Bone as a tissue

Question 1

Structure of bone

Answer 1

Compact cortical bone
cancellous trabecular bone
Lamellar bone=mature bone that replaces woven bone
Woven bone=immature/unorganized

Question 2

Diaphysis

Answer 2

shaft of bone

Question 3

epiphysis

Answer 3

Ends of the long bones, separated from metaphysis by a physis

Question 4

Metaphysis

Answer 4

region between epiphysis and diaphysis

rich in trabecular bone

Question 5

Cortical Bone porosity

Answer 5

Very dense compact bone
5-30% porosity
diaphysis of long bones and thin shell of bone ends

Question 6

Trabecular bone porosity

Answer 6

cancellous bone
30-90% porosity
axial skelton and ends of long bones

Question 7

Osteons/Haversian System

Answer 7

make up majority of cortical bone in diaphysis
where artery, vein and nerve pass through the bone
osteocytes live within lacunae

Question 8

trabecullar bone

Answer 8

Fine interlacing network surrounded by fat and hematopoietic marrow

Compared to cortical bone:
greater SA and more metabolically active

Question 9

Woven bone

Answer 9

greater cellularity
variable direction of collagen fibrils
immature, randomly and rapidly produced osteoid
predominates in the fetus and pathology (fracture)

Question 10

Lamellar bone

Answer 10

parallel collagen fibrils
mature bone progressively replaces woven bone
1) Cortical: circumferential, concentric, interstitial
2) Trabecullar: trabecular lamellae, parallel to long axis

Question 11

Inorganic component

Answer 11

60-65%
total body mineral stores–Ca, P, Na and Mg
Calcium hydroxypatite (HA) has close aposition with collagen for bone strength and hardness
matrix formation to mineralization takes 12-15days

Question 12

Organic component

Answer 12

35-40%
bone cells and extracellular matrix proteins
predominant cells are osteoblasts,osteocytes, and osteoclasts
ECM proteins=collagen(95%) and ground substance(5%)

Question 13

Factors for generation stimulation of bone formation

Answer 13

insulin-like growth factors

bone morphogenetic proteins

Question 14

Osteoblasts

Answer 14

found on bone surface; derived from mesenchymal cells
Inadequate Ca/P, mineralization lag–>osteoid accumulates
morphology depends on activity: Cuboidal (active) flattened(resting)

Question 15

Osteoblast function

Answer 15

deposit osteoid-type I collagen and ground substance

Initiate mineralization

Question 16

non-invasive assessment of osteoblast activity

Answer 16

measured in the serum:
1-bone specific alkaline phosphatase
2-type I procollagens
2-osteocalcin

Question 17

Osteocytes

Answer 17

Inactive osteoblasts (10%)
trapped in formed bone
mechanosensors
cytoplasmic processes and cannaliculi:
1-transportation and communication
2-continuous mineral regulation

Question 18

osteoclast

Answer 18

multinucleate phagocytic cells responsible for resorption
derived from hematopoetic heirarchy-tissue macrophages and circulating monocytes
can be reconstituted quickly

Question 19

Noninvasive monitor of osteoclast activity

Answer 19

1-tartrate-resistant acid phosphatase (TRAP)=osteoclast specific
2-Type I collagen degradation products (cross-linking telopeptides)

Question 20

Howship’s lacunae

Answer 20

Formed by osteoclasts

Ruffled border of Osteoclast composed of microvilli that appose bone increasing the SA

Question 21

Self-containing extracellular space of Osteoclast

Answer 21

Howship’s lacunae confines destruction to one area:
1-microvilli attach
2-create an isolated enviroment
3-pour hydrogen ions to destroy bone matrix

Question 22

Lysosomal function of osteoclast

Answer 22

1-H+ pumps acidify, solubilizing mineral

2-acid phosphatase and collagenase, cathepsins proteases degrade matrix

Question 23

Collagen

Answer 23

major fibrous component synthesized by connective tissue cells (in bone, osteoblasts)

• -19 types with triple helix hallmark
• -aggregates with ECM proteins for tensile strength and integrity
• -vary in amino acid composition, moleculat size, structure, and ability to form fibrillar to hexagonal aggregates

Question 24

Ground substance

Answer 24

Proteoglycans: flexibility and resilience
Glycosaminoglycans: bound to proteoglycans; cementing substance in lamellar bone between mineralized collagen fibril layer

Question 25

osteocalcin

Answer 25

most abundant noncollagenous organic component

Calcium binding during mineralization, osteoclast recruitment, regulate remodeling

Question 26

osteonectin

Answer 26

avid binding to collagen and mineral

KO: trabecular deficiency, few mature collagen cross-links

Question 27

Bone Sialoprotein

Answer 27

connective, immune, mammary, and neoplastic cells

initiates mineralization and regulates maturation and remodeling

Question 28

Periosteum

Answer 28

two layer:
outer fibrous support
inner osteoprogenitor cells for formation, growth and healing
Greater thickness, vascularity and adherence in immature bone
All long bone except:
1) cartilage, ligament, tendon, or joint capsule
2) femoral neck: subcapsular area–Healing issue??

Question 29

Nutrient artery

Answer 29

enters at a foramen and branches proximal/distal to endosteum

Question 30

Metaphyseal vessels

Answer 30

from periarticular tissue (like epiphyseal)

MAIN supply of metaphyseal trabeculae

Question 31

Periosteal capillaries

Answer 31

from soft tissues that attach to bone

femur–linea aspera

Question 32

mechanical properties of bone

Answer 32

collagen is stronger in tension, hydroxyapatite is stronger in compression
hydroxyapatite is relatively brittle, collagen is more elastic and ductile

Question 33

Function of the skeleton

Answer 33

1-size and shape
2-mechanical support
3-movement-especially the formation of levers
4-protection-skull, pelvis, ribs
5-hematopoiesis and lymphopoiesis
6- mineral reservoir and homeostasis-Ca,P, Mg, Na