1.7 Bone

Question 1

Primary osteons

Answer 1

• Formed on the outer surface of the cortical bone
• increase the outer diameter of the diaphysis

Question 2

Secondary osteons

Answer 2

• Formed by osteoclasts tunneling through the bone
• Followed by osteoblasts which create new bone to fill in the tunnel
• Produces a new Haversian system that contains a blood vessel

Question 3

what are the components that make
up bone?

Answer 3

Organic: structural proteins provide
strength & flexibility

Mineral: provides rigidity & resistance to
compression

Question 4

Bone matrix composition:

Answer 4

• Type I Collagen
• Other non-collagenous proteins
• Hydroxyapatite mineral —> Ca10(PO4)6(OH)2 Water
• Proteoglycans

Question 5

Woven bone

Answer 5

collagen fibers​ randomly orientated
- first bone formed in fetal development & repair

Question 6

Lamellar bone

Answer 6

mature bone in sheets called lamellae (organized​)

• collagen fibers​ orientated in 1 direction in each layer but in different directions in different layers for strength

Question 7

What is the function of bone?

Answer 7

-Formation of blood cells
-Protection
-articulation (joints/muscles)
-tendon, muscle, joint capsule attachment
-resistance to forces
-vibration transmission
-stores minerals

Question 8

Reabsorb bone, multinucleate cells, least abundent

Answer 8

Osteoclasts

Question 9

Form bone

Answer 9

Osteoblasts

Question 10

Within the bone / master cell

Answer 10

Osteocyte

Question 11

Osteoblasts characteristics

Answer 11

• The “bone-forming” cell
• Extensive ER & Golgi apparatus —> synthesize, modify & export proteins needed for bone formation
• Express high levels of alkaline phosphatase
• Secrete / respond to many growth factors & cytokines
• Active or inactive (flattened) osteoblasts cover most bone surfaces

Question 12

Bone formation by mature osteoblasts

Answer 12

Synthesis & deposition of the organic matrix of bone (osteoid)

• type 1 collagen (90%)
• non-collagenous proteins (NCPs)

Question 13

Mineralisation

Answer 13

calcium + Phosphate = hydroxypatite

Tissue non-specific alkaline phosphatase TNAP -drives mineralization

NPP1 Ecto-nucleotide pyrophosphatase/phosphodiesterase 1 - inhibits

Question 14

Osteoblasts can become incorporated into bone matrix & differentiate into

Answer 14

Osteocytes

Question 15

Which collagen type is most important in bone​?

Answer 15

Type 1

Question 16

What is the most abundant​ cell type in bone?

Answer 16

osteocyte

Question 17

Where is the osteocytes cell body located?

Answer 17

in lacunae

Question 18

Functions of the osteocyte?

Answer 18

• sense load imposed on bone
• trigger remodeling process/apoptosis
• release proteins/cytokines to modulate osteoblast and osteoclast functions

Question 19

Osteoclast

Answer 19

• “bone resorbing “ cell
• formed by fusion of monocyte, macrophage precursors present in marrow/circulation
• large, multinucleate cell
• bind to mineralized matrix –> specialized organ of reabsorption = “ruffled border”

Question 20

bone MODELING definition & characteristics:

Answer 20

-bone formation or resorption with a net change in bone shape
-Evens out stresses, strains
-Occurs at different sites

Question 21

bone REMODELING definition & characteristics:

Answer 21

-bone resorption followed by formation filling in the resorption pit
-Repairs damage
-Occurs at the same location

Question 22

Cell signaling in bone is done by

Answer 22

Osteoclastogenesis which is synthesized by osteoblasts/osteocytes

Question 23

endocrine signaling in bone includes:

Answer 23

-Sex hormones
(estrogen& androgens)
-PTH/ calcitonin: maintain blood Ca2+ homeostasis
-Vitamin D: needed for mineralization
-Thyroid hormone: promotes proliferation/ differentiation
-insulin
-leptin
-growth hormone

Question 24

which ways can bones form

Answer 24

-endochondral ossification
-intramembranous ossification

Question 25

endochondral ossification

Answer 25

-forms most of the skeleton during embryonic development
-Involves a cartilage template which is replaced by bone
-is essential for bone growth & healing

Question 26

intramembranous ossification characteristics

Answer 26

-no cartilage template
-(MSCs) differentiate directly into osteoblasts
(example: in the flat bones of the skull)

Question 27

Fracture healing process:

Answer 27

1) inflammatory
2) reparative
3) remodeling

Question 28

Fracture healing process: inflammatory phase

Answer 28

-hours to days after fracture
-blood from broken vessels forms hematoma around break

Question 29

Fracture healing process: reparative phase

Answer 29

-days to weeks after fracture
-soft cartilage callus forms which is replaced by a boney callus of woven bone

Question 30

Fracture healing process: remodeling phase

Answer 30

-months to years after fracture
-compact bone replaces hard callus through bone remodeling​

Question 31

Endochondral ossification process:

Answer 31

1) MSCs differentiate into chondrocytes and secrete ECM rich in collagen II

2) Chondrocytes undergo proliferation, maturation, hypertrophy & cell death which defines bone shape

3) Primary ossification center forms in the diaphysis of the developing bone

4) Invasion of blood vessels allows infiltration of osteoblasts & osteoclasts

5) Calcified cartilage surrounding hypertrophic chondrocytes is worn away by osteoclasts

6) Bone starts replacing calcified cartilage & spreads longitudinally away from the primary ossification center

7) Secondary ossification centers start forming at the epiphyses

8) Bone replaces cartilage & epiphyseal plate is retained to allow further growth

9) When skeletally mature epiphyseal plates ossify

Question 32

Answer 32

A) Articular Cartilage
B) Trabecular Bone
C) Epiphyseal Plate
D) Marrow Cavity
E) Periosteum
D) Cortical Bone

Question 33

Answer 33

A) Proximal Epiphysis
B) Metaphysis
C) Diaphysis
D) Distal Epiphysis