presence of vitamin D
Vitamins C,A,K and B12

28
Q

What are hormonal influences on bone?

A

Calcitonin and parathyroid hormone - calcium metabolism regulation
Insulin growth hormone, thyroxine - bone growth
Oestrogen - growth plate closure (testosterone); osteoblast activity

29
Q

What is bone modelling?

A

the process of bone shape change in response to the loads imposed

30
Q

What is bone modelling?

A

A lifelong cyclical process of bone removal and addition

31
Q

What is the cyclical process?

A

Osteoclasts form and attach bone to matrix

  • resorption = osteoclasts secrete enzymes which break down bone. Osteoclast apoptosis
  • reversal = Area is populated by osteoblasts
  • formation = osteoblasts synthesise organic matrix. Osteoblasts regulate mineralisation of matrix. Osteoblasts entombed in matrix become osteocytes

BVM1 - Locomotion (13 decks)

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