Bone Development

Question 1

What are the 2 types of bone formation mechanisms?

Answer 1

Intramembranous and endochondral

Question 2

What bones are from the intramembraneous mechanism?

Answer 2

Flat bones of skull and face (mandible, maxilla)

Question 3

What bones are from the endochondral mechanism?

Answer 3

Long bones, spine, ribs

Question 4

Intramembraneous bone formation steps

Answer 4

1. Mesenchymal cells proliferate / aggregate into membrane-like structure, then differentiate into osteoprogenitor cells
2. Osteoprogenitor cells get larger / rounded up, then differentiate into osteoblasts that start producing osteoid
3. Osteoid processes grow via appositional growth on surface. Trabeculae formation into trabeculae networks then into bone tissue

Question 5

Where is the primary ossification center?

Answer 5

Diaphysis

Question 6

Where are the secondary ossification centers?

Answer 6

Epiphysis

Question 7

Epiphyseal growth plate

Answer 7

Cartilage that remains between the primary and secondary ossification centers

Question 8

The diaphysis is located at the ___ of long bone.

Answer 8

Middle

Question 9

The epiphysis is located at the ___ of long bone.

Answer 9

Ends

Question 10

Formation of primary ossification center

Answer 10

1. Nutrition supply blocked, chondrocytes hypertrophy and die and the cartilage matrix calcifies
2. Periosteal buds grow into calcified cartilage, bring osteoclasts and osteoprogenitor cells
3. Osteoclasts remove the calcified cartilage, making the marrow cavity
4. Osteoblasts deposit bone matrix on top of calcified cartilage, forming mixed spicules
5. The mixed spicules (trabeculae) removed later by osteoclasts

Question 11

Why do the chondrocytes hypertrophy and die?

Answer 11

The nutrition supply via diffusion through cartilage matrix (70% water) is blocked by the calcification of the matrix

Question 12

The formation of secondary ossification centers is by similar processes to the formation of the primary ossification center. T/F

Answer 12

True

1. Chondrocyte hypertrophy and death
2. Matrix calcification
3. Blood vessel invasion

Question 13

Bone collar

Answer 13

Compact bone that encases the primary ossification center of the diaphysis, providing structure and support during endochondral bone formation

Question 14

The perichondrium is replaced with the ___ and chondrogenic cells are replaced with ___.

Answer 14

Periosteum, osteoprogenitor cells

Question 15

Mixed spicules

Answer 15

Temporary trabecullae structures of bone matrix (deposited by osteoblasts) on calcified cartilage
Removed later by osteoclasts

Question 16

Where do the chondrocytes begin to die?

Answer 16

Diaphysis, primary ossification center

Question 17

Formation of mixed spicules

Answer 17

1. Osteoclasts and osteoprogenitor cells migrate in via periosteal buds
2. Osteoclasts remove calcified cartilage
3. Osteoblasts form bone (deposit osteoid) on remaining calcified cartilage

Question 18

The mixed spicules are a permanent structure. T/F

Answer 18

False, they are transient and are removed by osteoclasts

Question 19

Long bones, spine, and ribs are formed by ___ while flat bones of skull/face are formed by ___.

Answer 19

Endochondral bone formation

Intramembraneous bone formation

Question 20

Calcified cartilage is stained ___ and is ___, while bone is stained ___ and contains ___.

Answer 20

Basophilic, acellular (chondrocytes have died)

Eosinophilic, osteocytes

Question 21

Metaphysis

Answer 21

Cartilage that separates the medullary cavity and epiphysis

Question 22

The epiphyseal plate continues to grow until ___.

Answer 22

Puberty

Question 23

What are the 5 zones of the epiphyseal plate?

Answer 23

1. Reserve cartilage
2. Chondrocyte proliferation
3. Chondrocyte hypertrophy
4. Calcified cartilage
5. Resorption / deposition

Question 24

The epiphyseal plate growth is bidirectional. T/F

Answer 24

False, it is unidirectional towards the center.

Question 25

The lengthening in endochondral bone growth occurs from ___, while thickening occurs from ___.

Answer 25

Interstitial growth in epiphyseal plate Appositional growth under periosteum

Question 26

How can you differentiate intramembraneous and endochondral bone formation?

Answer 26

Intramembraneous - has same staining color and osteocytes throughout Endochondral - different staining colors and no osteocytes in CC

Question 27

Describe the 5 zones of the epiphyseal plate. What color is bone? Calcified cartilage?

Answer 27

Zone of preservation - chondrocytes at rest Zone of proliferation - chondrocytes start to stack on top of each other Zone of hypertrophy - chondrocytes become larger (glycogen accumulation, vacuolation) and die Zone of calcified cartilage - Cartilage becomes blue/purple Zone of resorption/deposition - blue CC being removed by osteoclasts, bone (red) forming by osteoblasts

Question 28

The epiphyseal growth can be regulated by growth hormone and nutrition. T/F

Answer 28

True

Question 29

What is the function of bone remodeling?

Answer 29

To replace immature bone and maintain/change original shape, replaces aging osteons in mature bones

Question 30

Bone remodeling is random resorption an deposition of bone matrix. T/F

Answer 30

False, it is selective

Question 31

Bone remodeling begins ___ and ends ___.

Answer 31

In utero, at death (throughout life)

Question 32

Bone remodeling units

Answer 32

Cutting zone: resorption by osteoclasts | Closing zone: new bone formation by osteoblasts (mature into osteocytes) or bone lining cells (endosteal cells)

Question 33

In bone remodeling units, the cutting zone contains ___, while the closing zone contains ___ or ___.

Answer 33

Osteoclasts | Osteoblasts, bone-lining cells

Question 34

Primary / woven bone

Answer 34

Formed quickly by osteoblasts, random collagen organization (nonlamellar), more cellular, less mineralized

Question 35

Secondary / lamellar bone

Answer 35

Made from remodeling of woven bone | Parallel collagen sheets (lamellae), less osteocytes (organized in osteons), mineralized

Question 36

Calcitonin

Answer 36

Inhibits osteoclast activity and bone resorption

Question 37

Parathyroid hormone (PTH)

Answer 37

Promotes bone resorption by osteocytes and osteoclasts

Question 38

Estrogen

Answer 38

Activates osteoblasts to produce / secrete bone matrix, inhibits osteoclast activation, decreases with age in women (osteoporosis)

Question 39

Bone fracture and repair

Answer 39

1. Granulation tissue: loose CT around injury site from fibroblast and periosteal cell proliferation 2. Soft callus: dense CT and cartilage for stabilization 3. Bony callus: cartilage calcifies and cancellous bone forms 4. Remodeling: cancellous bone remodeled into compact bone, callus removed

Question 40

The soft callus is made from what?

Answer 40

Dense CT and cartilage

Question 41

The bony callus is made from what?

Answer 41

Calcified cartilage and spongy bone