Week 1- Bone Formation

Question 1

What kind of collagen is:

• hyaline cartilage
• fibrocartilage
• bone
• growth plate
• lymphoid organ stroma

Answer 1

hylaine (AKA articular)= type 2

fibrocartilage = type 1

bone= type 1

growth plate= hyaline=type 2

lymphoid organ stroma= type 3 = reticular fibres

Question 2

What are Sharpey’s fibers?

Answer 2

Connect periosteum to bone…turn into Volkman’s canals in the bone

Question 3

Does the epiphysis have cortical bone?

Answer 3

No, it is trabecular with hyaline cartilage on top.

Question 4

What are the parts of a long bone? What are they called in an adult vs. a child?

Answer 4

The epiphysis contains the secondary ossification center

The metaphysis contains the growth plate

The diaphysis contains the primary ossification centre

In an adult it is diaphysis and metaphysis

Question 5

What are the periosteum layers?

Answer 5

outer: fibroblasts, nerves, blood
inner: osteoprogenitor cells, osteoblasts..

anchored to bone by sharpey’s fibres.

On outer surface of bone

Question 6

Where is the endosteum

Answer 6

surround trabeculae, in contact with marrow cavity

has osteoprogenitor cells

Question 7

What kind of cell do osteoblasts and clasts come from?

Answer 7

blasts: mesenchymal
clasts: monocyte progenitor

Question 8

What are cement lines?

Answer 8

Cement lines are uncalcified matrix that contains little collagen. They occur on the outer limits of new haversian systems and appear to cement the new system to the remnants of the old

Question 9

What is a physeal scar?

Answer 9

A faint line of xray after the closure of the physis

Question 10

What are the phases of fracture healing?

Answer 10

1. Inflammatory:

Question 11

Describe endochondral ossification

Answer 11

Endochondral Ossification:

1. Make the hyaline cartilage model
   a. Chondrocytes come from mesenchymal cells
   b. Grow in length (chondrocyte division) AKA interstitial
   c. Grow in width AKA appositional (new chondrocytes from perichondrium
2. Make a bony collar
   a. Perichondrium→ periostium
3. Bony collar chokes the chondrocytes and they die. In the middle is a cavity, on the ends are areas of calcified matrix
4. New vessels grow in the space bringing osteoprogenitors from the periosteum
5. Make trabeculae on cartilage spicules- this is the primary ossification centre
6. Secondary ossification centre forms in the ends of bones trapping an area of cartilage between them = growth plate

Question 12

What process turns the soft callous into hard callous (woven bone)?

Answer 12

Endochondral ossification

Question 13

What are the phases of fracture healing?

Answer 13

1. Inflammatory: hemotoma brings cells that clean up the tissue necrosis and start building the soft callus
2. Repair: endochondral ossification turns the soft callus intoa hard callus
3. Remodelling: woven bone is replaced by lamellar or cortical bone

Question 14

What are the zones of the growth plate?

Answer 14

Question 15

When do the limbs start developing in utero?

Answer 15

mesenchyme condenses ~ 5th week

Cartilgae model 6th wk

Question 16

What are the three parts of the somites? What is the apical ectodermal ridge?

Answer 16

Myotome, sclerotome, dermatome

front limbs rotate externally so joint is posterior, hind limbs rotate internally so joint is anterior

apical ectodermal ridge is the part at the end of the limb bud

Question 17

Which bones form via endochondral vs. intramembranous ossification?

Answer 17

endochondral: long bones, vertebrae, weight-bearing
intramembranous: flat bones of skull, clavicle, mandible

Question 18

What enzyme minearalizes bone? what cells does it come from?

Answer 18

alkaline phosphatase from osteoblasts

Question 19

Secondary vs. primary bone healing

Answer 19

Primary is when the fracture ends don’t move relative to each other (the gap is < 1mm…e.g. stress fractures)

Secondary is when the ends do move relative to each other.

Question 20

How does bone modelling happen

Answer 20

• growth in girth (periostal formation)
• growth in length- the growth plate
• matphyseal inwaisting (endosteon is osteoblastic to thicken cortex, perisoteum is osteoclastic to narrow the whole bone)

Question 21

What secretes the alk phos that calcifies the cartilage at the calcified cartilage zone of the growth plate?

Answer 21

the chondrocytes do.

Question 22

How does the bony collar form?

Answer 22

by intramemebranous ossification…