Bone

Question 1

What are the two types of macroscopic bone and what percentage are they in the skeleton?

Answer 1

Cortical bone (dense outer plate)- 80%
Spongy bone (inner scaffolding-saves weight)- 20%.

Question 2

What does cortical bone contain?

Answer 2

Blood vessels. The cortical bone lining tooth sockets is penetrated by bundles of collagen fibres of PDL (Sharpeys fibres).

Question 3

What is bundle bone also known as?

Answer 3

Alveolar bone.

Question 4

What is the composition of bone by weight?

Answer 4

60% inorganic (hydroxyapatite)
25% organic (collagen, glycoproteins and proteoglycans)
15% water

Question 5

What are examples of proteoglycans and what do they help do to the matrix?

Answer 5

Chondroitin SO4.
Heparan SO4.
They make the jelly texture of the matrix.

Question 6

What are examples of glycoproteins in bone?

Answer 6

osteocalcin, osteonectin, osteopontin and sialoproteins.

Question 7

What does the ground substance of the ECM in bone contain?

Answer 7

It is a semifluid gel which contains long polysaccharide molecules and glycosaminoglycans (hyaluronic acid and proteoglycans).

Question 8

What are the different types of fibres oil the ECM in bone?

Answer 8

Collagen, elastin and other non-collagenous proteins.

Question 9

How can you identify a bone fracture in a histological image of bone?

Answer 9

Woven bone will be present (intertwines).

Question 10

What are the main characteristics of woven bone?

Answer 10

• It is rapidly laid done
• Present in fetus
• Irregular deposition of collagen
• Contains many osteocytes

Question 11

What are the main characteristics of lamellar bone?

Answer 11

• More slowly laid down compared to woven bone
• Contains fewer osteocytes
• Collagen fibres laid down in parallel.

Question 12

How is compact bone organised??

Answer 12

It is laid down in concentric lamellae to form longitudinal columns. They are organised in Haversian systems around a central canal. The candles contain blood vessels.

Question 13

Remember: Volkmanns canals connect/communicate with Haversians canals.

Answer 13

Volkmann’s canals are any of the small channels in the bone that transmit blood vessels from the periosteum into the bone and that communicate with the haversian canals. The perforating canals provide energy and nourishing elements for osteons.

Question 14

What is the other name for a Haversian system?

Answer 14

Osteon.

Question 15

How is spongy bone organised?

Answer 15

It is a network of thin trabeculae (they consist of lamellae). There is osteocytes present and there are no obvious Haversians canals. The bone is thin and nutrients can diffuse through. Bone marrow accompanies the spaces between these trabeculae.

Question 16

Where are osteoblasts derived from?

Answer 16

Mesenchymal cells.

Question 17

What do osteoblasts do?

Answer 17

They synthesise and secrete collagen fibres which forms a matrix.

Question 18

How is the matrix that osteoblasts secrete get mineralised?

Answer 18

By calcium salts.

Question 19

Where are osteoblasts located on/within bone?

Answer 19

They lie on the surface of bone.

Question 20

What do osteocytes do?

Answer 20

They lie within the spaces of mineralised bone and are trapped within. They contact other osteocytes via canniculi. They appear to also communicate with osteoblasts.

Question 21

How do you distinguish between bone and cementum histologically?

Answer 21

Cementum doesn’t contain canniculi. The osteocytes have a radicular arrangement and cementoblasts lie within one side.

Question 22

What do osteoclasts do?

Answer 22

They resorb bone (acid phosphotases) and they lie within concavities in bone (Howships lacunae.

Question 23

What are osteoblasts related to (which cell)?

Answer 23

Macrophages.

Question 24

What are osteoclasts?

Answer 24

Large, multinucleate cells derived from haemopoietic stem cells.

Question 25

How do you spot bone remodelling histologically?

Answer 25

Look for the reversal line. The scalloped edges show where bone resorption changes to bone deposition.

Question 26

What is cartilage?

Answer 26

A semi-rigid, unmineralised connective tissue. The matrix is similar to bone.

Question 27

What is the three different types of cartilage?

Answer 27

1. Hyaline- larynx, nasal septum, trachea, ends of ribs etc.
2. Fibrocartilage- intervertebral discs.
3. Elastic- external ear, epiglottis and eustacian tube.

Question 28

What are specific characteristics of cartilage?

Answer 28

It is formed by chondroblasts and these cells get trapped in the matrix as chondrocytes.
They are avascular.

Question 29

What do chondrocytes contain stores of?

Answer 29

Lipids and glycogen.

Question 30

What are the two types of bone growth?

Answer 30

-Endochondrial ossification=
Long bones. There is a cartilage precursor and the cartilage is replaced with bone.

-Intramembranous ossification=
Flat bones. NO CARTILAGE PRECURSOR AND BONE IS FORMED DE NOVO IN CONNECTIVE TISSUE.

Question 31

What are the two stages of endochondrial ossification?

Answer 31

Initially the cartilage skeleton is laid down and the cartilage is replaced with bone. There are several centres of ossification. Cartilage proliferation occurs at the epiphyses.

Resting zone, proliferative zone, hypertrophic zone and ossifying cartilage.

Question 32

What is a synchondrosis and name an example?

Answer 32

An almost immovable joint between bones bound by a layer of cartilage, as in the spinal vertebrae. Also between the sphinx-occipital bones (cartilage to bone).

Question 33

What is achondroplasia?

Answer 33

A genetic defect of cartilage growth. Endochondral bone growth is impaired. Intramembranous bone growth is unaffected.

Question 34

Note how the alveolar process has been resorbed after tooth loss.
Compare this morphology with the ‘mandibular base’ in the previous slide.

Answer 34

.