MS system - bones

Question 1

Acromegaly

Question 2

Fibro dysplasia ossificans progressiva

Question 3

Functions of the bone

Question 4

Which place in the body has little to know protection?

Question 5

What is bone?

Answer 5

Collagen fibre framework in a mucopolysaccharide-
rich semisolid gel “ground substance”
gives bone its tensile strength
❖ Hardened by precipitation of calcium phosphate
(hydroxyapatite) crystals within matrix
gives bone its compressional strength
(cartilage is similar to bone but
not calcified)
❖ Structural strength near reinforced
concrete but lighter ❖ Made of osteoblasts, osteocytes
& osteoclasts ❖ Supplied by blood vessels & nerves ❖ Contains bone marrow

Question 6

The long bone strucutre

Answer 6

Question 7

Cross section of a long bone

Answer 7

Question 8

What are the two major kinds of bone?

Answer 8

Cancellous and compact

Trabecular and cortical

Question 9

Why is trabecullar bone so important?

Answer 9

It allows for the distribution of stresses eg around femoralk head have high surface area for metabolism ( eg regulation of Ca+2 )

Wihout bone heads would shatter

Question 10

How many times stronger is trabecullar compared to columnar strength?

Question 11

Bloos supply to and from the bone

Answer 11

Question 12

What canals carry blood along the long axis of the bone?

Question 13

What canals carry blood perpendicularly

Question 14

How close are blood vessels to the majority of cells within bone?

Question 15

Which cell is excluded from direct contact from blood vessels?

Question 16

Cortical ( compact ) bone blood supply

Answer 16

Question 17

Blood supply in cancellous ( trabecullar bone )

Answer 17

Question 18

Composition of the bone matrix

Question 19

Common disorders of the bone

Question 20

Osteoblasts

Answer 20

Osteoblast – bone forming cell, cover the surface of bone ….forming an osseous matrix in which it becomes enclosed as an osteocyte

Question 21

Osteoclast

Answer 21

Osteoclast – osteophage; a large, multinucleated cell derived from
haematopoietic cells…In response to mechanical stresses and
physiological demands they resorb bone matrix by demineralization

Question 22

Osteocyte

Answer 22

Osteocyte – bone cell – trapped, “retired” osteoblasts. Mature bone
cells - embedded in lacunae, relatively inactive. Maintain bone
matrix through cell-to-cell communication (via projections in
canaliculi) and influence bone remodelling. Mechanosensing

Embedded within lacunae
Communicate via finger-like projections in canaliculi

Question 23

Osteoprogenitor cells

Question 24

Bone is highly dynamic tissue

Answer 24

equibrillium between osteoblast and osteoclast activity is controlled by signalling between the different cells in bone and via the actions of hormons

• calitonin decreases activity of osteoclasts meaning lower blood Ca levels
• Parathyroif hormone (PTH) increases activity of osteoclasts and releases Ca

Question 25

Trabecular bone remodelling cycle

Answer 25

Question 26

cortical bone remoddeling

Answer 26

osteoclasts reabsorb bone for need

osteoblasts lay down new matrix, eventually get surrounded and become osteocytes

Question 27

Bone mass density is very dynamic and changes all throughout life, what are some of these changes caused by?

Answer 27

Bone mass and density can increase
- Excessive mechanical stimulation
Bone mass and density can decrease
- Non-weight bearing (immobilisation)
- Sex-hormone deficiency (e.g. menopause)
- Endocrine/nutritional disorders
Wolff’s law
- Bone adapts to the load under which it is placed
- Weight-bearing exercise, orthodontic braces, (Amerindian)
head binding

Question 28

Age changes related changes in bone mass

Answer 28

Question 29

what is it called when trabecullar bone is damaged and has breakages between links and webs

Answer 29

osteoporotic

Question 30

Bone growth from fetus to adult

Answer 30

Cartilage model
Formed by chondroblasts
Reshaped by chondrocytes Replaced by bone (ossification)
Endochondral (long bones)
Intramembranous (flat bones) Bone growth begins in the shaft during fetal life

Fetal endochondral ossifcation - ossification begins in the diaphysis and the primary ossifcation centre is active befor ebirth

Question 31

After birth endochondral ossification

Answer 31

Question 32

Bone growth at epiphyseal plate summary

Answer 32

Bone is laid down in the shaft and in the head
The bony parts are separated by a plate of cartilage
As long as the plate of Epiphysis/head
cartilage is present and active the bone will increase in lengt

Question 33

Resting zone - stage 1

Question 34

Growth ( proliferating zone ) stage 2

Question 35

hypertrophic zone stage three

Question 36

Calcification zone stage 4

Answer 36

Calcification zone thin mineral layer of chondrocytes (2-3 layers) where the aging/dying chondrocytes are mineralised by depositing minerals between the columns. This destroys the chondrocytes.

Question 37

Ossification ( osteogenic zone )

Question 38

when does this growth at the epiphyseal plate end ?

Answer 38

puberty

Question 39

fractures in woven bone - in brief

Answer 39

Depends on cells in the local periosteum
Takes 2-4 weeks for healing
– dependent on the severity and position of the
fracture and age of patient
Inflammation and additional blood flow lead to Callus formation
– osteoblasts quickly form woven bone, to bridge
the gap – woven bone is weak as the collagen fibres are
irregular
Lamellar bone laid down
– collagen organised in regular sheets to gives
strength and resilience
Remodelling by osteoclasts to restore original bone shape (more on this next semester…)

Question 40

cartilage

Question 41

Bone

Answer 41

Because the extracellular matrix of bone is inorganic and hard it may seem to be non living. In fact it is a dynamic tissue that undergoes growth, repair and remodelling throughout life
under the influence of a number of factors including the hormones parathormone which
increases the activity of osteoclasts and releases Ca ++ into the blood and calcitonin which
inhibits the activity of osteoclasts and reduces Ca ++ in the blood. Bone matrix (calcium
hydroxyapatite bound to osteoid (mixture of collagen and other proteins)) is synthesised by osteoblasts that become embedded within the matrix but maintain connections with other cells and their blood supply via microscopically small channels. Bone growth occurs when
deposition is greater that bone resorption.
Cells comprising bone tissue lie mainly in the periosteum on the inner and outer surfaces of a bone.
 Osteoprogenitor cells - stem cells that give rise to osetoblasts in bone growth and
repair (compare with “mesenchymal stem cells” below)  Osteoblasts secrete bone matrix (abundant rough ER, Golgi) eventually become
osteocytes  Osteocytes mature cells that maintain bone matrix. Some become buried alive in
spaces in the bone matrix (lacunae) they are connected by cytoplasmic processes
lying in narrow channels (canaliculi)  Osteoclasts are derived from blood monocytes. Large multinucleated cells resorb
bone as they drill through matrix (fracture sites, at epiphyses during growth, and
remodelling sites)  Fibroblasts produce collagen and other fibres.

Question 42

Are bones and cartilage stiffened forms of connective tissue?

Question 43

Long bone structure in a summary

Answer 43

Diaphysis is the shaft of a long bone. It consists of:
● compact bone (osteons or Haversian systems), forms a very strong, light
cylinder that resists compressive (gravitational) forces. Osteocytes are buried
alive in the bone matrix (calcium hydroxyapatite (Ca5 (PO4)OH)). See the
diagram below for a 3D representation of the arrangement of Haversian
systems. ● medullary cavity contains bone marrow supported by cancellous bone. Red
bone marrow is one site of haematopoiesis (formation of red blood cells).
Epiphysis end of a bone that has an articular surface (sometimes referred to as the head). During childhood the ends of a long bone are separated from the diaphysis by plates of hyaline cartilage (the epiphyseal plates) where growth in length of the bone occurs. At the epiphyseal plates columns of cartilage cells undergo division and are eventually removed by osteoclasts. The spaces are invaded by osetoblasts and new bone is laid down. An individualwill continue to grow in height as long as the

epiphyseal plate is active. The production of sex steroids eventually cause the epiphyseal plates to close and the cartilage plate is entirely replaced by bone (synostosis). Girls produce
oestrogen earlier than boys produce sufficient testosterone and so girls cease to grow at an earlier age and are on average shorter than males. In any one individual the epiphyses close at around about the same time (by the end of puberty, largely due to hormonal triggers) – but, in most bones there are multiple secondary sites of ossification, which appear at different ages (before the end of puberty). By observing which of the ossification centres have been formed, it is possible to establish the approximate age of a child.
X-ray imagining can be used to observe these ossification centres. This is possible because bone shows on an x-ray image as black whereas cartilage shows as white.
bone through tendons cause the formation of bone markings such as tubercles and lines)
AH, JI Ed 200918
Periosteum covers all but the articular surfaces and consists of osteoblasts, osteoclasts, fibroblasts. It has a rich nerve and blood supply.

Question 44

Bone is remodelled throughout life

Answer 44

BONE IS REMODELLED THROUGHOUT LIFE Old bone is continuously removed (by osteoclasts) and replaced (by osteoblasts). Normally the processes are delicately balanced to maintain bone mass. Bone is laid down (undergoes hypertrophy) in response to:
 physical stress (training)
 traction and pressure (NB muscular forces through the attachment of muscle to
Trabeculae of cancellous bone are laid down along the line of stress. Bone is lost (undergoes atrophy) in response to:
 lack of weight bearing (immobilisation, astronauts)
 menopause (lack of oestrogen) results in osteoporosis
 dietary imbalance (lack of vitamin D)

Question 45

Bone growth