MS System - Bones

Question 1

What is bone?

Answer 1

• Collagen fibre framework
• In a mucopolysaccharide-rich gel
• Hardened by hydroxyapatite crystals

Question 2

Epiphysis

• where
• structure
• function

Answer 2

• Top of bone
• Top = articular surface w hyaline cartilage
• Movement, stability

Question 3

Diaphysis

• where
• structure
• function

Answer 3

• Middle of bone
• Outside = compact bone, inside = hollow cylinder (bone marrow)
• Where blood vessels enter

Question 4

Metaphysis

• where
• structure
• function

Answer 4

• Between epiphysis & diaphysis
• Plates of hyaline cartilage
• Region of growth

Question 5

Cancellous (trabecular) bone

• where
• structure
• function x2

Answer 5

• Both ends
• Porous, open structure
• Supporting strength
• Site of haemopoiesis

Question 6

Cortical (compact) bone

• where
• structure
• function

Answer 6

• Outside (forms shaft)
• Solid, compact
• stiffness, strength

Question 7

Periosteum

• where
• structure

Answer 7

• Outside of diaphysis

- Compact bone

Question 8

Trabeculae

Answer 8

Laid along lines of stress:

• Allows distribution of stress
• High SA for metabolism

Question 9

Loss of trabecular due to…

Answer 9

If bones aren’t stressed –> bones remodel –> lose trabeculae

Question 10

Haversian Canals

Answer 10

Blood vessels along the LONG axis

Question 11

Volkmann’s Cannals

Answer 11

Blood vessels along the PERPENDICULAR axis

Question 12

Lamellae

• what
• where

Answer 12

• Concentric circles around vessels

- Mainly in cortical bone

Question 13

Lamellae & osteocytes

Answer 13

Most cells are in v close contact to blood vessels, BUT osteocytes aren’t –> finger-like projections

Question 14

Cancellous bone & lamellae

- SO?

Answer 14

• Less lamellar layers
  SO
• Less dense & coordinated –> weaker

Question 15

Bone matrix components x3

Answer 15

• Collagen (organised arrangement)
• Hydroxyapatite
• Water

Question 16

What is hydroxyapatite?

Answer 16

Precipitated calcium phosphate crystals

Question 17

Osteoblasts

• function
• structure
• extra

Answer 17

• Bone builders
• Mononucleate
• Deposit collagen –> then hydroxyapatite

Question 18

Osteoclasts

• function
• structure
• extra

Answer 18

• Bone chewers
• Multinucleate
• Reabsorb bone by demineralisation:
  - forms ‘sealing zone’ –> protons & hydrolytic enzymes –> breaks down bone matrix –> releases Ca

Question 19

Osteocytes

• function x2
• formed

Answer 19

• Maintain matrix
• Relatively inactive
• Osteocytes become entombed in matrix/lacunae

Question 20

Osteoprogenitors

• where
• function

Answer 20

• Line bone surface

- Stem cells –> form osteoblasts

Question 21

Formation of woven bone

• when damaged…
• then…
• over time…

Answer 21

• Periosteum = damaged –> sends signals –> increased blood flow, inflammation
• Callus formation –> osteoblasts form ‘woven bone’ = weak
• Lamellular bone laid down

Question 22

Lamellular bone = stronger than woven bone as…

Answer 22

Woven bone –> collagen fibres = irregular

Lamellular bone –> collagen fibres = in sheets

Question 23

Wolff’s Law

Answer 23

Bone adapts to the load under which it is placed

Question 24

Bone remodelling/straightening

Answer 24

Side with more pressure remodels more –> bone can straighten

Question 25

Calcitonin

Answer 25

Less osteoclast activity --> lower blood Ca levels

Question 26

PTH | Parathyroid hormone

Answer 26

More ostoaclast activity --> releases Ca

Question 27

Bone remodelling (4 steps)

Answer 27

1) Quite (quiescence) 2) Osteoclasts --> demineralisation 3) Osteoprogenitors --> differentiate to osteoblasts 4) Osteoblasts --> lay down new bone

Question 28

Bone mass & menopause

Answer 28

Decreases faster --> as less oestrogen = more bone 'chewing'

Question 29

Chondroblasts

Answer 29

Form cartilage

Question 30

Chondroclasts

Answer 30

Remove cartilage

Question 31

Ossification

Answer 31

The process where cartilage is replaced by bone

Question 32

Centres of ossification: - primary - secondary

Answer 32

- Diaphysis | - Epiphysis

Question 33

Epiphyseal plate - what - where - structure

Answer 33

- Growth plate - Between epiphysis & diaphysis - Made of cartilage

Question 34

Growth stops when...

Answer 34

Epiphysis & diaphysis fuse | normally end of puberty

Question 35

Ossification process (5 steps)

Answer 35

1) Resting zone - Chondroblasts lay down cartilage (by epiphysis) 2) Growth zone - Chondroblasts --> mitosis 3) Hypertrophic zone - Differentiate --> chondrocytes = swell (increase cytoplasm) 4) Calcification zone - Swelling --> mineralisation 5) Ossification zone - Disorganised bone from mineralisation = remodelled