Bone and Cartilage I

Question 1

Mesenchymal condensations:

Answer 1

• clusters of cells that give rise to cartilage and/or bone in the limb bud of an embryo.
• predict the form and loction of the mature skeleton.

Question 2

What determines the fate of mesenchymal condensations (i.e. whether they differentiate into cartilage or bone):

Answer 2

• proximity to vasculature
  
  • avascular = cartilage
  • vascular = bone

Question 3

Mesenchymal condensations with vascular will form:

Answer 3

bone

Question 4

How does cartilage form?

Answer 4

1. cells of mesenchymal condensations give rise to chondroblasts
2. chondroblasts produce ECM (type II collagen and proteoglycans)
3. chondroblasts completely surrounded by ECM become chondrocytes
4. perchondrium forms outer border of cartilage and produces more chondroblasts

Question 5

Perichondrium:

Answer 5

• Forms outer border of most cartilage
• Generates new chondroblasts around the perimeter of the forming cartilage

Question 6

The two distict layers of perchondrium:

Answer 6

• fibroblastic (gives rise to fibroblasts)
• chondrogenic (gives rise to chondroblasts)

Question 7

Chondrocytes are trapped in:

Answer 7

• ECM
• chondroblasts become chondrocytes when they are completely engulfed by the ECM they produce

Question 8

What type of cell is this?

Answer 8

chondroctye

• lots of rER and golgi to secrete ECM (type II collagen)

Question 9

The two ways cartilage can grow:

Answer 9

• interstitial (from within)
• appositional (from periphery)

Question 10

Cartilage characteristics:

Answer 10

• avascular
• chondrocytes in lacunae
• type II collagen
• matrix is 75% water

Question 11

Nutrition in cartilage is dependent on:

Answer 11

• diffusion through its watery matrix

Question 12

Isogenous groups/cell nests:

Answer 12

• clonal groups of cells due to interstitial gorwth of cartilage
• all derived from a single chondrocyte progenitor

Question 13

The two matrices surrounding chondrocytes:

Answer 13

• territorial:
  
  • immediate border
  • basophilic
• interterritorial:
  
  • outer border
  • acidophilic

Question 14

What are the red circles surrounding?

Answer 14

isogenous groups in cartilage

Question 15

What kind of cartilage is this?

Answer 15

elastic

Question 16

What type of cartilage is this?

Answer 16

fibrocartilage

mix of type 1 and 2 collagen

Question 17

Articular cartilage is a form of hyaline cartilage. What makes it different from the other forms of hyaline cartilage?

Answer 17

no perichondrium

Question 18

Characteristics of fibrocartilage:

Answer 18

• intermixed with dense CT
  
  • type 1 and 2 collagens
• no perichondrium

Question 19

Cartilage matrix composition:

Answer 19

• type 2 collagen
  
  • fibrocartilage has some type 1
• Glycoproteins
• 75% H2O

Question 20

Bone matrix composition:

Answer 20

• type 1 collagen
• mineralized
• <10% H2O

Question 21

Bloody supply in bone versus cartilage:

Answer 21

• bone = VASCULARIZED
• cartilage = AVASCULAR

Question 22

Two ways bone can form:

Answer 22

• endochondral (cartilage scaffold)
• intramembranous (direct; no cartilage scaffold)

Question 23

Steps in intramembranous bone formation:

Answer 23

1. mesenchymal condensations gives rise to osteoblasts
2. osteoblasts produce type 1 collagen matrix
3. osteoblasts become osteocytes
4. Matrix mineralizes

Question 24

Osteoid:

Answer 24

• unmineralized bone matrix surrounding osteocytes
• becomes mineralized quickly

Question 25

Periosteum:

Answer 25

• surrounds osteocytes in the bone matrix
• produces osteoblasts for appositional bone growth

Question 26

Bones can only grow via:

Answer 26

• appositional growth (from the periphery)

Question 27

Label all:

Answer 27

Question 28

Canaliculi:

Answer 28

• Tunnels in bone that connect osteocyte lacunaes that allow for:
  
  • communication between osteocytes
  • nutrients and waste flow

Question 29

Label:

Answer 29

• circle = canaliculi
• arrows = lacunae

Question 30

Can osteocytes divide?

Answer 30

• no
• therefore, bone can only grow via appositional growth (from periphery)