MS System: Bones

Question 1

Function of bones? (5)

Answer 1

• movement
• protection
• structural support
• storage of minerals
• haematopoiesis - blood cell formation

Question 2

Structure of bone?

Answer 2

• collagen fibre framework - tensile strength
• calcium phosphate (hydroxyapatite) crystals within matrix- compressional strength
• osteoblasts, osteocytes, osteoclasts
• blood vessels and nerves
• bone marrow

Question 3

What is cartilage?

Answer 3

similar to bones but not calcified

Question 4

Parts of a long bone?

Answer 4

> epiphysis - head, articular surface - covered by hyaline cartilage - spongy bone
diaphysis - shaft, hollow cylinder - contains bone marrow in medullary cavity. - nutrient foramen (blood supply) - compact bone
periosteum - fibrous connective tissue sheath covering external surfaces
metaphysics - between epiphysis and diaphysis - region of growth

Question 5

Cells of periosteum?

Answer 5

• fibroblasts - synthesise collagen
• mesenchymal cells - differentiate into osteoblasts and chondroblasts
• osteoclasts - mature bone cells

Question 6

Trabecular/cancellous bone?

Answer 6

• spongy
• porous
• supporting strength to weight bearing end of bone
• trabeculae allow distribution of stresses - have a high surface area for metabolism

Question 7

Cortical bone?

Answer 7

• compact
• forms outside of shaft
• provides stiffness and strength

Question 8

Blood supply to/from bone?

Answer 8

> Haversian canals - blood along axis of bone
Volkman’s canals - blood perpendicularly
- highly vascularised - majority of cells in very close contact to blood vessels (except osteocytes)

Question 9

Structure of cortical (compact) bone?

Answer 9

• cells arranged in concentric circles
• collagen fibres in each layer
• fibres in each layer can be orientated differently - flexible
• osteocytes surround h canal in repeating units
• calcium hydroxyapatite to add strength and harden

Question 10

Structure of spongy (cancellous/trabecular) bone?

Answer 10

• fewer lamellar layer
• less coordinated
• trabeculae create spaces - where haemospoiesis is found - bone marrow

Question 11

Composition of bone matrix?

Answer 11

• collagen - organised parallel arrangement
• crystallised mineral salts - hydroxyaptite
• water

Question 12

Osteoblast?

Answer 12

bone forming cell

• covers surface of bones
• becomes trapped as an osteocyte
• deposit organic matrix (collagen) then hydroxyapatite

Question 13

Osteoclast?

Answer 13

(osteophage)
reabsorbs bone matrix by demineralisation - stress and physiological response
- large
- multinucleated cell
- derived from haematopoeitic cells

Question 14

Osteocyte?

Answer 14

mature bone cell

• formed from trapped osteoblasts
• embedded in lacunae
• relatively inactive
• cell- to - cell communication via projections called canaliculi
• influence bone remodeling

Question 15

Osteoprogenetor cell?

Answer 15

stem cell population - gives arise to osteoblasts (but also other cells)

Question 16

Vitamin D deficiency causes?

Answer 16

rickets - failure of Ca+ absorption

Question 17

Vitamin C deficiency causes?

Answer 17

scurvy - lack of collagen

Question 18

What controls the equilibrium between osteoblast and osteocyte activity?

Answer 18

signalling between bone cells via hormones

• calcitonin - decrease activity of osteoclasts, decreases blood calcium level
• parathyroid hormone (PTH) - increase activity of osteoclasts, releases calcium ions

Question 19

Trabecular bone remodeling cycle?

Answer 19

function - deal with micro damage, scheduled turnover, role in calcium regulation

• quienscence - inactivity
• resorption by osteoclasts
• surface exposed to osteoprogenitors - osteoblasts differentiate
• osteoblasts lay down new bone

Question 20

Cortical bone remodelling?

Answer 20

• cutting cone - osteoclasts reabsorb bone at resorption front
• osteoblasts lay down new matrix - become surrounded and become osteocytes - closing cone
  (more complicated process)

Question 21

Wolff’s law?

Answer 21

bone adapts to the load under which it is placed - weight bearing, orthodontic braces, head binding

Question 22

What increases bone mass and density?

Answer 22

excessive mechanical stimulation

Question 23

What decreases bone mass and density?

Answer 23

• non weight bearing
• sex-hormone deficiency - menopause
• endocrine/nutritional disorders

Question 24

What happens in osteoporotic bone?

Answer 24

spaces between trabeculae increase

Question 25

Bone growth from fetus to adult? during fatal development

Answer 25

bone growth begins in shaft during fatal life
> cartilage model - formed by chondroblasts - reshaped by chondrocytes
> ossification - cartilage replaced by bone - endochondral ossification (long bones), intramembranous (flat bones

Question 26

Fetal endochondral ossification?

Answer 26

• ossification begins in diaphysis - primary ossification site found here
• primary ossification centre is active before birth

Question 27

After birth endochondral ossification?

Answer 27

after birth bone develops at the ends of bone

• at the epiphysis - secondary site of ossification - epiphyseal plate
• at a certain age bone growth stops - cartilage between disappears and bones fuse

Question 28

How does bone growth at the epiphyseal plate work?

Answer 28

• bone layer down in the shaft and head

- bony parts separated by a plate of cartilage - as long as this cartilage is present bone increases in length

Question 29

How do fractures heal?

Answer 29

*remodelling by osteoclasts - dependent on cells in periosteum
nflamation and increased blood flow lead to
- callus formation - osteoblasts form woven bone to bridge gap, this woven bone is weak as collagen fibres are irregular
- lamellar bone laid down - collagen organised in regular sheets to give strength and resilience

Question 30

What factors influence bone healing?

Answer 30

• severity and position of racture

- age of patient

Question 31

Epiphyseal plate zones?

Answer 31

> resting zone - on epiphyseal side of plate - reserve cells
growth zone - cells undergo mitosis - proliferation
maturation zone - cartilage cells transform - enlarging and matrix calcifies
osteogeninc zone - calcified cartilage removed by osteoclasts and replaced by bone secreted by osteoblasts